Okay, what do you mean firstly by: everybody move in the speed of light?

Relativity doesn't allow you to add velocities in the sense that 0.75c + 0.75c = 1.5c, but it'll end up to be less than the speed of light, c instead.

And how does this occur?

Corrections:

kmarc

You appear to be shorter in length if you move at some constant velocity relative to an observer


Moving close to the speed of light relative to some observer is not theoretically impossible. FTL currently is theoretically impossible

azarimy:

Not really; to make this clear, we label the twin brothers [1] and [2], [1] being the 'stationary' observer, and [2] being the person on the rocket flying off at some velocity

To [1], time goes by slower for [2]. But here's the important point, if [2] looked at [1], he would also see that time goes by slower for [1]. It's purely symmetrical because they're moving at the same velocity (well, excepting the +/-) relative to each other.

This post has been edited by bgeh: Dec 21 2009, 10:34 PM

That's general relativity, and something that I'm not qualified to discuss, but it seems that they're discussing a method to 'increase the speed of light' in some region of space by introducing a new metric (a perfectly fine thing to do)

Yes, but that's irrelevant. You still appear squashed if you move at a constant speed relative to an observer in special relativity.

Here, let's introduce stranger metrics in General Relativity: Godel metric
http://en.wikipedia.org/wiki/G%C3%B6del_metric

Travelling backwards in time using this metric isn't a problem at all; in fact time is probably an ill defined concept using this metric. The important point is to realise whether this metric is suitable to describe our Universe, and while I don't know enough about GR, I'd suspect the same applies to the link you posted.

Sure, except that to any observer, if you're truly moving at the speed of light, your length will be exactly zero. Your original statement was:


But you do look squashed to any person observing you, even when you travel at a constant speed, this time, being the speed of light.

Future theories might not make it true either; in fact it might end up being an impossibility

Else it'll bring up the question: Why haven't we seen anyone from the future yet?

Note: In the initial statement, I said that FTL is a theoretical impossibility. I said this in the context of special relativity, where an inspection of the equation for the momentum of a particle in special relativity would give contradictions if you allowed a particle with mass to travel at the speed of light, i.e. it is impossible to take an object with mass, travelling at less than the speed of light relative to an observer, and then accelerating it to the speed of light, and hence you can't expect such an object to ever travel faster than light, since it can never pass the speed of light in the first place. There was no General Relativity brought into the discussion at all.

Note 2: I did more reading; the metric introduced by Alcubierre doesn't allow for FTL travel either, or travelling at the speed of light for particles with mass.

This post has been edited by bgeh: Dec 22 2009, 04:36 AM

As to your question, I'm not able to provide an answer - haven't done GR yet [it depends whether the axioms of SR do generalise naturally into GR - from this first look at this metric, it doesn't seem to]

It is also possible that I am your mother/father/grandfather. Have you considered that possibility yet? Or that everything that happens in the universe is actually due to fairies. Or that angels move objects in such a mathematical manner as to be able to be described by our current theories, and they might choose to change it anytime to 'suit' any other theory available.

What I'm trying to get at you is that, sure, anything's possible, but most 'possibilities', when tested, are shown not to occur. It was once thought that atoms were knots in the ether, but that was shown to be wrong. Let your imagination flourish, but I'd advise you not to think that possibility means inevitability, which is what you seem to be implying here. Not all science fiction will turn out to be true.

Or to use your example: Everyone thought the Earth was flat, and then they found it was a sphere. Well, why couldn't it be hyperbolic? Why couldn't it be a Klein bottle? Why couldn't it be a torus? Why couldn't it be various other shapes? - they're all possibilities. Sure, speculate all you want by assuming it's some possibility x, but it is not inevitable that your assumption is correct. But yes, if you indeed want to discuss time travel, and have to assume one of that, go ahead, but always be aware that it depends heavily on the assumption, which may turn out to be false after all

Now, what theory do you propose then, that has physical basis in our universe? (note: GR describes a set of universes, that certain solutions exist with interesting properties, e.g. wormholes, doesn't imply they exist in our universe) That's the big thing distinguishing science from science fiction, which seems to just take a problem, and proposes a miracle solution, and builds something upon it. Fair enough if they want to make stories out of it. But these miraculous solutions may turn out to be completely untrue, which is a more general point I'm trying to make here, and which is why I've been posting in this bloody thread so much

Yes, in a sense I'm saying they're irrelevant, because the existence of such a theory hasn't been shown yet, and even if it exists, FTL (we're making the assumption here that FTL means time travel - this might not be true either) might never be possible in all these theories, which is the point I'm trying to get at here really, and there are reasons for that, for one, causality, and wrecks the idea of entropy, mass-energy conservation, etc, etc... (again, assuming FTL does mean time travel, backwards). Sure these concepts might end up being replaced in the end, but the strength of a new scientific theory is that it is able to explain all previous phenomena explained by the scientific theory it succeeds, and be able to describe something new that the previous theory wasn't able to, i.e. it would still have to explain how those concepts I put up above still 'work' within its new framework.

This post has been edited by bgeh: Dec 22 2009, 10:05 AM

I used the word imply. There was no explicit mention of it, hence the word imply. You're implying that future theories will allow such a thing, and this is quite clear, to me at least, reading your posts above. I'm saying that future theories may or may not come out to replace the existing ones does not imply that FTL will ever be possible, whereas you seem to be implying that because we know so little, FTL is possible. It is not known whether it's possible, which is what I'm trying to get at.

I used the Earth is round analogy because you seem to have wanted to show that future theories might change the way we see things, which is true, but I wanted to point out that it could've been any other possibility - it wasn't inevitable that it was going to be a sphere, and putting it into the context of the discussion above, you've neglected the possibility that FTL is impossible in our universe, since you're constantly pushing the 'FTL may be impossible in current theories, but who knows if it's possible in some future theory?' aspect. It may end up to always being impossible.

I'm not saying you should confine yourself to available theories, but what about my fairy/angels theory? I understand that you're inspired by science fiction, and it would indeed be nice to have it come true, it may end up being impossible in the end after all, which is the thing I'm trying to bring into the discussion. Sure, imagine away, but do realise that it may end up impossible in the end, because from what I'm reading of your posts, you seem to only consider/bring up that possibility in future theories without mention that it need not appear in any future theories.

And yes, this wasn't specifically tailored at you alone, which is why you won't recognise some of the things I mentioned above. Rather, this is a general critique about what I've seen in this forum from plenty of participants who love talking about things that are taken for granted in science fiction, e.g. very fast travel between stars, and dreaming up miraculous solutions to problems, and they talk as though it is an inevitability - but they're assuming such a solution exists, when that hasn't even been shown yet.

This post has been edited by bgeh: Dec 23 2009, 11:49 PM

kmarc, thanks for your generous comments. I share your appreciation about how much there is to wonder about the universe, which is why I ended up embarking on this path myself. It is indeed a pity that both of us will never be able to live long enough to see more wonderful discoveries, but we do our best in the time we're given.

The reason for this extremely late post is for me to post an example that I couldn't recall at the time of our discussion, but which suddenly hit me, where an experimental discovery could've implied something radically different that would've shaken, if not smash the foundations of physics, but the physicists knew better and posited another possibility instead, and I'd like to draw parallels with the FTL discussion we had to just highlight how 'strong' the foundations are:

It pertains to the discovery of the neutrino. When experiments measuring beta decay were started, say of tritium (likely not the substance they used), a startling discovery was made. You could measure the mass of the initial and final nuclei, and we knew the mass of the electron to quite some precision at the time. Since the mass of the nuclei >> mass of the electron, it was safe to expect that the kinetic energy of the electron to be very high, and measurements were made of it. By conservation of mass-energy, the expectation was that since we knew the initial and final masses of the particles, we'd easily be able to calculate the kinetic energy of the electron, and measurements of the kinetic energy would clump around this calculated value (looking something like a shifted delta function, something like this: __|__, with the peak at the calculated value of the expected KE). Except that they saw this instead:



That was strange, because what you had was conservation of momentum being violated. You could have gone on to interpret this as conservation of momentum being wrong, but what the physicists did was to suggest that there was another particle carrying away the extra energy and momentum - the neutrino. Remember, the neutrino is extremely hard to find, and indeed, it took another 2.5 decades before an experimental verification was even achieved.

All I'm saying is there are sound reasons for today's theories, and while they're incomplete (and possibly always will be), it doesn't mean that the foundations are automatically wrong and need overhaul, because they have managed to describe a large set of observations we've carried out so far, and any new set of foundations will always need to be able to replicate this success, and then build even more upon them.


and azerroes: there is no friction in space...

This post has been edited by bgeh: Feb 18 2010, 10:45 AM