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July 3

efficiency of underfloor heating

OK, so I'm still weighing up underfloor heating in our bathroom. But I can't get a handle on its efficiency. What proportion of the heat generated by the wires ends up in the bathroom, and what proportion goes down into the earth and is wasted? underfloor heating didn't answer this. Thanks in advance, Robinh (talk) 05:46, 3 July 2014 (UTC)[reply]

Generally electric heating is quite efficient, but you're correct that some can go down under the house, in this case. Now, what it does once it gets under the house depends on what's down there. If you had a crawlspace, almost all of that heat would escape back to the atmosphere. If there's just earth directly underneath, then that is a good insulator, so the heat will mostly stay put and eventually much of it will work it's way back into the house. However, if there's water draining under the house, that heat can get into the water and drain away that way.

However, keep in mind that electricity is generally an expensive way to heat a home, so that less efficient gas, oil, or wood heating might actually be less expensive. StuRat (talk) 14:10, 3 July 2014 (UTC)[reply]

the floor is on about 150mm of concrete, over a layer of 25mm-sized stones (is this called "hardcore"?), which is directly laid on very clay-ey soil. soil thermal properties is helpful here but I'm having difficulty translating that information into a percentage heat loss figure for my bathroom. What thickness of soil do I use for working out thermal flux? Robinh (talk) 19:49, 3 July 2014 (UTC)[reply]

There are just too many unknowns, like the rate at which water flows through the area. I'd just call it 90% efficient (as a WAG). StuRat (talk) 22:15, 3 July 2014 (UTC)[reply]

In general, current energy code standards would require substantial insulation under a new heated slab. The problem is that unlike a cold storage warehouse, which has similar issues in reverse, the amount of slab heating won't be constant, and if you want to warm the place up you're fighting thermal mass, making it hard to control. It's a common issue in passive solar home design and there are no hard-and-fast guidelines. Much depends on the subsoil equilibrium temperature in your area. Acroterion (talk) 02:18, 4 July 2014 (UTC)[reply]

Time travel and Jaws

If you could go back in time, and you go to Amity Island whilst the attacks depicted in the book (and later film) Jaws were taking place, would it be possible to go on the boat with Brody and Hooper and Quint and go and hunt the shark? And also what would happen if you were eaten by the shark? Horatio Snickers (talk) 18:21, 3 July 2014 (UTC)[reply]

Nothing. It wasn't a real shark.KägeTorä - (^影_虎) (Chin Wag) 18:47, 3 July 2014 (UTC)[reply]

I am not talking about the model shark that appears in the film, I am talking about the actual shark the story is based on. Horatio Snickers (talk) 19:39, 3 July 2014 (UTC)[reply]

The movie is based on a book but changed some from the book. Further breaking it down, the book is a pastiche of several different attacks. Which essentially makes the work fiction. So, your question can't be answered as you seem to be asking it. If you're asking about a paradox in which you die, presumably, earlier in time than when you were born, see time paradox. Dismas|^(talk) 20:27, 3 July 2014 (UTC)[reply]

"If you could go back in time" automatically defines a given story as fiction, so anything is possible after that. And unless your actions prior to your birth somehow affect your having been born, there's no paradox in this scenario. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:37, 3 July 2014 (UTC)[reply]

Quint was an antisquamite. -- Jack of Oz ^{[pleasantries]} 20:36, 3 July 2014 (UTC) [reply]

He didn't like scaly things? Tevildo (talk) 21:47, 3 July 2014 (UTC)[reply]

Time travel back in time to a point where time travel hadn't been invented yet is not possible, especially into a fictional story. Even if it was true, the planet itself from 30 years ago would be in a different part of the galaxy. You'd need some sort of receptor, and because they haven't been built yet, we can't do it. KägeTorä - (^影_虎) (Chin Wag) 00:12, 4 July 2014 (UTC)[reply]

Yes we can. It's fiction. HiLo48 (talk) 00:55, 4 July 2014 (UTC)[reply]

Kage must not have read The Number of the Beast before. Dismas|^(talk) 01:49, 4 July 2014 (UTC)[reply]

：：：：No, only heard the Iron Maiden song of the same name. KägeTorä - (^影_虎) (Chin Wag) 02:55, 4 July 2014 (UTC)[reply]

Fiction is not bound by the laws of physics. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:12, 4 July 2014 (UTC)[reply]

That depends on the type of fiction. While pure fantasy can just invoke "magic" with no explanation given, good sci fi should follow the laws of physics, and the other sciences, or at least some believable extension of those laws. StuRat (talk) 14:16, 4 July 2014 (UTC)[reply]

Depends on the definition of "good". Every time Star Trek goes backward in time, it's inherently bogus. But it makes for an entertaining story. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:32, 4 July 2014 (UTC)[reply]

Yes, like that one they had about "New Age, hey, let's save the whales" hocus-pocus nonsense. The earth has had extinctions for all of the time it has existed, and we are still here. I am not saying we should kill all the whales. I am just saying that it's nonsense. KägeTorä - (^影_虎) (Chin Wag) 17:30, 4 July 2014 (UTC)[reply]

When humans are the agent of extinction, it's a different story. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:47, 4 July 2014 (UTC)[reply]

Are you referring to a particular Star Trek episode, or to the campaign to save the whales? Because if it's the latter, the only thing that caused the whales to be in danger in the first place was mankind... Horatio Snickers (talk) 19:15, 4 July 2014 (UTC)[reply]

I believe Star Trek IV: The Voyage Home is the referent. I've not seen it myself. Tevildo (talk) 20:27, 4 July 2014 (UTC)[reply]

IV is the one about the whales. It's one of the most entertaining in the series. The original series had a backwards-in-time episode. Deep Space Nine had one in which they revisited "The Trouble with Tribbles". The Next Generation had one in which they were caught in a "time loop". A couple of the Next Generation movies had backwards time travel as a major plot device. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:44, 4 July 2014 (UTC)[reply]

This is very interesting. I will be watching the Star Trek episodes you mention! So what is the case you are saying, is it that if I go back in time and am eaten by a shark, I am essentially machine-gunning my grandfather? I am aware they are the same thing - but who would choose to take a holiday on Amity Island in 1975 with the power of forethought? Horatio Snickers (talk) 00:36, 5 July 2014 (UTC)[reply]

What has your grandfather got to do with it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:21, 5 July 2014 (UTC)[reply]

He's referring to the time travel paradox that killing your grandfather before he conceived your parent would prevent you from ever having been born, thus your grandfather was never killed, then you were born, then he was killed, etc. However, if you go back in time and get yourself killed, that won't be a paradox in any obvious way. Although there is the butterfly effect, where even small changes tend to magnify and become global, given enough time. The usual workaround to time paradoxes is to say that you can go back to a time and place identical to your history, but it isn't actually your history, just a parallel universe. So, whatever you mess up there only affects the future there, not in your own time-line. This fits in nicely with the many worlds hypothesis. StuRat (talk) 03:01, 5 July 2014 (UTC)[reply]

I know what he's referring to, but that wasn't part of his premise, so I don't get why he's bringing it up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:19, 5 July 2014 (UTC)[reply]

You don't even know my grandfather. Horatio Snickers (talk) 11:22, 5 July 2014 (UTC)[reply]

You said, "If I go back in time and am eaten by a shark, I am essentially machine-gunning my grandfather." Why? How? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 6 July 2014 (UTC)[reply]

I see. I was indeed referring to the fact that if I go back in time, am consumed by a shark in the year 1975, and therefore would not exist in 2014 any more than if my grandfather never existed. I may have been using a slightly flamboyant turn of phrase, but other users seemed to understand what I meant. Horatio Snickers (talk) 15:02, 7 July 2014 (UTC)[reply]

No, your original life cycle would still stand. Your future self would have been consumed in 1975, but your present self would still have been born in 1980 or whenever, and in let's say 2020 you hop into a time machine, go back to 1975, and become shark bait. There's no paradox. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:10, 7 July 2014 (UTC)[reply]

According to the film Primer, which is fairly solid on physics, one cannot go back in time beyond the moment the time machine was built. So, fictionally speaking, all else is irrelevant. Fylbecatulous talk 14:11, 6 July 2014 (UTC)[reply]

Since there's no such thing as a backwards time machine, that premise is only true within that film. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 6 July 2014 (UTC)[reply]

This question is ultimately about the effects of time travel on pop-culture, not merely whether or not Jaws is based on a true story. Since time-travel doesn't exist yet, the most that can be offered is theories, and had the question been "what do different theories of time travel have to say about affecting the past," it wouldn't have been closed. Instead, the question comes across like humanity has any solid idea of how time travel works yet, which could result in an opinion-based conversation about time travel. Ian.thomson (talk) 15:16, 7 July 2014 (UTC)[reply]