I have noticed that when I assert that no matter how advanced technology becomes, no one will ever make a perpetual motion machine, I get little argument. People accept this as a law of nature, and any technology that obeys the laws of physics is subject to it, no matter how advanced. Technology isn’t magic, after all (Yes, yes. I know the Clarke quote).
I have also noticed, however, that if I say that no matter how advanced technology becomes, no one will ever travel faster than light, I get great resistance from a lot of people. A sufficiently advanced technology could do it, they insist.
Why? It’s not like relativity is an iffy law and not as well established as thermodynamics.
It seems to me that faster than light travel has entered our culture, through sci-fi, as a common trope and people are loth to incorporate its impossibility into their thinking (we want Star Trek, damnit!). Our conceptions of the future are so shaped by imaginative visions that require >c travel, that there is a “mental energy barrier” to giving it up.
Thoughts?
[If no one disagrees, this belongs in MPSIMS, but I suspect someone will want to defend the possibility of “warp drive”]
If you think a perpetual motion machine can exist, I suggest you read over the Laws of Thermodynamics. They (essentially) read as such:
You can’t win
You can’t break even
You can’t get out of the game.
I think part of the reason FTL travel is somewhat more accepted–besides sci-fi influence–is because there are a number of wild-nonsensical theories that might just be right about * getting around it. *
The idea is that you don’t necessarily travel faster than light, you just get there sooner…or something like that. Ehh, I’m sure they’re all wrong anyway
I don’t hold for the laws of thermo dynamics as axioms.
The universe itself could be a perpetual motion machine. Big bang, big crush ad infintum. It depends on who you ask. And just how much mass is in the universe.
Myrr21, great breakdown of the big three!!! now ted,
that’s not perpetual motion. the universe is not goin anywhere, Ted.
and sure it depends on who you ask. you could ask the guy behind the counter at the Sev who needed my help putting a mop together, but all he’d say to you is, “Gguh, could you help me with this mop?”
Oh, don’t get me wrong. I’m not saying I don’t hold it as a law. I’m saying I don’t hold it as an axiom. Just like I don’t hold gravity as an axiom, or any other principle that science uses.
I find it unlikely that Thermo dynamics will every be resinded, or an exception made. But that doesn’t mean I don’t think it’s possible.
Same way people didn’t think anything could go faster than the speed of light in a vacum. Turns out there’s evidence to the contrary, no?
How is that not perpetual motion? If the universe explodes, than colapses, then explodes and colapses, again and again and again forever and it’s not perpetual motion, then what would you call it?
Ted- do you really trust the NY Times for accurate science reporting? Also, the term “perpetual motion machine” is usually used to mean something that continues to move despite leaking energy.
Then you are using “perpetual motion machine” wrong. A PMM has to continue without any outside energy. If it’s leaking energy, then eventually you will have to put more in–in some form or another.
As for the universe, there’s no real way to have much insight into that–especially since that theory is not by any means evidenced or accepted and more than the five other ones out there (ok, two)…
http://www.newscientist.com/news/news_224832.html
As far as perpetual motion machine, goes, I’ve understood it to be one that continues forever w/o having to put extra energy into it. Wheter it leaks energy or not.
Stuygu - Nope sorry. Didn’t intend to do that.
Myrr21 - I know. That’s why I said it depends on who you ask. A lot want to believe that this is what eventualy happens… but many doubt there is enough mass in the universe to create enough of a gravtional pull to bring eventualy bring everything back together again. shrug
Ted, the expansion and posited future contraction of the universe is not motion because motion is defined as movement through space. if space itself is expanding, then it doesn’t count as motion (however, there can be (and is) motion through expanding space). this is why the universe can expand faster than the speed of light, yet not break einstein’s barrier.
oh, and by the way, i get what you were saying about your number one. but do you regard it as a law? i understand not taking a saying for scientific truth, but are you rejecting the saying itself? “stuff falls if you drop it” is not great scientific theory, but that doesn’t mean that the law of gravity is any less valid.
** Jb_farley ** - shurg If you go by that defintion I supose so. Though I admit, I don’t really understand what you’re getting at. I’m merely saying that from my understading of the big bang (all the mass in the universe located in one place suddenly exploding) and the theory of a compact (all the mass in the universe becoming reattracted to itself and reforming into that one isolated space) seems to me to be in perpetual motion. The machine is all that mass, located within the universe (universe being all that empty vacume)
It’s a completly elemetry understanding of the universe, I know. And prehaps I’m missing somthing that I don’t really understand about physics. So I aceed that I could be wrong.
Though I’m not sure what you mean when you talk about the universe going faster than light. I was merely stating that recent experiments seem to show that the speed of light can actualy go faster than what we thought. shrug Like I said, I don’t know too much about physics.
Do I regard it as a law? Hmmm… let’s say that I think of it the same way as I would most things. Could I imagine it possible that we have made a mistake in our perceptions about the law gravity? Sure I could. Do I think we have? Nope.
I’m not saying that scientific laws ARE invalid. I’m saying that they always have the potentail to be invalid… same way Michalson and Morley found out.
** Myrr21 **
A PMM is - “The hypothetical continuous operation of an isolated mechanical device or other closed system without a sustaining energy source.”
It doesn’t have to leak energy and keep going to be a PMM, it only has to keep going with out additonal engery.
Subtle difference, but a difference none the less.
You’re missing my point–it * can’t * leak energy and be a PMM. Anything that leaks energy will–without additional input–eventually stop. Therefore it won’t be a PMM.
So a PMM has to be perfectly efficient, but law #2 of thermodynaics tells us that that can’t happen.
I’m saying the second law of thermo dynamics applied to the big picture, Times Arrow, isn’t nessecarly true.
It doesn’t account for the rest of the laws of the universe, such as gravity.
That the universe will cool off spread out and slowly disapate into a vast wasteland of infinity isn’t a fact, it’s only a possiblity.
Perpetual motion machines have been classified into three types:
Machines which neither consume nor produce energy. E.g. a flywheel in a vaccuum with frictionless magnetic bearings comes close. Or how about a current in a superconducting loop? Such machines can be used to store energy, but don’t do a lot else.
Machines which use the same energy over and over again. This requires entropy to go in reverse, which doesn’t seem to happen very often.
Machines which generate energy from nowhere. This would be a real money spinner! Designs are ingenious and often it’s difficult to figure out why they won’t work. So far, none have.
You could argue that since all the energy/matter in the universe appeared from nowhere in the Big Bang, it is possible to get energy from nowhere. It is theoretically possible to extract zero-point energy from a vaccuum using the Casimir effect, but as to actually DOING it, don’t hold your breath.
As far as the second law of thermodynamics goes, if you accept it blindly it implies that the final state of the universe will be perfect disorder, all energy and matter spread out evenly at the same temperature. This has been called the “heat death” of the universe, because everything will stop. I think Ted is making the point that this won’t happen - gravity would pull such a state back together, for one thing. So the second law has limitations, there are situations where it appears to fail.
Speed of light - I agree with the OP, we have been mentally conditioned by sci-fi to believe it is only a matter of time before we figure out how to break it. There’s also the fact that people don’t really understand WHY nothing can go faster than c; the closest analogy people have is the sound barrier, which is totally inappropriate.
Energy spontaneously tends to flow only from being concentrated in one place
to becoming diffused and spread out.
Given this, all the engergy in the universe is likely to slowly disipate overtime, expanding a finite amount of “stuff” through an infinte amount of space.
However because of other laws, such as gravity, all this “stuff” also has the possiblity of comming back together only to create a new big bang and start to process over. A PPM.
It’s only a theoretical PPM, but it still is a possible PPM given the laws of the universe.
But let’s put that aside for a second. In fact the laws of thermo dynamics DO NOT state that any given system will lose energy, they only state that it is likely to happen. Point of fact is that it doesn’t always happen. You could build a machine, and it could be a PPM, it’s just that over an infinte amount of time that chance becomes the limit of 0.
It’s still a chance, but for all practical matters it ain’t going to happen if the laws of probablity remain true.
okay, let’s look at it like this. the universe is not a system like a motor is a system. whereas a motor must lose some energy due to heat, the universe cannot lose energy. aanother one of those pesky rules of thermodynamics. so it’s rather unfair to say that the expanding/contracting universe would be a perpetual motion machine.
second, in the event that there is eventual recollapse, and the arrow of time does not reverse itself, what are we left with? matter that is being squeezed denser and denser. so heat builds. disorder increases. just like in the real universe.
