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Is Faster-Than-Light Travel or Communication Possible? (1997)

math.ucr.edu

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Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#71

Post by spacehome »

tjradcliffe wrote: post #51
spacehome wrote: post #35

Earlier quoted context omitted.

Yea, but I feel it's a good heuristic, and I'd like to hold onto it. It seems like a crude, non-mathematical formulation of Solomonoff theory. Also, Ockham's razor is the best argument in support of the Multiverse view.

Ockham's razor is a terrible heuristic, and one of the reasons the Multiverse view gets so much skepticism is that Ockham's razor is the best argument for it. Consider: Ockham himself believed that "not multiplying entities beyond necessity" was an argument for the existence of God and an argument against the existence of everything else. That is, once you had an omnipotent god, everything else was just a product of…

I agree with some of what you said, but Bayes' Rule by itself will never give you priors. Regardless of it's unfortunate origins, the way that Ockham's razor is used now in common language is a way to give approximate qualitative priors.

Also, if you don't have enough mathematics to understand ellipses, then ellipses are quite complicated. I'm comfortable with ellipse-based theories needing additional evidence in this case.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#72

Post by joshuahutt »

Udo wrote: post #45
Ono-Sendai wrote: post #44

Earlier quoted context omitted.

Ok. When you say 'how fast an object moves through time', you mean 'how fast time passes for a moving object, as seen from the inertial reference frame of another object'. I regard objects as moving at the same speed through time - 1 second per second.

It's of course a matter of taste what expression sounds more fitting to you, precisely because time is such a fluid concept. Personally, when I think about a neutrino for example, I'd say that neutrinos go crazy fast , and they experience time unimaginably slowly , so it feels more natural for me to think that velocity and time are tradeoff values of each other.

Wouldn't it be more accurate to say that neutrinos experience time normally, but observe everything else to be unimaginably slow?

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#73

Post by joshuahutt »

EGreg wrote: post #53
TrainedMonkey wrote: post #43

Earlier quoted context omitted.

I was wrong, see edit below. No, there is still an lower limit of 4.37 years to get to alpha-centauri within any frame of reference no matter how much you accelerate within conventional space. What relativity does, is that if you travel close to speed of light time taken for the trip as measured on ship versus on earth could be different by many orders of magnitude. edit: Was wrong, as per [0] "This is something many…

Wait why can't you get under 4 years if you accelerate really fast?

Because it's 4.367 light years away [1].

[1] https://www.google.com/search?q=distance+to+alpha+centauri

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#74

Post by eli_gottlieb »

dnautics wrote: post #34
spacehome wrote: post #24

> But multiverses are entirely out of keeping with the Ockham's Razor approach to doing science, and constitute more of a popular interpretation of quantum mechanics than a serious physical theory. The multiverse is not a theory - it's a logical consequence of a simple theory. This claim is logically akin to claiming that the universe is identical to the observable universe, because to propose that matter exists outs…

remember, though that ockham's razor is not an axiom, it's a heuristic.

No, it's a necessary consequence of the fact that the observable macrostates we care about can be composed of many, many ontologically-basic microstates in any reductionist ontology. If you live in a world where large things are composed of small things that run according to fixed rules, with causality being more fundamental the further into the small you go, then any observable "question" will have low Kolmogorov complexity compared to the total information necessary to write down the exact micro-state of the system you're asking the question about, which means simpler "questions" or "concepts" will capture larger portions of the fundamental particles' configuration-space.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#75

Post by Ono-Sendai »

pdonis wrote: post #61
Ono-Sendai wrote: post #32

re: point 18: It is quite possible to get around this paradox, if you have absolute time. Absolute time means you can't send a message back in absolute time, which means you can't get 'causal loops'.

> It is quite possible to get around this paradox, if you have absolute time Which, according to our best current theories, we don't.

Well, it's important to note that special relativity doesn't say there is no absolute time, but rather that if there is, it is undetectable in any inertial reference frames.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#76

Post by shepardrtc »

pdonis wrote: post #59
Udo wrote: post #33

The consensus interpretation is that FTL is not possible in normal space, since the speed of something is just another way of looking at how "fast" it travels through time - FTL becomes impossible by definition. However, there is reason to assume a lot of things may be going on that are not strictly speaking taking place in normal flat space. The article mentions the expansion of the universe as an example, and that'…

> The consensus interpretation is that FTL is not possible in normal space I don't think this really makes sense, because "normal space" is not a well-defined term. What our current relativistic theories say is that spacetime contains a causal structure marked out by light cones, and nothing can move outside the light cones. In certain spacetimes (like the one that describes our expanding universe), it is possible to…

> According to our current theories, any such manipulations would require what is called "exotic matter".

Fun read:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011001...

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#77

Post by pdonis »

Ono-Sendai wrote: post #75
pdonis wrote: post #61

Earlier quoted context omitted.

> It is quite possible to get around this paradox, if you have absolute time Which, according to our best current theories, we don't.

Well, it's important to note that special relativity doesn't say there is no absolute time, but rather that if there is, it is undetectable in any inertial reference frames.

> special relativity doesn't say there is no absolute time, but rather that if there is, it is undetectable in any inertial reference frames.

No, SR says there is no absolute time, because such a thing is undetectable in any inertial reference frame. The theory that makes all the same predictions as SR, but also says that there is such a thing as "absolute time", but it's undetectable in any inertial reference frame (so it doesn't change any experimental predictions), is Lorentz Ether Theory (LET), not SR.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#78

Post by Ono-Sendai »

pdonis wrote: post #77
Ono-Sendai wrote: post #75

Earlier quoted context omitted.

Well, it's important to note that special relativity doesn't say there is no absolute time, but rather that if there is, it is undetectable in any inertial reference frames.

> special relativity doesn't say there is no absolute time, but rather that if there is, it is undetectable in any inertial reference frames. No, SR says there is no absolute time, because such a thing is undetectable in any inertial reference frame. The theory that makes all the same predictions as SR, but also says that there is such a thing as "absolute time", but it's undetectable in any inertial reference frame…

My understanding is that SR doesn't go quite as far as saying 'there is no absolute time', rather it dismisses the concept as undetectable and unnecessary (and useless).

In other words, it doesn't disprove absolute time, it just dispenses with it.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#79

Post by EGreg »

joshuahutt wrote: post #73
EGreg wrote: post #53

Earlier quoted context omitted.

Wait why can't you get under 4 years if you accelerate really fast?

Because it's 4.367 light years away [1]. [1] https://www.google.com/search?q=distance+to+alpha+centauri

But from the point of view of the traveler, it an take far less time.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#80

Post by ikeboy »

gizmo686 wrote: post #62
ikeboy wrote: post #57

Earlier quoted context omitted.

Can you continuously accelerate at g for 50 years without going over the speed of light? According to wolfram alpha http://www.wolframalpha.com/input/?i=speed+of+light%2Flittle... it would take a year to get to the speed of light at 1g (if my equation was right.) Then you can't speed up anymore.

Your equation is correct in a Newtonian universe, but does not consider relativistic effects. Generally when we talk about an object's acceleration, we are talking about its acceleration in its own reference frame. By definition, an object's velocity in its own reference frame is always 0, so acceleration does not become more difficult (ignoring the fact that the surrounding matter will be impacting you at higher spe…

So why is it difficult to maintain a constant acceleration? Is 1g really that impractical right now?
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