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May 8

is Occam's Razor the only thing propping the Big Bang theory up?

Paleontologists don't presume to be certain of the huge asteroid that presumably ended dinosaur life on Earth. Even though this happened only 65 million years ago, and any evidence for it is still right on Earth. Meanwhile, astrophysicists seem quite sure of what happened 13.8 billion years ago, even though any evidence for it is spread throughout the Universe and there was nothing that "existed" at the time that would have been able to record it or otherwise have a robust record.

So why are physicists so sure, given that "anything" could have happened at that time or before - we cannot possibly have direct evidence of it (unlike the Earth showing a huge place where an asteroid crashed into it.) It seems more like a prediction based on the laws of physics that we use today.

So is the only thing the Big Bang has going for it is that with the laws of physics we use today, and what evidence we have, it would be the "simplest" explanation of the origin of the Universe?

I find the detailed analysis of what happened second-by-second in the first nanoseconds of the universe to be completely speculative otherwise. Our Big Bang article says, "Approximately 10⁻³⁷ seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially" according to big bang -- that's an awful precise number for something that happened "approximately 13.8 billion years ago." You're telling me what happened in under 10⁻³⁷ seconds, even though the event you're talking about happened 13.8 billion years ago?

That seems extremely bizarre for me. The only way I can possibly believe it is if you add, "assuming Occam's Razor", that the simplest explanation is the correct one, this might be justified. So is that the only thing the Big Bang has going for it? 212.96.61.236 (talk) 01:11, 8 May 2014 (UTC)

There are tremendous amounts of empirical evidence in support of the Big Bang Theory, least of all being the nature of the black body radiation distribution of the cosmic microwave background. These details you speak of are not simply hypothesized on a blackboard and stuck with because they are simple. They are formulated based upon observations of the physical universe around us, based on the physical, measurable conditions of that universe. These observations and their data are used in support of the Big Bang theory, and used to refine our understanding of the conditions of the Big Bang. As an aside, your comparison to the dinosaur killing asteroid is somewhat flawed. Not all of the evidence is on Earth. Indeed, most of the evidence for the asteroid doesn't exist on Earth or anywhere else. Processes such as erosion on Earth destroy that evidence. The same processes are not necessarily applicable to cosmology, i.e. a river of water or the action of sea waves can't erode away the microwave cosmic background radiation. --OuroborosCobra (talk) 01:20, 8 May 2014 (UTC)

How can we have "empirical evidence" of what happened in the first 5 seconds of the Universe? Even if we start at the 5-second mark and inflate the Universe from there, it would account for everything we see. Where do scientists get off on tracing the origin of the universe within less than 5 seconds, giving precise descriptions of the nature of the universe at the 10⁻³⁷ second mark? It seems only because they are able to bring the physical rules they've developed elsewhere, to bear. It's not direct evidence of anything that happened in the first five seconds... 212.96.61.236 (talk) 01:54, 8 May 2014 (UTC)

Also, another reason why paleontologist shy away from directly saying "an asteroid killed the dinosaurs" is because the available evidence doesn't really show that, at least not in such simple terms. We do have enough evidence to definitively say that an asteroid hit... but not that it alone killed the dinosaurs. A lot of other changes, such as climatic, were already in progress. It is likely that a mass extinction event of some level was already taking place before the asteroid hit, and that the asteroid just made it that much worse. --OuroborosCobra (talk) 01:26, 8 May 2014 (UTC)

Just about anything you can say in science is subject to Occam's razor. For example, you could say that either Newton's claim that every action has an equal and opposite reaction is true - or you could say that invisible pink dancing hippo's are the cause of such effects. With enough caveats and assumptions, I'm sure we could make an argument that because the hippo's are invisible, intangiable, silent, massless and have unlimited magical powers, we are unable to detect them directly.

So I can *easily* come up with a million possible explanations for any observed set of facts - only Occam's razor says "Why imagine invisible pink dancing hippo's when Newton's laws are so much simpler?" - so we presume Newton is right.

In the case of the Big Bang, the math fits the observations pretty well - and much better than other plausible theories. So while we can't definitively say "God didn't do it" and "Invisible dancing hippo's didn't do it" (or any of a million other possible theories) - we can say that the simplest explanation is that the Big Bang happened the way that science says it did.

Humanity has had HUGE success in using Occam's Razor to eliminate bogus alternative explanations - and the success of "The Scientific Method" is clear to anyone who looks at the technological leaps we've been able to make as a result of that new science.

SteveBaker (talk) 01:44, 8 May 2014 (UTC)

You bring up an excellent point, because Newton's laws are demonstrably empirically false, on a both micro and macro scale. The Universe doesn't actually follow Newtonian motion precisely, at any scale. Likewise, I consider it extremely likely that the Big Bang theory as presently described does not actually match reality as it happened. i.e. that at 10⁻³⁷ seconds into the life of the universe, it didn't look anything like we're saying it did based on the "big bang model". I appreciate that it might be the "best" model we have, but you can't tell me we have any real evidence of the first five minutes of the Universe. Anything could have happened. Further, Physics is not unified (GR and QM are at odds) so we know for a fact that the laws of physics we take to be true, cannot be true. Under this handicap, the idea of making exact statements about the first five seconds of the universe, happenings 13.8 billion years ago, is ridiculously naive. We know for a fact that we are using theories that are false (because we use both QM and GR and they are at odds), under conditions we don't have laws for (both would apply at that scale) and yet we are confident in making a declaration. I find it sophistry. 212.96.61.236 (talk) 01:54, 8 May 2014 (UTC)

Do you make a habit of criticizing whole scientific disciplines from your armchair? —Quondum 02:40, 8 May 2014 (UTC)

As a matter of fact, no - I, too, think the emperor's new clothes look stunning! I was just asking some questions about it. Did you have any more specific thoughts on the matter, Quondum? How do they look to you? 212.96.61.236 (talk) 04:00, 8 May 2014 (UTC)

Also as a side note dinosaurs weren't killed off 65 million years ago, just most groups. I have a particularly noisy bunch that wake me up in the mornings. Dja1979 (talk) 03:42, 8 May 2014 (UTC)

The OP may possibly be looking for an argument rather than for information - I can't say - but I have some sympathy with the POV they expressed. IMO, the Big Bang theory and its description in what seems to be minute detail of what happened in the distant past is far from being "obvious" and far from even being comprehensible to (let's say maybe) 99% of the "educated population". The result is that it does engender a certain level of skepticism.

Is there some way, short of an advanced degree, to educate itself and reduce this skepticism? CBHA (talk) 03:57, 8 May 2014 (UTC)

Returning to the OP's questions (at least an attempt). Science is replete with uses of empirical evidence to prove things that happened in the past. For example, we can observe erosion patterns on Mars that are empirical evidence for their having been flowing liquid upon its surface at some point in the past. In a way, think about it like this: let's say you hear a thunderclap, that you precisely record it in a way that allows you to analyze the spectrum of the sound. That precise analysis of that empirical evidence allows you to prove that lightning occurred in the past. Depending on the data available to you, you may even be able to pin down how long in the past that lightning occurred, even if you did not directly observe said lightning in any way. You can prove its existence in the past because it had a directly measurable impact upon the present that you were able to observe and analyze. Your theory is falsifiable in that your analysis of the audio spectrum and other data could have shown the thunder to actually be a sonic boom from a passing aircraft, or a recording someone played on a speaker, or any number of things that would produce differences in the observations from what is predicted for lightning. Now, to bring this to the Big Bang, what occurred during the Big Bang has directly observable effects on the modern universe. Indeed, what occurred during the very short period of time, seconds or fractions of seconds after the Big Bang, had great impact and effect on how the universe then progressed, and thus how it appears today. A specific second 100 million years ago may not have huge impact on the current state of the universe, but a specific fraction of a second an incredibly short moment of time after the Big Bang could have drastic impact on things like the ratio of photons to baryons, or matter to antimatter in the modern universe. We can directly observe these properties today, and thus can deduce the conditions necessary to produce them, just as you can deduce what was necessary to make a spot of light on a wall even if you cannot see the flashlight. --OuroborosCobra (talk) 04:10, 8 May 2014 (UTC)

This is good. So, what is some of the evidence that the Universe didn't start off as a perfect cubic meter and expand from there? (Other than Occam's Razor.) I do consider Occam's Razor to be a good reason to think that if we can imagine the big bang as described, and have laws to describe it that seem to match our experiments, it would make sense to think of it that way. But that's not exactly direct evidence. I was just wondering if there is more direct evidence that the Universe was a point rather than inflating from a larger starting condition.

I appreciate the arguments for the Big Bang but wondered if there is any more direct evidence for it, other than the inflationary Universe that we perceive. Scientists seem quite sure of the big bang itself. But how do they know - other than Occam's Razor -- that there was an actual "bang", from a single super-dense source, in fractions of a second? (Rather than the same Universe inflating from a cubic meter, for example.) It can be like Noah's Flood...just a story. Is there any direct evidence that, for example, the Universe wasn't only ever a cubic meter at its smallest point, when it started? If something created the point, why not create a cubic meter instead of the point? It seems that the reason we can "extrapolate" and say that it must have been smaller earlier, down to a point source - is that very simply the physical laws seem to make sense to us, they have predictive ability and we can even replicate some of the conditions. But this is far from being direct evidence that this is what happened.... except by Occam's Razor... (Unless I'm missing something.) Our article, for example says: "The Big Bang theory is the prevailing cosmological model for the early development of the universe.[1] The key idea is that the universe is expanding. Consequently, the universe was denser and hotter in the past. In particular, the Big Bang model suggests that at some moment all matter in the universe was contained in a single point, which is considered the beginning of the universe." I get that the Universe is inflating - but extrapolating back that it "must have" been a single point seems like a leap of logic, something that doesn't really have any evidence, does it? Other than the fact that the physical laws we know about seem to work there, and we can recreate some of the conditions...hence...Occam's Razor... That is the crux of my question - whether there is any more direct evidence. 212.96.61.236 (talk) 04:21, 8 May 2014 (UTC)

I'm surprised no one has mentioned it yet, the Large Hadron Collider is directly involved in studying early universe physics. We've moved far from "equations on a blackboard", the ideas and hypotheses are being empirically tested and verified. Vespine (talk) 04:52, 8 May 2014 (UTC)

Further, as mentioned above, ALL we have is the theory with “the best fit”, no scientific theory is accepted 100%. There ‘’could’’ be some amazing unknown factor that is completely misguiding our attempts to understand the universe. Like the goldfish in a bowl analogy, This is a deeply philosophical topic and even most scientists don’t bother delving into it much, it’s a topic for philosophers of science. You might find topics such as Model-dependent realism interesting. It basically argues that we can’t know “Reality” with a capital R, all we can do is create models that mimic reality, in as much as those models match reality, we can say this is how reality works, there can even be several equally valid “overlapping” models, such as perhaps quantum and general relativity. Until the models don’t work and then we know we don’t quite have a complete picture. But until that point, if the models work in every way we can test them, the only model we can replace it with is one that works better. So, WHY don’t we consider that the universe started as a 1m square instead of a point? Well because THAT model doesn’t work as well as the current one. Vespine (talk) 05:49, 8 May 2014 (UTC)

Right, but (as I explained, above) there are an unlimited number of crazy theories that can explain the observations we see out there. Occam's Razor is a good way to prune that down to a sensible number that can be investigated more carefully. The "invisible pink unicorn made the universe" creation theory requires an enormous expansion in the concepts that we'd have to accept without evidence - where the Big Bang hypothesis fits nicely into what we know - with almost no new assumptions. That's why Occam says that we should probably assume that the Big Bang is most likely to be true. However, that doesn't mean that we can say "It's a wrap! We now know how the universe was created!"...certainly not! What we do from that point is to use our new hypothesis of the Big Bang to make predictions that we can test...and we've done exactly that by building the Large Hadron Collider to see if some of those predictions turn out to be correct...and so far, they are. We COULD have put our efforts into trying to make predictions about other observable phenomena resulting from the "invisible pink unicorn" hypothesis - but because there are an infinity of similarly crazy theories - it would be impossible to test them all. Hence, we start with the most promising one - and Occams' Razor has proven to be a valuable (but not infallible) tool for deciding which hypothesis to test next. SteveBaker (talk) 14:28, 8 May 2014 (UTC)

Is it really the "most likely" theory, or the "only one that we know to be possible" based on the laws that we have? If we only have one possible explanation of an event, then no matter what that explanation is, isn't it automatically the most likely one? This seems to be the case with the big bang, since there is no direct evidence. That is quite a different situation than if we had, for example, a picture of it (somehow) as well as a theory. But there's just no evidence of anything from that early on, no picture, as it were, so we just have the theory and since we don't have any other ones that have equal explanatory power we consider it the "most likely." But without any direct evidence, that doesn't make it likely at all.

It is similar to how the ancients explained things they had no way of measuring, only reasoning about (and hence why I called it sophistry). Of course their explanation might have been the most likely one (for them), as it is the only consistent one they knew. But without any direct evidence they had an extremely high chance of being wrong, and ultimately proved to be wrong on nearly every question relating to every science. Moreover, as we have inconsistencies between GR and QM already, we have a particularly high chance of being wrong applying this theory to something we have no direct data of. It is a bit like applying the celestial spheres - without any direct evidence of them - despite knowing about an inconsistency, retrograde planetory motion. Since, despite the inconsistency, it's the best and only theory they had. It just seems that historically speaking additional data goes a very long way to informing theories that match reality, and there seems to be quite a lack of anything that actually proves or directly evinces the big bang, other than the apparent inflation of the Universe since that supposed event.

So while Occam's Razor can help prune down crazy theories that match and predict observation, it does not actually assign a high likelihood to any of these. Only actual positive evidence can... (Unless there is some, of the big bang.) 91.120.14.30 (talk) 16:00, 8 May 2014 (UTC)

Are you the original poster with a new IP address? As I said below, there is compelling and specific evidence in favor of the inflationary big bang. Alternative cosmological models are ruled out by data, not by aesthetic considerations. -- BenRG (talk) 17:29, 8 May 2014 (UTC)

The most important evidence for big bang cosmology is the anisotropy of the cosmic microwave background radiation, first measured by COBE. This plot shows the spectrum of the anisotropy as predicted by ΛCDM (green line) and as measured (colored dots). In ΛCDM this anisotropy comes from quantum fluctuations during the inflationary epoch. The alternatives to big bang cosmology can't even naturally explain the near-perfect CMB blackbody spectrum, much less the tiny angular variations in it. Very recently (this March), the BICEP2 experiment announced the discovery of polarization in the CMB that matches the inflationary prediction if the energy scale of inflation was around the GUT scale. If this result holds up, I think it rules out the ekpyrotic universe, which was the only remaining viable alternative to inflation that I ever heard anyone talk about.

The thing about inflation starting "10⁻³⁷ seconds after the big bang" is bogus and I should probably fix it. There's no evidence regarding how or when the inflationary epoch started because it has the same outcome regardless of how it starts. In particular, there's no evidence that it was preceded by anything resembling a big bang singularity, and the modern perspective is that it probably wasn't. Also, times "after the big bang" are defined relative to the singularity of a traditional big bang model with no inflationary epoch. In this diagram, the "big bang" is the point marked zero where the dotted line intersects the horizontal axis, even though the actual expansion follows the solid line. So if we knew how long the inflation lasted (which we don't), and we took the after-the-big-bang times seriously, the time of the beginning of inflation would be negative. -- BenRG (talk) 07:11, 8 May 2014 (UTC)

I am unconvinced that Occam's razor props up mainstream Big bang theory significantly, when a continuous creation cosmology better meets Occam's heuristic "Do not assume unnecessary complexity" by letting our Universe be homogeneous and isotropic in space and time. Stephen Hawking and followers dispute this Perfect Cosmological Principle by declaring that the discovery of Cosmic microwave background radiation shows a snapshot of the oldest light in our Universe, revealing tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today i.e. proof that something extraordinary did indeed happen and therefore "the final nail in the coffin of the steady-state theory". Occam i.e. William of Ockham (c. 1287 – 1347) cannot tell us who is right but gives us good pause to consider on whom the burden of proof lies heavier. 84.209.89.214 (talk) 18:34, 8 May 2014 (UTC)

The key word is "unnecessary". The steady state theory doesn't explain the physical evidence, so a more complicated explanation is necessary. Making the steady state theory explain the CMB radiation would likely involve a lot of complicated justifications to make it fit, where the big bang theory predicted it as a natural consequence of the model before it was physically measured. Katie R (talk) 18:49, 8 May 2014 (UTC)

I don't understand why people are talking about Occam's razor at all, in this context. As I keep saying, steady state cosmologies are ruled out by the evidence. This wasn't always the case, but it is now. This is how science progresses. -- BenRG (talk) 19:26, 8 May 2014 (UTC)

We're talking about it because that's the question we're trying to answer for our OP...check the title! Steady state cosmologies aren't ENTIRELY ruled out. I'm sure we could invent new (untried, untested and unlikely) reasons why the CMB looks the way it does in a steady-state universe...it would be "one hell of a stretch" - but if you're prepared to come up with new laws of physics, you could explain it away. The reason you (and I) are so quick to dismiss that is because we're unconsciously applying Occam by saying to ourselves: "For steady-state to explain the CMB result requires a crazy set of new physical laws to exist - but if Big Bang is true, then it fits pretty much everything we know." -- which is pure Occam. You prefer the explanation that involves the fewest new laws of physics, the fewest crazy coincidences, the fewest alien conspiracy theories and the fewest assumptions of software errors in the computers that extracted the CMB data from that spacecraft. Take, for example, the Simulation hypothesis (which basically says that the universe and everything in it is a simulation running in the computer of some pan-dimensional hyper being). This is impossible to refute - it explains everything we see - and it requires no Big Bang. In terms of pure logical proof, it's every bit as solid as the Big Bang hypothesis. However, we tend to reject it because we don't need that extra layer of complexity...our buddy Occam again. Hence, my assertion that the OP is correct. Occam's razor isn't just crucial in supporting the Big Bang theory - it's crucial for supporting *any* theory of anything whatever outside the realms of pure mathematics. Of course saying that it's the "only thing" is an exaggeration - evidence of the CMB (and redshift measurements supporting the expanding universe and a bunch of other stuff) are also important. But only the "gut feel" of Occam's Razor can ever be the final arbiter between our finest intellectual explanations of the clockwork universe and the naive concept that "God snapped his fingers and made it using magic", or that we're all just a part of a $10 video-game running in the bedroom of some snot-nosed, bug-eyed, hyper-being. SteveBaker (talk) 14:33, 9 May 2014 (UTC)

A microwave background radiation was predicted as far back as 1946 (Gamow & Dickie). I belatedly found report by Wright of an even earlier measurement of the CMB of 2.3 K in 1941, allegedly not interpreted correctly until 1965. 84.209.89.214 (talk) 15:52, 9 May 2014 (UTC) The Lambda-CDM model that tries to account for the structure of the cosmic microwave background emerged in the late 1990s, long after the CMB was detected (Doroshkevich & Novikov) in 1964 and found to have a spectrum resembling a black body at 3 K (Penzias & Wilson, 1978 Nobel Prize). The heroic story we may hear is that P & W decided to make a conclusive test of Big Bang Cosmology by going to look for an expected CMB but, as history tells, they really encountered CMB first as a mysterious noise in their receiver that only motivated them to check their equipment, removing some pigeons nesting in the antenna and cleaning out the accumulated droppings. 84.209.89.214 (talk) 19:55, 8 May 2014 (UTC)

Everything you say is true, but I don't know what point you're trying to make. I think Penzias & Wilson didn't deserve their Nobel Prize, but the CMB is real and we have much better data now. ΛCDM is indeed just the latest iteration of big bang cosmology. The CMB (though not its exact temperature) was indeed predicted before it was measured. So was the CMB anisotropy. ΛCDM is based on those successful earlier models. Non-big-bang cosmologies and simpler versions of big bang cosmology (without inflation, Λ, and/or dark matter) have been abandoned because they don't fit the data, not because cosmologists didn't like them. Many more complicated models still fit the data. ΛCDM gets the most attention because it has the fewest parameters, which is a good example of Occam's razor in action. Occam's razor only applies to theories that aren't ruled out by experiment. -- BenRG (talk) 21:41, 8 May 2014 (UTC)

My first point was to rebutt Katie R's statement that the BB theory predicted CMB radiation "before it was measured" with relevant dates. Your thought that the ΛCDM model needing "only" six parameters qualifies it as "a good example of Occam's razor" should help you understand why its supporters like to talk about the razor - which is where the OP came in. I live in the country that granted the Nobel Peace Prize in 1978 which had plenty of controversy because it went jointly to the instigator of a military Coup d'état and the Yom Kippur War, and to an alleged plotter to blow up the German chancellor. In contrast the Physics prize for that year was relatively uncontroversial and our article on Nobel Prize controversies only mentions an opinion that cosmologist Ralph Asher Alpher should have shared the prize. It was already shared 3-ways to Penzias, Wilson and Kapitsa (the latter for unrelated low-temperature work in 1937 on superfluid helium) and you don't explain why you object to Penzias & Wilson's inclusion. 84.209.89.214 (talk) 23:22, 8 May 2014 (UTC)

That 1946 prediction was based on a big bang cosmology, right? But the background radiation wasn't measured until the accidental discovery in 1964. I'm not sure how that rebuts anything... Katie R (talk) 14:03, 9 May 2014 (UTC)

Not right. In the 1920s and 1930s almost every major cosmologist preferred an eternal steady state universe, and several complained that the beginning of time concept imported religious thinking into physics. In that era one might easily discuss the average temperature of the universe without conceiving it as a make-or-break test of cosmic history. For three years at minimum Gamow opposed the CMB's validity and conceptualization, according to R. Alpher. The "holy father" Lemaître of expanding universe theory spoke only of cosmic ray remnants in his 'hypothesis of the primeval atom or the "Cosmic Egg". Even the term "this big bang idea" seems to have arisen first only in 1949. See History of the Big Bang theory. Year 1949 also contains a lesson that triumphant acceptance of a Nobel Prize, in this case the Physiology or Medicine Prize for development of the leucotomy, is not proof that one is right. 84.209.89.214 (talk) 17:11, 9 May 2014 (UTC)

There are a few points of confusion here. First, the Big Bang theory does NOT say that the universe was a single point at some point in the past; it just says that the universe was much smaller and hotter at some time in the past. Inflation is NOT a proven phenomenon. At this stage it is just a hypothesis, which is why experiments like BICEP2 are trying to detect signatures from inflation.

Second, even in the inflationary era, the temperature would have been well below the Planck scale where we know that GR and QM break down. There is a time in the past where particles would have had energies near the Planck scale, and we don't know what happened during this Planck era. That's partially why physicists are trying to study physics at high energies, e.g. by building the Large Hadron Collider.

An analogy might help. Suppose a nuclear bomb goes off, and you starting measuring the fireball when it's already 5 km in diameter. By extrapolating backwards using known physics, you can determine that the fireball was smaller and hotter in the past. If you extrapolate backwards enough, you find that the fireball had 0 size at a finite time in the past! But clearly this is nonsense--the simple physics model you're using to understand the fireball breaks down, and to understand what really happened before "t=0", another theory is required--namely nuclear weapons design. But can you understand what happened 1 second after the explosion without knowing much about nuclear weapons design? Of course--there's no shortage of people who devote their careers to studying this! How about 1 millisecond? The fireball was still big enough that simple physics can model it. How about one nanosecond, one trillion of a second, one quadrillionth of a second? At some time your fireball model breaks down. For the real universe, this breakdown happens around the Planck epoch, 10^-43 seconds after the Big Bang. Before that, the universe could have been a point, or a cube, or a rhinoceros; we simply don't know.

In the nuclear bomb example, I assumed that the scientist can only see the fireball after it's already 5 km in diameter. However, astronomers can literally look back in time all the way to the CMB by looking at distant galaxies. This is analogous to somebody recording a movie of the nuclear explosion, starting from 1 millisecond after the blast and continuing to the present moment. The video might not be "empirical" in the sense that you can manipulate the past, but it's certainly good evidence of what happened 1 millisecond or more after the blast. --Bowlhover (talk) 23:20, 8 May 2014 (UTC)

The analogy to a movie is connected to the thought that playing in reverse a movie of the presently expanding universe would show it shrinking until its supposed spherical outer horizon, which nobody can pretend to see beyond today, would come into view. As mentioned there are physicists' careers and big budget research machinery engaged in refining this vision. They assure us both that the outer border of the Universe is detected from left-over radiation, that it will never actually be seen or penetrated, and that its composition is so singular that no comparison is possible to judge its existence, or even whether it exists outside itself. Appeals to Occam's razor are unlikely to dampen the excitement this work generates, most recently by the announcement on 17 March 2014 by the BICEP2 collaboration of the detection of inflationary gravitational waves that support an early cosmic inflation faster than the speed of light. 84.209.89.214 (talk) 00:41, 9 May 2014 (UTC)

Sorry, I have no idea what you're saying. There is no physical "border" to the universe. I have never heard any of the things that physicists are supposedly assuring us about. --Bowlhover (talk) 01:03, 9 May 2014 (UTC)

I think this has been a productive discussion. BenRG has explained that current theory actually can't see when or if an initial point existed, but only the outcome of inflation. Bowlhover points out that in any case we have no idea what happened before a Planck volume was reached. In other words, belief in the Big Bang doesn't require belief in a singularity, I suppose because a singularity is by definition a fuckup in the math. In any case the first second of the universe was definitely not a short time, not by the standards of anyone or anything that could exist during that first second.

I think what attracts the endless idle controversy about the Big Bang is that even scientific shows too often try to equate it with a simplified Christian creation myth or otherwise represent that it has more of a metaphysical meaning than it does. The Big Bang doesn't really mean that the universe's past is finite or its future is bleak and boring. It just tells us that the important scales on which things happen - temperature, distance, and time - continually change. Wnt (talk) 03:32, 9 May 2014 (UTC)

Science, and scientific theories, comprise "a journey, not a destination." Scientists use their theories to try to explain the observable evidence and predict what further evidence could look like. The theory or model that works the best at a given moment is always subject to change or fine-tuning. Occam's Razor works. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:53, 9 May 2014 (UTC)

The question we're being asked isn't whether the Big Bang theory is the best explanation of the available information - I think it's clear that it is by far the best. But our idea of what constitutes "The Best Theory" is conditioned entirely by Occam's razor...and that is what our OP is asking us here. Take any physical theory at all and you can ALWAYS come up with an infinity of other explanations that are possible IF you're prepared to come up with new laws of physics or truly astronomically unlikely coincidences or something of that nature. The way we sort through that infinity of possible explanations and decide to choose the one that we do is by implicitly assuming that "Theory A is true because Theory B presumes that a quadrillion-to-one coincidence happened when we did the experiment" or "Theory A fits with the standard and widely accepted laws of physics where Theory B requires that gravity behaves really strangely at distances beyond what we can currently measure". In each case, we're happy to pick Theory A because Theory B requires "too much of a stretch" - not because Theory B is a complete logical impossibility....and that decision is backed up by Occam's Razor: Always choose the theory that requires the fewest new laws of physics and the smallest assumption of coincidences...until proven otherwise by new data. SteveBaker (talk) 14:50, 9 May 2014 (UTC)

What I'm claiming (and if I am wrong on this please state it) is that the fact that a theory is the best one does not make it nearly as likely as if there is no need for a theory, as it's obvious. For example, if someone who doesn't know anything about Earth and is very distant has somehow gotten their hands on a human population graph and knows for a fact that people spontaneously appear who didn't exist before, but don't really have much if any data on Earth, they might assume that the proximate cause of the marginal increase in population is that people are built in factories as a product of the human society, or their version of the idea that storks bring them (but then where do the storks get them?), or that they spontaneously appear out of air in abiogenesis, or that sometimes one individual becomes two, or, that several different kinds of plants and animals can all turn into humans spontaneously (are these plants/animals then products of abiogenesis? What causes their combination into a human? Why don't humans form directly in the atmosphere?). They don't have any further data. In this case *even if* one of their theories is the correct one (that there are two types of humans and under some conditions a pair consisting of one of each time can go through an operation that causes one of them to gestate a new human), and *even if* Occam's Razor causes them to choose it, it is not nearly as sure as we can be. We don't need theories as how it can be that the human population has been increasing without extra humans being shipped to Earth from outside. Described using just the words I just said, without extra information, the puzzle might have a myriad solutions. There is only one actual way in which people tend to reproduce, and we don't need theories on it. We can see it, and outside this perverse example nobody past the age of a few years old has ever needed to ask the proximate cause of a new human. So, likewise, there is a HUGE difference between a theory being the "best" one (consider for example the best theory a precocious four year-old might come up with, without knowing much about people), and actually having enough data that it's totally irrelevant to even talk about theories of the proximate physical process of a new human. My basic question is where on this continuum is the singularity-type creation story around the Big Bang, especially the first few seconds/minutes? 13:04, 10 May 2014 (UTC) — Preceding unsigned comment added by 212.96.61.236 (talk)

Well, your analogy is somewhat flawed. There is a TON of data on which the Big Bang hypothesis is based - so we're not in that extreme situation where there are any number of PLAUSIBLE theories that fit the data. In your example of the aliens and the population graph, they can certainly come up with a large number of theories - all of which might fit the facts without needing any new laws of physics or extenuating circumstances. Occam's razor would be silent about which one to choose - so they'd be forced to say "We don't know". In the case of Big Bang, we're not in that position. There really aren't any other theories out there that fit the facts without needing extreme coincidences or wild new laws of physics...so Occam points us strongly in the direction of the Big Bang as being the 'best' solution to the puzzle.

You'd be surprised how much information our aliens could get from just a population graph. For example, the number of humans has not asymptoted to a steady state level - so if there were a factory making X humans per day - then we know that humans can't be dying off at X per day. We also don't see a linear increase in the number of humans over time - which is what you'd expect if the factory was making X humans per day and none of them were ever dying off. The human population growth curve is more like an exponential curve - which implies that the production rate of the "factory" increases as the population grows. A good hypothesis to explain this would probably include a guess that the number of factories is increasing as the population grows. This in turn suggests that perhaps humans are building more factories...or perhaps that humans make more humans directly - which would be simpler than hypothesising the existence of factories. So perhaps a careful examination of the data - and application of Occam might maybe get them closer to the truth. But it's very hard to speculate because one thing they're bound to ask is that if humans make other humans, how did the first human appear? If they understand evolution and can see that there are other animals on the planet - maybe they'll instantly guess...but perhaps not. We can't know what the aliens know.

Also, making scientific theories isn't a one-time event. We can use our hypotheses to predict results from experiments. So, for example, we believed that the cosmic background radiation might be patchy if the big bang were true...so we build a spaceship - shoot it up there and snap some pictures. When the pictures agree with our predictions, we know that it's much more likely that we're onto the right track. The results from the Large Hadron Collider are in the same realm...we predicted that if Big Bang were true, then certain results would appear in the Large Hadron Collider...and they did. If Big Bang makes a prediction, we test it and the results are NOT as expected - then Big Bang theory is in trouble and we have to look for something else. So far, that hasn't happened.

So, if your aliens can do experiments in order to get a better handle on what's going on...then they'd know something new. Perhaps they can get population graphs for different parts of the world over time...now they might say "If there is a big factory someplace then we'd expect people to gradually move away from the factory after they were made - so we'd expect a certain population distribution. We wouldn't expect to see the populations on remote islands to ever increase. They get their data - and lo and behold, the populations on remote islands grow with a similar sort of curve to the planet as a whole. This is strong evidence that the "Big Factory" theory is incorrect and backs up the idea of humans reproducing by themselves.

SteveBaker (talk) 16:09, 10 May 2014 (UTC)

Steve the reason for my analogy is that we don't need theories about how humans are created today. The chances that 'adults are wrong' and that, in fact, storks really do bring new children (even to remote islands) or new humans really are created in some different way from gestation by one of the genders, is more than a quadrillion quadrillion quadrillion quadrillion times less likely than basically any probability you can name. It is exactly 0. Our (adults') "understanding" of "where babies come from" can't essentially change, period. We see births. Is the Big Bang in the same category? Would the first 5 minutes of the Universe not being essentially as described in this diagram (from the big bang article) be similar in scope to the discovery by scientists that storks bring new humans to parents? (i.e. less than one in a quadrillion quadrillion quadrillion quadrillion chance of happening)? Or is there room for a new theory of those 5 minutes? 212.96.61.236 (talk) 22:09, 10 May 2014 (UTC)

Please read what I wrote above about the singularity, where I said that the Big Bang theory does not state that a singularity must exist; it simply states that the universe was much smaller, hotter, and denser in the past. There is direct observational evidence of the conditions 300,000 years after the Big Bang, because we can see what the universe looked like at the time--it looked like the cosmic microwave background. There is no direct evidence for what happened seconds to minutes after the Big Bang, but Big Bang nucleosynthesis is theorized to have occurred in the first 0.1-1000 seconds. Scientists can predict how much of each element should have been made in that interval, and it turns out that the universe's composition closely matches the predictions (after accounting for the effects of stars).

What happened before the first tenth of a second is less well-known. Inflation, if it happened, would have left detectable signs on the CMB; this is what BICEP2 recently claimed to have detected. The general idea is that known physics is probably valid 10^-43 seconds or more after the Big Bang, so it's not ridiculous to make predictions about what those conditions were like. These predictions can be tested if they change the CMB in some way. --Bowlhover (talk) 17:23, 10 May 2014 (UTC)

I realize that you are saying that the Big Bang theory does not talk about a singularity necessarily existing. But that is not as far as most explanations of the Big Bang (including our article) go. For example, the lede itself says "After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed". That is some awful precise history for something that happened over 10 billion years ago. Nevertheless, perhaps its as sure a thing as the process by which new humans are formed, which has zero chance of being substantially wrong. (e.g. storks bringing them.) Is that how you understand the strength of the general evidence of the "big bang" events? (If you read our article)? That the chances that it "totally didn't happen that way at all" are about the same as the chances that dinosaurs did not exist (period)? (Which, given the fact that we've had direct fossil evidence of them for hundreds of years, is 0. Is any probability that you can name, a quadrillion quadrillion quadrillion quadrillion times more likely than that the history described in the big bang lede 'totally didn't happen that way'?) 212.96.61.236 (talk) 22:09, 10 May 2014 (UTC)

I don't see why you're so bothered by the precision of the time intervals; it's possible to know that a historical event lasted a certain number of days even if the event as a whole can only be dated to within a few decades.

Anyway, big bang nucleosynthesis, the "first three minutes", happened at an energy scale where physics is well understood, between 10 MeV and 0.1 MeV (compare the LHC p-p design energy of 14,000,000 MeV). Later events such as recombination (the first electrically neutral atoms) happen at even lower energies. So there's really no extrapolation into unknown territory here, and very little uncertainty, I think, in the timeline. No one knows what the physics at much higher energies looks like. I think very early after-the-big-bang times were traditionally based on a simple radiation-dominated expansion model where the scale factor goes like t^1/2. The entire unknown-physics era in this model lasts a fraction of a second, so it doesn't much affect the timing of the events that happen after minutes and years. What really matters is the energy/temperature, not the time. I think that stating it in terms of time is a form of popularization, like astronomers quoting giga-light-year distances to reporters instead of redshifts.

The problem with starting the universe later (long after inflation) is the same as the dinosaur-fossil problem: there's no apparent reason for the anisotropy of the CMB to be even remotely close to consistent with inflation if inflation didn't happen. You have to either put in the apparent fossil record of inflation by hand, or come up with another plausible process to generate it. Might someone come up with a plausible process? Maybe. I don't think anyone has any ideas. Starting the expansion really late, like after big bang nucleosynthesis, seems silly, because you're just wasting your chance to let well established physics do some of your fossil-forming work for you. -- BenRG (talk) 01:22, 11 May 2014 (UTC)

All right. So let's say we know how the Big Bang happened from a singularity. Why? If the Big Bang is within the laws of physics, then could we recreate it using an "early universe" experimental setup (like the Large Hadron Collider)? Why or why not? If the Big Bang has no proximate cause then isn't it a bit silly to presume to know so much about it, except how the hell it could possibly have happened? 212.96.61.236 (talk) 02:48, 11 May 2014 (UTC)

As BenRG, Wnt, and I have been repeatedly saying, we do not know that a singularity once existed, nor do we know what happened during the Planck era. The eras following the Planck era are much better-understood than the Planck era. If our article on the Big Bang implies that a singularity definitely existed, then our article is wrong. The portion of the lede that you quoted:

"After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed"

does not assume a singularity existed. We understand Big Bang nucleosynthesis very well, and the chances that it "totally didn't happen that way at all" are about the same as the chances that dinosaurs did not exist (period). --Bowlhover (talk) 03:43, 11 May 2014 (UTC)

But we have the dinosaur's bones. For the big bang, we don't literally have the bang, we have just cosmic background radiation and an expanding universe - right? As well as our physical theories, which seem to describe our universe very well. 212.96.61.236 (talk) 03:47, 11 May 2014 (UTC)

The Cosmic background radiation is "the fossilized bones" of the Big Bang. It proves that at one time, the universe was very, very small. We can also look at the expansion of the universe (which we can see all around us) and run time backwards to see that the universe must have been much, much smaller in the past. We can look at very distant galaxies (and recall that the further out you look, the further back in time you're seeing) - and those distant galaxies have different properties, showing that the universe has changed quite a bit since the earliest times. These are the "fossils" of the Big Bang - we have them, we can measure them. That's why we can say that the Big Bang is about as certain as the Dinosaurs existing. The details are difficult...especially the first tiny fractions of a second...but that's really no different than the big gaps in our knowledge of the Dinosaurs (How did birds evolve from them? What color were they? Just how quickly did they vanish?). However, nothing is 100% certain - some people claim that the dinosaurs lived at the same time as humans and died out during Noah's flood. Other people claim that God put the dinosaur fossils there to test our faith. These theories are hard to disprove - but Occam's razor says that until we see some pretty solid evidence, these are not worthy of serious scientific study because the 'mainstream' theory of the dinosaurs fits the facts perfectly. It's the same deal with the Big Bang...I'm sure there are plenty of other hypotheses out there - but we don't chase them because Occam says that we don't need to until/unless our present Big Bang hypothesis makes a false prediction or can be shown not to work for some complicated reason. SteveBaker (talk) 04:15, 11 May 2014 (UTC)

Everything we know about the world has been in spite of not knowing how it came to be, so there's nothing new there. The reason "the present-day universe evolved from this earlier state that existed for some unknown reason" is better than "the present-day universe exists for some unknown reason" is that the earlier state is simpler than the present-day state.

I don't think anyone ever took singularities literally as physical objects, but many people thought that whatever was really happening in the region of the theoretical singularity was "small", so the known physics was quite close to the absolute beginning of time. Inflation, which can last for a long time and start in an already old and large universe, shows that that assumption was wrong. So now we're back where we used to be, not knowing how it all began, but at least we've pushed the frontier of ignorance farther away from the present.

We can make chaotic high-energy particle soup in a lab but not an extremely homogeneous and isotropic expanding particle soup like the big bang. We can't trigger inflation in the lab because (if nothing else) the energy scale is too high, about 10¹⁶ GeV if BICEP2 is to be believed. -- BenRG (talk) 04:32, 11 May 2014 (UTC)

natural selection

why does it follow that evolutionary mutations that have made it to today in the form of all the species we see must have some "advantage". why couldn't it be that despite the "disadvantageous" mutation lets say a monitor lizard born w no legs was just able to make due and adapt. there was really no advantage at all?66.87.83.54 (talk) 13:58, 8 May 2014 (UTC)

In the short term, a one-off mutation might very well survive and even reproduce. But to become a viable new species, the descendants of the mutant have to do better (on the average) than the unmutated general population. If it doesn't it'll gradually die out - and if it does, it'll gradually take over. What often happens (and probably what happened with the monitor lizard as it evolved into the snake) is that the environment changes in some way. If we suppose that having no legs is an advantage in rough terrain, then most likely, lizards born without legs popped up occasionally - but because they were slower on flat terrain, they couldn't catch as much food - so they'd have a hard time surviving and their descendents would eventually die out. But if a group of lizards got stranded on an island or in some other place with very rough terrain, then when a legless mutant appeared again, it's offspring would actually do BETTER than the other lizards - and with that increased success, would consume more of the food - gradually starving out the lizards with legs. SteveBaker (talk) 14:06, 8 May 2014 (UTC)

Something else to appreciate is how most animals are always living just on the edge of survival, so that any disadvantage, even a minor one, means they die. Slight injuries, minor sicknesses, or just aging past their prime can all be fatal, so a major disadvantage, like no legs, is almost certain to be fatal. (Humans are an exception, since we can count on others to help us out, but most social species would just consider such a member to be defective, and let it die.) Also, mate selection may mean that even if they do survive, they can't find a mate to pass on their genes, since would-be mates also judge them to be defective. StuRat (talk) 14:25, 8 May 2014 (UTC)

This is an excellent question, and the effort to answer it has been a major topic in the theoretical study of evolution. Our article on genetic drift gives a pretty decent overview of the issue, and our article on the neutral theory of molecular evolution may also be useful. As a capsule summary, nearly every evolutionary theorist agrees that both natural selection and random genetic drift play important roles, but the precise nature of their interaction is controversial. Looie496 (talk) 14:59, 8 May 2014 (UTC)

Limb deformities routinely occur but it is adaptation that drives evolution of species. In evolutionary theory the process through which new species are formed is called Speciation and "success" is seen as the ability of the species to maintain its integrity today. For organisms breeding in the wild, that entails correct recognition of one another as potential mates, their fecundity, and sufficient survival skills in the actual environment to sustain a population. Gaining or losing "advantage" in the sense of prowess in competition does not fully explain the working of evolution where every organism is "making do" (not spelled "due") in its given situation, in which strife with members of one's own species for mates and resources is typically commoner than strife with other species. Judging from observations by various animal breeders that sports (i.e. mutations about which we have articles on their occurrence in botany, particularly ferns, and on the human experience of the unintended teratogenic effect of the medication Thalidomide on embryonic limb development) routinely arise, it is predictable that Monitor lizards with limb deformities are regularly hatched at a low rate. It does not "follow from evolution" that these individuals must fail; they represent on-going Genetic variation and may survive though crippled, and thereby contribute to Genetic drift of their own species. However genetic drift, a random process, almost never leads to a new evolutionary species; the driving mechanism for evolution is heritable Adaptation to a changed environment. It is not axiomatic that a parent species must be extinguished by the daughter species that evolves from it. The evolution of the polar bear from the brown bear is a living example of a Paraspecies that gave rise to another living species. 84.209.89.214 (talk) 16:11, 8 May 2014 (UTC)

• Advantage has only one meaning in biology: reproductive success. This can lead to adaptation to the environment--natural selection and adaptation to attract mates--sexual selection. This has nothing to do with what we find aesthetic (sharks with laser beams) or unaesthetic (limblessness). μηδείς (talk) 17:46, 8 May 2014 (UTC)

Ecological fitting and exaptation also contain some relevant material. Suffice it to say, the benefit of traits is highly context-dependent. Some traits that have strong genetic control also end up different in heterozygous and homozygous individuals So e.g. things like sickle-cell disease have a definite disadvantage, but have persisted because the genes that control it are beneficial in some circumstances. SemanticMantis (talk) 19:07, 8 May 2014 (UTC)

Indeed. My favorite example is the issue of adult lactose intolerance in humans. It turns out that lactose intolerance in adulthood is an evolutionary benefit to mammals - and all mammals except humans have it. It's what ensures that a baby animal is weaned from it's mother's milk in time for the next sibling to be born and get the milk it needs without competition from larger and stronger, older offspring. Since we're mammals, humans adults were always lactose intolerant...right up to the point where we discovered farming - and specifically, keeping sheep, goats or cows as dairy animals. When we started to keep animals, there was an evolutionary advantage for adults who could drink milk without getting sick. In times of short-term famine or crop failure, we could drink milk obtained from our animals rather than slaughtering them for meat - so people who (randomly) happened to have this genetic quirk that allowed them to tolerate drinking milk as adults could survive when others could not. So the genetic "defect" that allows this distinctly non-mammalian thing to happen spread rapidly through our species...and nowadays, most humans are lactose-tolerant into adulthood.

However, at some point, our food supplies became sufficiently reliable that lactose intolerance became a pretty minor problem. WIthout an occasional famine to kill off anyone who was not lactose-tolerant, and with some societies not keeping dairy animals anyway - we ended up as we are now - with an essentially random mix of tolerant and intolerant genetics in our population. There is no evolutionary pressure to eliminate lactose tolerance because we typically wean our babies long before then next baby is born...and there is no significant disadvantage to prevent lactose intolerant people from surviving long enough to have children. So the gene neither dies out nor spreads enough to take over the entire population.

So there is no sense here that lactose intolerance (in adulthood) is either a benefit or a defect. Which set of genes prevails depends entirely on the environment - neither is "better" or "worse" - it's a question of which of them is a better fit for the environment you happen to live in.

Notice also, that nature doesn't care much about it being 'inconvenient' to be lactose intolerant. The gene that makes people intolerant prevents them from enjoying dairy products - but in a modern world, that's very unlikely to result in you dying before you can have kids - or even making it less likely that you'll reproduce! So even though lactose intolerant people might be happier if they could enjoy dairy products - so we would say that lactose intolerance is a "genetic defect" - it's unlikely to ever be eliminated from our gene pool. Of course if somehow our culture changed and we gained a rock-solid tradition of only ever making love after sharing a pint of real dairy ice cream (it had better have chocolate chips!)...then the lactose intolerance gene might well be finally eliminated in just a few generations. If the few weird people who insist on breast-feeding their older children until they are 6 years old (yes it happens!) somehow became the societal norm - then lactose intolerance would probably spread rapidly through our population. But unless either of those things happen, we're going to continue to have both kinds of genetics in our makeup.

SteveBaker (talk) 14:08, 9 May 2014 (UTC)

Erm, I think you've gone astray with that just-so story about weaning. It assumes that the offspring is more deterred by eventual diarrhea that it reasons must have been caused by the only food source it's ever known, than by a snarling rebuff from the mother. I would suggest a just-so story about conserving a small amount of energy by not producing a protein when it isn't needed, but that too ought to be taken with suspicion. Wnt (talk) 16:58, 9 May 2014 (UTC)

Wikipedia has information about Lactose tolerance#Evolutionary advantages and history that is correctly punctuated by responsible editors not omitting reliable sources. The mutated gene involved has been identified as MCM6. In unvaried form this gene will, as a person gets older, reduce production in the small intestine of lactase, an enzyme that catalyzes hydrolysis of lactose into glucose and galactose, and the reduction leads to Lactose intolerance. 84.209.89.214 (talk) 22:18, 9 May 2014 (UTC)

Also see [1]. But I have to say, I find something odd about this data, in that it seems to support a simple single-gene model for varying levels of production, with a person being either lactose tolerant or intolerant. Yet in my case, I feel like I start to get diarrhea after eating cheese or dairy products if I go more than about two weeks without eating them first; so to me the lactase seems inducible. My father told me he had something of a similar feeling. But that's not in these sources. Wnt (talk) 22:55, 9 May 2014 (UTC)

Just as a quick remark to Wnt that has not much to do with the OP's question: There are more possible trigger to diarrhea than lactose intolerance. If you only have problems if you didn't eat certain food recently, that would probably more point to a difference in symbiotic bacteria, which are readily inducible. OR: I myself have some food (onions, for example) that I can eat without problems when I'm used to them, but just leaving them out for a few weeks gives problems when I suddenly start eating them again (although reduced quantity and mixing them with other food certainly helps). --TheMaster17 (talk) 09:41, 12 May 2014 (UTC)

Light sensitive element

I had the idea of doing my science project this year about a light sensitive element. I read up on a few, for example Selenium which is used in scanners. I want to do the experiment with an element which alters the flow of electricity through the element (or another inorganic light sensitive compound) when exposed to light.

Now with the theory after me, I need to find such material for the experiment. Does anyone has advice where can I buy or get hold of such material? I've been searching the net but came of with little success. Thanks Romeo Kilo 15:43, 8 May 2014 (UTC) — Preceding unsigned comment added by Proudly RSA (talk • contribs)

Photoconductivity is an interesting phenomenon. Seems like it would be easy to find various photoresistors, or photodiodes and related semiconductors, from an electronics shop or similar hobby/do-it-yourself project source. Selenium itself is probably harder to get (and fairly toxic), and you would have to wire it up youself rather than using prebuilt components as a starting point. There are all sorts of types of photodetectors that operate by various electrical phenomena. DMacks (talk) 15:54, 8 May 2014 (UTC)

Before light metering was built into cameras, a separate Light meter was a common tool for every serious photographer. Far more Weston Standard meters which incorporate a selenium sensor and moving-coil meter were sold than have use today so you may find an old one cheaply. Another type of photodetector is the CdS photocell which is a Photoresistor made from Cadmium sulfide whose conductivity increases when irradiated with light. Unlike a selenium cell, using the CdS photocell needs an external voltage source. This application note explains how it may be connected to an ADC input of a computer. 84.209.89.214 (talk) 17:42, 8 May 2014 (UTC)

Just thinking out loud: suppose you have a material like the silver chloride in a "photogray lens". Somehow, in the light this turns dark over time as the silver comes out, yet reliably regenerates to a clear shade in lower light. I don't really know how that's done, or if there are other materials like it. Now, suppose you had a thick piece of this backed by a mirror out in the sunlight. At first it is clear, then over a few minutes ? it becomes dark because of the sun. Then the transmitted and mirrored light becomes much less, so it ought to clear again, shouldn't it? I wonder if you could end up with an oscillating chemical reaction this way.

Now suppose you had a photoresistor under the photogray material - I'd suppose you could get an oscillating electrical potential out of it? And if you had some material that darkens under exposure to current (like the magic windows on a Boeing 777 that are designed to make sure the inmates can't look out of the plane except when the captain allows it) then you could put that above the photoresistor to get a similar oscillating effect? I wonder if you could make all these components out of a thin translucent paper soaked with the right salts and glued together to make a little "chip" out of paper, and end up making a logic circuit out of it. :) Put together a little like [2] though I picture a very low tech and low resolution version :) Wnt (talk) 17:59, 8 May 2014 (UTC)

Formation of silver chloride from its elements is exothermic and it darkens when illuminated in proportion to the incident light energy. The darkening is due to precipitated silver. Becoming more like a Black body radiator just absorbs more of the light energy, presumably arriving at an equilibrium when recombination energy cancels absorbed energy. What evidence have you that an optical/chemical oscillation occurs? Did you make up the term "photogrey lens"? 84.209.89.214 (talk) 19:09, 8 May 2014 (UTC)

Wnt's mirror idea is interesting if I understand it correctly. There's a slab of glass/plastic/etc with silver chloride, with a mirror behind to reflect light that passes through the slab back to the slab. So first, the slab is transparent, so light passes through, bounces off the mirror, and back to the slab (and back out). The slab is philosophically getting irradiated "two ways" (direct on the front and reflected-transmission from behind). The slab darkens, so now less light is transmitted through to the mirror, so less irradiation from the back. Less irradiation (only the direct on the front), so it becomes clearer. That allows increased transmittance and therefore increased irradiation from the back, therefore darkens. Which reduces the back-side irradiation, so it becomes clearer, repeat repeat repeat.

Couple of possible logical flaws...darkening is a range, not a boolean state, so as it darkens, it gradually reduces the back-reflection, so at some point it would be "just dark enough" to attenuate the transmission "just enough" to hold at that amount of darkening. Equilibrium, but it might take a while to reach? But isn't the light that's not transmitted absorbed by the slab not reflected, and therefore even when darkened contributes to keeping it dark? The blocked light still reacts with the silver chloride, albeit from the front/middle of the slab instead of from the rear, rather than just disappearing? DMacks (talk) 22:14, 8 May 2014 (UTC)

I didn't make up "photogray lens" - it's a specific product, a kind of eyeglasses that darken in the sun. Not a particularly appealing idea for their intended purpose, but what's interesting is that the transition takes (I think) several minutes, which introduces the time delay to the system. My assumption is that the time delay ought to lead to an overshoot and oscillatory behavior, though it is true that by itself, without some other system as I started speculating about, I think the oscillation ought to dampen down pretty quickly. I suppose I was assuming that the light absorbed by silver grains didn't cause further deposition, which may indeed be wrong. Wnt (talk) 16:50, 9 May 2014 (UTC)

What you refer to are clearly Photochromic lens that have been mass produced for outdoor sunglasses since the 60s with no noticeable oscillations. 84.209.89.214 (talk) 18:23, 9 May 2014 (UTC)

There is an incredible range of light-sensitive elements to choose from. For example, you can use a regular LED as a light sensor. If you carefully cut the top off of a DRAM chip, you can use it as a primitive camera because all of those tiny memory cells are light sensitive. There are light-sensitive resistors (photoresistor), light sensitive capacitors, light sensitive diodes (photodiode), light sensitive transistors (see: Photodiode#Other_modes_of_operation)...in fact just about every kind of circuit element comes in a photo-sensitive version. (although I couldn't find a light-sensitive inductor.) SteveBaker (talk) 13:27, 9 May 2014 (UTC)

Here's a page with DIY experiments, one of them a semiconductor light sensor made from copper oxide: http://thesciencecupboard.com/page3.htm Ssscienccce (talk) 15:30, 9 May 2014 (UTC)

Selenium is available at any supermarket as an antioxidant on the shelf with other vitamins. The question of how to extract it from the tablet/pill in pure form is another matter. --AboutFace 22 (talk) 16:44, 9 May 2014 (UTC)

You're talking about a trace, micrograms not milligrams (just ask the Venezuelan polo team...). If you faithfully isolated all the selenium in the bottle you might get enough to register on an analytical balance. Wnt (talk) 16:54, 9 May 2014 (UTC)

An anti-dandruff shampoo with 2.5% selenium sulfide seems a better option... Ssscienccce (talk) 00:37, 10 May 2014 (UTC)

A laser printer or photocopier could well have a selenium coated drum for picking up the toner using electrostatic force. Another possibility is a selenium rectifier, which could have been used in the time before semiconductors. Graeme Bartlett (talk) 21:43, 10 May 2014 (UTC)

Well, if we're going to be practically oriented... how reliable are suppliers on Alibaba.com? (the company in the news over its US IPO recently) I mean, there are merchants on the list at [3] who sound like they would sell you ten kilos of the stuff for $500. (Try not to run through it all at the first bake sale) Wnt (talk) 21:51, 10 May 2014 (UTC)

CDC

What is CDC, in the medical sense? I am trying to add links to Regulatory regulation, and CDC links to a disambiguation page without any obvious medical pages. Jwoodward48wiki (talk) 16:50, 8 May 2014 (UTC)

Centers for Disease Control and Prevention, which is the first link on the CDC disambiguation page. Red Act (talk) 16:57, 8 May 2014 (UTC)

I think the OP means Regulatory translation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:17, 8 May 2014 (UTC)

I don't see any references to CDC in that page. Sounds like OP is looking for CMC, which is "Chemistry, Manufacturing, and Controls." Drug development contains a tiny bit of information on that. Here is the pertinent language: "In addition, drug development is required to establish the physicochemical properties of the NCE: its chemical makeup, stability, solubility. The process by which the chemical is made will be optimized so that from being made at the bench on a milligram scale by a medicinal chemist, it can be manufactured on the kilogram and then on the ton scale. It will be further examined for its suitability to be made into capsules, tablets, aerosol, intramuscular injectable, subcutaneous injectable, or intravenous formulations. Together these processes are known in preclinical development as Chemistry, Manufacturing and Control (CMC)." Justin15w (talk) 20:16, 8 May 2014 (UTC)

SCID gene therapy, retrovirus, leukaemia

Some time ago, an attempt was made to treat SCID-X1 infants with a gene delivered by a retrovirus and some of those children presented with leukaemia a few years afterwards. Did all of those infants (with leukaemia) die as a result? Also, was the risk of cancer not obvious at the time? --129.215.47.59 (talk) 18:06, 8 May 2014 (UTC)

According to [4], 4 of 9 developed leukemia and of those, 1 died. It mentions that parents were informed of a risk of leukemia, though it's not clear whether this is discussing the first gene therapy study or a later one. Mr.Z-man 22:19, 8 May 2014 (UTC)