Wikipedia:Reference desk/Archives/Science/2015 November 8

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November 8

Any good scientists to convince my dad of evolution?

This is following my earlier post asking for evidence of evolution to convince my dad of it.

I did my best, but my only expertise in science is pretty average grades in GCSE's (high school) so it was difficult to respond to certain objections.

Would somebody knowledgable on the subject, especially fossil records, dating methods, etc be available to correspond with him via email? Time and timing isn't a factor, so you would just respond whenever you have a couple of minutes. Thanks, 2.102.187.59 (talk) 02:48, 8 November 2015 (UTC)

It's probably best to get your answers from the Talk.Origins page (see previous thread - this is the URL); or, of course, we can answer them here. One point I would make - you're unlikely to be successful if the argument turns into an attack on his religious faith. You'll need to show him that acceptance of evolution is compatible with Christianity, not that the two are contradictory. A discussion of the spherical Earth theory can be helpful - does he believe that the Earth is round? If so, he's rejecting a literal interpretation of those parts of the Biblical text that say it's flat (Job 26:10, Revelation 7:1), and that the sky is held up on pillars (Psalm 75:3, 1 Samuel 2:8, Job 9:6): will it challenge his faith to reject a literal interpretation of Genesis 1? If he _is_ a Flat Earther, then giving up is probably the best idea. Tevildo (talk) 03:16, 8 November 2015 (UTC)

Talk.Origins just isn't feasible, given just how specific and unrelated to his objections the entries are. In response to this video - https://www.youtube.com/watch?v=54e5Bz7m3do - he grabbed on to the part where the guy said carbon-14 age is changed through solar and geological activity. I think it would be too much back and forth to post here though. Only direct email would work. He's not a flat Earther, just a guy in his 40s with a relaxed belief in Christianity who thinks humans have been here for a few thousand years and it's ridiculous to think we could've been monkeys. 2.102.187.59 (talk) 03:40, 8 November 2015 (UTC)

Well the real point that should be conveyed is that carbon dating is only one of many, many pieces of evidence for evolution and the age of the Earth. Even if someone discovered tomorrow that all carbon dating was wrong, you would still have to explain all the other evidence of evolution. You might want to look at evidence of common descent, age of the Earth, and RationalWiki's list of evidence against a young creation. And maybe "How come there are still monkeys?". The "humans have been here for a few thousand years" is its own special brand of wrong. I'm getting young Earth creationist vibes, unfortunately. Anyway we have evidence of human existence for tens of thousands of years. Maybe ask where he thinks Göbekli Tepe or the prehistoric technology we find lying around everywhere came from. --71.119.131.184 (talk) 08:18, 8 November 2015 (UTC)

Why do you feel the need to convince him of a scientific theory? How would it improve his life on earth? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:19, 8 November 2015 (UTC)

May as well try, no harm in it. 2.102.187.59 (talk) 03:40, 8 November 2015 (UTC)

If he gets mad at you and never wants to speak to you again, would that feel harmful? ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:45, 8 November 2015 (UTC)

I'll just let Carl Sagan answer this question. --71.119.131.184 (talk) 08:18, 8 November 2015 (UTC)

I'll give it a shot - I've convinced a few people in the past. You can find my email address on my user page (User:SteveBaker). SteveBaker (talk) 05:02, 8 November 2015 (UTC)

I think it is important to distinguish between science and religion here - the goal is not to "defeat" religion, but to acknowledge and respect it. An omnipotent Creator could have written up the universe in any order, on any schedule - like a human author, God could write a basic scene with a few plot elements, then stitch in a backstory. Like any author, God might decide to introduce new concepts, change the settings where events happened, alter the very physics of the world being written about, revising the entire draft, beginning to end, as many times as desired. Sometimes an author might even try writing a character into a tough situation to see how he or she would react to it, gain some insight from that, but scrap that part of the draft later (the problem of evil, you might say).

The key then, here, is to recognize that what we are trying to prove is not that the world is random and humans are a haphazard, unplanned thing whose ethics should be patterned on the notion of relentless, mindless competition to pass on genes. We don't know why reality is what it is, or if it sought what it is supposed to accomplish - we can't even prove that what is is; that's an axiomatic faith, not science. No, what we are trying to prove is a much smaller thing, namely, that the world as we observe it (natural science) follows predictable natural laws that we can use to our advantage, and natural selection is one of them.

It is not wicked to read a lesson that God engraved into the world with such precision - the deep time frame implied from telescopic observations of the distance of dim stars and laboratory measurements of the speed of light, or the procession of fossils and their correspondence to the molecular divergence of the genomes of organisms. To the contrary, there is real good to be accomplished by understanding evolution - understanding the evolution of viruses like HIV within the body, the origin of new species like measles, the use of natural selection principles to select a population of cells that display immunological tolerance, and the subsequent clonal selection response against an invader.

Do humans have to follow natural selection as if it were a moral law? No. Natural laws challenge us, and if they cannot be broken, we don't have to worry about breaking them. Darwinism credits Herbert Spencer for inventing the phrase "survival of the fittest", but this doesn't mean that we should embrace a cruel morality, any more than we should jump off a cliff to respect the primacy of gravity. It is at this point that religion shines, showing us other paths to follow that aren't so downward. Wnt (talk) 12:49, 8 November 2015 (UTC)

• To me the most compelling argument is to focus on the age of the Universe. If we look through telescopes, we can see stars that appear to be hundreds of thousands of light years away, and galaxies that appear to be millions or even billions of light years away. How is that possible, if the Universe is only a few thousand years old? Did God create the light we receive in mid-flight, thereby showing us events that never actually happened? Or is the Universe really millions of times smaller than it appears to be? Neither alternative is easy to defend. In Creationist cosmology this is known as the starlight problem. Looie496 (talk) 17:57, 8 November 2015 (UTC)
  • They could say your measurements are inaccurate. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:24, 8 November 2015 (UTC)
    • That's like saying Columbian druglords did it, Bugs. It's an arbitrary objection based upon no evidence (who has better distance estimates?) raised against a position which does have a whole coherent system of observations behind it. If you actually understand the hard sciences, you get to the point where you have to posit an evil demon (brain in a vat) objection, and claim that God is so malevolent he would even order Abraham to murder his first-born son as a . . . I mean is so malevolent he would create fossils and starlight to deceive us. Personally, with a "God" like that, I'd prefer the more reliable company of Lucifer. μηδείς (talk) 22:37, 8 November 2015 (UTC)
      • The point being that a true believer will have a counter-theory for everything the OP poses. I would still like to know why the OP is so hell-bent on creating trouble with his father. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:44, 8 November 2015 (UTC)
        • Yes, even the uber-combative and ever-vindictive Ayn Rand argues that one should not try beyond polite discussion of your own ideas to convert one's parents. As for scientists, I too would go with Carl Sagan. μηδείς (talk) 00:42, 9 November 2015 (UTC)

I have a keen interest in evolution and I have several close relatives who reject evolution on religious grounds. I have listened to literally hundreds of hours of “evolution” debates and have even participated in a few informal debates myself. Let me tell you something from experience: it is nearly impossible to convince someone who doesn’t believe in evolution for religious reasons that evolution is true using facts about evolution. I heard it explained this way which I think is completely true: For religious people their position is like supporting the right football team, it’s not about which position has better “facts”, it’s almost exclusively about being on the “right side”. For them, their “authorities” tell them that to be a good Christian or Muslim or whatever the religion is, they must reject evolution, that’s it, that’s what you are arguing against. Try to convince someone they support the wrong football team, that’s essentially what you are up against. It’s not completely impossible, but it takes a lot more than “facts”. Don’t forget that Satan is the deceiver, the prince of lies, He can make up extremely convincing arguments that support evolution, but it’s not up to your fallible mind to decide for yourself, you need to trust in God to tell you the real truth. That’s the way these people think, that's what you are up against. As for the religious people in my life, I also have not tried to convince or convert them, I agree with the above, it's not worth it. The most I do is occasionally, when there is a cool science story, not even related to evolution, I try to share and discuss it with them to expose them to how real science works and how wonderful it is. Vespine (talk) 23:02, 8 November 2015 (UTC)

I'll ask my original question because I think it's pertinent. Why do you believe in evolution? If your understanding is so limited that you believe it because someone else told you it was true, that is no different and no more authoritative than a creationist viewpoint. You would be better served to learn the science yourself so you can use it as a foil rather than simply relying on an appeal to authority. Believing Carl Sagan more than a creationist simply because he's Carl Sagan is not a rational argument that will convince anyone. --DHeyward (talk) 03:33, 9 November 2015 (UTC)

I actually think this completely misses the heart of the issue. Everyone believes they have GOOD REASONS to believe ALL of their beliefs, including people who deny evolution. NO ONE who has made their mind up on a subject thinks their understanding is "limited". Ultimately, I can't tell you I completely understand radiometric dating, or DNA analysis, or cladistics and I bet you can't say that either: ultimately you have to submit to the expertise of someone who you trust, it just happens that the people YOU and I trust are scientists who have spent their lives learning about this stuff, and people who deny evolution submit to the 'expertise' of people like Ken Ham and Kent Hovind. Of course you can say "but I "understand" how it works, I "see" the evidence of it in action, etc, well i'm afraid the other side say the same thing. Vespine (talk) 04:09, 9 November 2015 (UTC)

And in case you doubt they say the same thing, Kent Hovind has about 10 hours of lectures 'debunking' evolution freely available on the internet. To someone like you and I it's an exercise in logical fallacies, circular reasoning and pseudoscience, but to someone who is on the other side. That's why websites like talk origins and creation wiki can exist side by side for 10 years. Vespine (talk) 04:36, 9 November 2015 (UTC)

To say "I believe in evolution" is an intellectual trap. It turns it into religion. It makes more sense to say "I believe in the scientific method, and the preponderance of evidence we've found so far supports the theory of evolution." ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:00, 9 November 2015 (UTC)

I disagree Bugs. I guess it depends who you are speaking to but philosophically speaking, knowledge is a subset of belief. i.e. The set of all the things you consider to be true are all beliefs, regardless whether you have good reasons and regardless whether they are in fact true or not. The definition of "belief" to mean "take on faith without any evidence" doesn't really exist. No one actually thinks they "believe" anything without good evidence, the difference is what people consider to be "good evidence", not whether they actually have it or not. Vespine (talk) 21:48, 9 November 2015 (UTC)

You can prove the basic concepts of evolution even in the flavors of Doritos. The fittest survive and pass their genes. It's your Dad who need to convince you why God wouldn't use what he already created at it full potential to pursue his creation ? It would be ignorance or madness, but God is an omniscient, perfect and wise. So no ignorance nor any act in vain. Iluvalar (talk) 19:46, 11 November 2015 (UTC)

What is the relation between "coronal plane" to the crown?

How crown can represent this direction of the plan? I don't understand it78.111.186.167 (talk) 06:09, 8 November 2015 (UTC)

Crown is the top (as of a head), or the top surface (as of a tooth). A coronal plane lies between the front and the back. A coronal plane is generally perpendicular to the crown of the thing the crown is the crown of, and intersects it from side-to-side. The Transhumanist 09:27, 8 November 2015 (UTC)

The orientation of the coronal plane is based upon the coronal suture, the junction between the frontal bone and the right and left parietal bones of the skull.[1] BiologicalMe (talk) 17:35, 11 November 2015 (UTC)

Wild horse and horseshoes

How did wild horses survive in the wild without horseshoes? What happens when they experience excessive wear on their hoofs? Or do they not experience excessive wear due to them travelling less or travel on softer ground compared to the domesticated horses? 731Butai (talk) 13:21, 8 November 2015 (UTC)

See Horse hoof and Natural hoof care, suggesting that this isn't really an issue for wild horses. Mikenorton (talk) 14:17, 8 November 2015 (UTC)

It is explained pretty well in Horseshoe#Reasons for use of horseshoes. Traveling more on harder ground is good for a horse's feet, as it toughens them up. It's traveling less, and on softer ground that brought about the need for horseshoes. In answer to your concern about excessive wear, keep in mind that "The average hoof grows 1/4 to 3/8 inch per month. Since the average hoof is 3 to 4 inches in length, the horse grows a new hoof every year." The Transhumanist 18:40, 8 November 2015 (UTC)

I saw a horse living wild in Vieques Puerto Rico which had a hoof that had grown so long that the horse hobbled like a woman on high platform shoes she was not used to. The hooves were several inches longer than normal and curved a bit like an overly long fingernail. Apparently it was not anyone's job to catch the horses and trim their hooves. It appeared to be a mare with a foal. Edison (talk) 22:57, 8 November 2015 (UTC)

• Recently: Neglected Horses Had 3-Foot-Long Hooves,Rescuers Say. μηδείς (talk) 00:37, 9 November 2015 (UTC)

Are distal and proximal in anatomy are used for appendicular system only?

According to what I understand, the distal and proximal terms in anatomy are used for appendicular system only? 14:31, 8 November 2015 (UTC) — Preceding unsigned comment added by 78.111.186.167 (talk)

Those terms are widely used in anatomy: "proximal" means "next to" and "distal" means "not next to". If you enter "proximal" or "distal" into the Wikipedia search box, you will see a long list of possible anatomically related completions. Looie496 (talk) 14:40, 8 November 2015 (UTC)

So you say that the answer is: NOT? and these terms are used also for the axial system? I would like to see an example, because I didn't see.78.111.186.167 (talk) 16:02, 8 November 2015 (UTC)

Er, the wording is a bit confusing, but Looie is saying that the terms are used widely in other areas of anatomy. So, the answer to your question "Are distal and proximal in anatomy are used for appendicular system only?" is no, because these words are used on other systems as well. If you want a concrete example, doing as Looie suggested, I entered "proximal" in to the search box and looked for an entry that did not have anything to do with the appendicular skeleton. The first one I saw was Proximal_convoluted_tubule. These are just English words. We even use related words abstractly for things that aren't anatomical at all, e.g. Proximate and ultimate causation. SemanticMantis (talk) 16:29, 8 November 2015 (UTC)

It looks like the question was poorly worded, and that the question the OP meant to ask was, Are there any bones of the axial skeleton whose names involve the terms "proximal" or "distal"? The answer to that question is that I don't know of any, but I don't know the skeleton all that well. Looie496 (talk)

I meant to ask if these terms are used (in anatomy) except of the area of the appendicular skeleton. (according to what I know it can be used in dermatology or other medical professions but always they refer to the area of the appendicular skeleton rather than the axial skeleton) 18:05, 8 November 2015 (UTC)

The terms are also used in dentistry. Arbalest Mike (talk) 16:24, 8 November 2015 (UTC)

• The very simple answer is no. The tip of the appendix, as an apt example, would be considired distal compared to the proximal end where it joins the intestine. Obviously we're not talking limbs here. μηδείς (talk) 22:26, 8 November 2015 (UTC)

See the figure in Phalanx bone. Proximal and distal are pretty widely used in anatomy - wherever you can describe things as near and far. Wnt (talk) 01:33, 9 November 2015 (UTC)

Granted, though in many cases it makes more sense to use 'medial/lateral' when you're not discussing part of an appendage. 64.235.97.146 (talk) 15:10, 9 November 2015 (UTC)

Can the circadian rhythm adjust to days longer than or shorter than 24 hours?

Since all human beings live on planet earth, they all live on a planet with 24 hours a day, and the circadian rhythm is probably adapted to that. But what happens if a spaceship carries some humans from one planet to another, and on this latter planet, the day is much shorter than earth's, as its rotation is much faster? Will humans be adapted to the new planet? 71.79.234.132 (talk) 15:43, 8 November 2015 (UTC)

Circadian rhythms are also affected by photoperiod, and other Zeitgebers. So even with a 24 hour period, different things happen at different times based on day length, temperature, and other factors. Free-running_sleep gives some references on humans being successfully entrained to a 23.5-hour day and to a 24.65-hour day. See also siesta, polyphasic sleep, and second sleep - even with 24 hour days, many people have broken them up differently. SemanticMantis (talk) 16:21, 8 November 2015 (UTC)

Generally there are a range of durations that people can entrain to. The exact edges of that range aren't precisely defined, because stronger zeitgebers allow a wider range. Studies have shown that people can entrain pretty easily to day lengths of 23.5 and 24.65 hours (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1934931/). (Note that 24.65 hours is the length of a day on Mars.) The maximal range is likely to be substantially wider than that, but hasn't been pinned down experimentally (for humans). Based on animal studies, shortened days will probably cause failure of entrainment more easily than lengthened days. Looie496 (talk) 17:02, 8 November 2015 (UTC)

This article, Non-24-hour sleep–wake disorder, could do with a bit more referencing, but it matches both what I remember having read, and what I know from experience. Most people have an endogenous rhythm slightly longer than a day. On my own I would love a 25-hour day. Way back when I was in college mon-thurs and not working I pretty much followed a 25-hr day or even longer, and ended up staying up all night every few weeks to get back on a semi-regular schedule. Even with the end of daylight savings time, I want to go to bed later than the clock hour, rather than earlier, as one would expect. μηδείς (talk) 00:23, 9 November 2015 (UTC)

The US Navy submarine fleet works on 18 hour days. 6 hours on watch, 12 hours off. The off hours include sleep and training. So I would alternative hours are doable. --DHeyward (talk) 09:51, 10 November 2015 (UTC)

Which flower is this  ?

http://i.imgur.com/8N9Bt00.jpg which flower is this ? — Preceding unsigned comment added by 39.42.44.108 (talk) 18:41, 8 November 2015 (UTC)

Bluebell. --TammyMoet (talk) 20:44, 8 November 2015 (UTC)

which specie? — Preceding unsigned comment added by 39.42.44.108 (talk) 21:00, 8 November 2015 (UTC)

I apologize for being a pedant, but this is an error I see more and more these days, and it bugs me. Specie is not the singular of Species. They are completely different things. Species is singular and plural. Specie means coins. Iapetus (talk) 15:30, 9 November 2015 (UTC)

It certainly looks like it could be some species of Hyacinthoides but what we call a bluebell here in the states is a bit different. Seeing the leaves and knowing the location would help. μηδείς (talk) 22:22, 8 November 2015 (UTC)

The flowers of the common bluebell and Spanish bluebell are quite similar, except that the Spanish version is bigger and has an erect stem rather like the OPs photo. The common bluebell flowers are on a rather droopy stem. The Spanish bluebell is widely grown in British gardens and in some places is threatening to displace or interbreed with our native common ones. See Spanish bluebells threaten future of UK's favourite plant (May 2015) and How can I tell whether bluebells are native ones or Spanish ones?. Alansplodge (talk) 23:03, 8 November 2015 (UTC)

The OP geolocates to Lahore, so if it's a garden plant in that area, Spanish bluebell would seem to be a good bet. Alansplodge (talk) 23:06, 8 November 2015 (UTC)

Normal force in car

Say a car is travelling at a constant velocity, and a person (or, if we want to make things simpler, a block) sits on the passenger seat, with its back and bottom touching the seat. Normally when we sit in a car at constant velocity, we would think that we are in contact with the back of the seat. Yet, if the car and thus the person/block is in constant velocity, then the sum of the forces is zero, so is the normal force exerted by the seat on the person also equal to zero? I ask because, if it was nonzero, what other force could be acting on him? Thank you! 70.54.112.243 (talk) 20:32, 8 November 2015 (UTC)

The seat back angles backward even in its most upright position, so gravity pulls your upper body toward it (obliquely). If the seat back were vertical or tilted forward then you would not press against it unless the car was accelerating or some nongravitational force was pushing you backward. -- BenRG (talk) 21:01, 8 November 2015 (UTC)

With a vertical seat back, you could press against the seat back either by exerting yourself or by scooting your butt forward and slouching in the seat. In both cases the force opposing the normal force of the seat back on the passenger is the friction force of the seat on the passenger's bottom, without which the passenger would slide forward. -- ToE 22:09, 8 November 2015 (UTC)

Put it this way, if the acceleration of the car was truly zero (in a real moving car this would very rarely be the case), then the forces acting on someone sitting in a moving car would be the same as those acting on someone sitting in a stationary car. Vespine (talk) 22:44, 8 November 2015 (UTC)

You could have a seat back which is at a 90 degree angle to the center line of the car and have the car at a constant speed, but the OP did not specify that the car was n a level surface, so climbing a hill could also force the passenger or load against the seatback. As Vespine said, this would be the same as if the car were stationary on the hill. Edison (talk) 22:52, 8 November 2015 (UTC)

• Let's back up. Touching, and being pressed against are two different things. It requires no force for a block touching the back of the seat behind it to remain touching the [back of] seat. Second, if there is no net acceleration, there is no relevant force other than gravity [affecting a human passenger at a constant velocity]--although this still does not have anything to do with a rigid block on a seat touching or not touching the back of the seat. Third, the human body is held only held rigidly upright against gravity by the force exerted by muscles that keep the spine erect. If one relaxes them, one will normally slump back against the seat due to the curvature of the spine; that curvature converts compression of the spine by gravity into a slumping forward of the head and a pushing backwards of the lower back. Fourth? Well, I am not sure there is really a relevant fourth. μηδείς (talk) 00:34, 9 November 2015 (UTC)

In a non-accelerating car, the only force acting on occupants is gravity. --DHeyward (talk) 03:21, 9 November 2015 (UTC)

Meaning that the occupants will accelerate downward at 1 g? -- ToE 06:48, 9 November 2015 (UTC)

No, it means they will only feel the force of gravity. --DHeyward (talk) 08:57, 9 November 2015 (UTC)

It sounds as if the questioner is considering the free body diagram of a nonaccelerating passenger, and rightly expects the vector sum of forces to be zero. The force of gravity on the passenger is countered by the normal force that the seat applies to their bottom, (though just how that force feels will depending on how comfortable the seat is). -- ToE 14:40, 9 November 2015 (UTC)

I understood your comment and its meaning. The normal force exerted by the chair is a function of gravity if there is no acceleration. It's not a property of the chair. The same chair on the moon exerts a normal force that has nothing to do with the chair and everything to do with the mass of the person and gravity. The force that is felt is gravity acting on the person. In space, far away from any massive body, there is still no acceleration but the lack of gravity would change the entire experience of the chair and what is felt. The equivalence that comes into play is when comparing a non-accelerating frame of reference in a gravitational field with an accelerating frame of reference in a non-gravitational field (i.e. the 1g accelerating elevator in space is indistinguishable from the surface of the earth). A 10 kilogram child can sit in a chair and then a 100kg person can sit right beside them in an identical chair. The normal force would always be expressed as a function of mass and gravity and that is why it is the only force felt. The "Free body diagram" helps solve for acceleration and it's convenient to express the chair as exerting a force, but keep in mind that force can do no work. Any work done would be by gravity and I think that's one of the fundamental requirements of force. It's been a while though, so there are probably better examples. --DHeyward (talk) 16:09, 9 November 2015 (UTC)

Radiation resistance

If I send a high frenqency sine wave down a piece of 50 ohm coax that is open at the far end, will there be any detectable em radiation in the space beyond the end of the coax? If not, why not?31.55.80.65 (talk) 21:53, 8 November 2015 (UTC)

See impedance matching and VSWR. _Theoretically_, a perfect open circuit (infinite impedance) will reflect all the RF energy back down the cable (and into the transmitter, which may not like it) - the reflection coefficient will be 1.00 and the VSWR will be infinite. However, a real cable with the end cut off will not have infinite impedance, and will therefore radiate some detectable energy. The actual amount of energy radiated will depend on the impedance match between the cable end and free space, which will be very dependent on the frequency of the RF and the precise geometry of the cut end. Tevildo (talk) 22:22, 8 November 2015 (UTC)

The match is well defined: its 50R looking into 377R. So do we actually detect that amount of power transferred or is it affected by some other factor such as near field effects?31.55.77.23 (talk) 00:11, 9 November 2015 (UTC)

377Ω is the impedance of free space - that doesn't mean it's exactly the impedance that is encountered at the end of an unterminated wire, but it's a pretty decent rule of thumb. If we use free space for the impedance at the end of the unterminated wire, you can use the simplified reflection coefficient equation:

$\Gamma ={Z_{L}-Z_{S} \over Z_{L}+Z_{S}}$

...and note that transmitted power is given by $1-\Gamma ^{2}$. That equation estimates about 40% of the power will radiate away - which is sort of what we expect, because an unterminated 50 ohm trace is a lot like a crummy dipole antenna!

...but because you said you're modeling unterminated coaxial cable - it's more probable that the unterminated impedance is not well-modeled by 377Ω, because of the unique geometry of coaxial cable. Some sources say ∞ is a better model for the unterminated impedance of coaxial cable - if I really cared about the value, I'd use a TDR or a VNA to actually measure my cable in my lab, because this kind of real-world RF stuff defies theoretical calculation!

This is covered in our articles on transmission coefficient, reflection coefficient, and so on. These are simplified equations, and they assume a specific simplified model of the unterminated wire; and it also assumes that 377Ω is a good model for the impedance of the air at the frequency you're using. Nimur (talk) 02:36, 9 November 2015 (UTC)

Working out the radiation resistance of an antenna is far more complicated than the reflection coefficient calculation. The unterminated coax will be a very poor radiator, because almost all the energy that comes out the end goes back in again. The electric field, being radial cancels itself out at a distance, and the magnetic field in the outside cancels that of the inside. If you want more radiation, you can strip back the shield for a quarter wavelength to get a monopole antenna. Graeme Bartlett (talk) 20:27, 9 November 2015 (UTC)

The exposed radiator can be modeled as an impedance so creating a 1/4 wave monopole is effectively reducing the radiative resistance. I think the mistake above is assuming that the maximum radiative resistance is related to the free space impedance. They aren't related that way and the radiative resistance can indeed be "infinite" (i.e. much larger than 377 ohms) just as a short can be "0". The radiative resistance of the quarter wave monopole reduces it from "infinite" to about 38 ohms. I believe the mismatch between the power amp, transmission line and monopole would give an accurate value for reflected and radiated power. --DHeyward (talk) 03:41, 10 November 2015 (UTC)

So does the reflection formula apply or not to the situation of a coax 50r cable(without any baring of the central conductor)? If the theory is different , what is the other theory predicting how much power is radiated into space..?86.187.161.176 (talk) 17:24, 10 November 2015 (UTC)

I believe it's frequency dependent. Visualize a 1/4 wave monopole at 1GHz and calculate the impedance and radiation. Now reduce the frequency to 500Mhz and the percentage of radiated energy changes. Neither the free space nor transmission line impedance changed but the radiation impedance did. It's complex and frequency and geometry dependent. Cell phone antennas have relatively straight forward transmission lines but the antenna shape is a fractal design to maximize radiation in the bands of interest. Directionally focused antenna such as a Yagi-uda antenna are also very tuned to frequency for radiation and reception with many passive elements. They all use very wideband, constant impedance transmission lines so a simple description of the impedance mismatch of the transmission line to free-space is insufficient to describe radiation. The antenna itself (or whatever structure the open wire has) has an impedance that is not independent of geometry or frequency or surrounding passive elements. --DHeyward (talk) 08:53, 11 November 2015 (UTC)