Originally posted by avalanchethecat According to this article (http://www.scientificamerican.com/article.cfm?id=misconceptions-about-the-2005-03) Special Relativity does forbid objects from having a relative velocity in excess of that of light. They sound like they know what they're talking about.
Can you quote the relevant part please?
According to SR objects that are massive and start with v<c always travel with v<c.
According to SR if you add v1,v2 (with v1<c and v2<c) the final v always is v<c.
But nothing in SR forbids bodies of having v>c. That's just a misconception and I could link you to a thousand articles on arXiv showing you that.
Originally posted by adam warlock Can you quote the relevant part please?
According to SR objects that are massive and start with v<c always travel with v<c.
According to SR if you add v1,v2 (with v1<c and v2<c) the final v always is v<c.
But nothing in SR forbids bodies of having v>c. That's just a misconception and I could link you to a thousand articles on arXiv showing you that.
I'm gonna admit here that I'm not actually a physicist! It is my understanding from reviews of this article that my previous assertion holds, but having examined it fairly closely I can't determine this for sure. If you like, you can check the article yourself without going via Scientific American by searching for Charles H. Lineweaver and Tamara M. Davis and downloading the PDF, 'cos I'll be honest, you also sound like you know what you're talking about!!
Originally posted by avalanchethecat I'm gonna admit here that I'm not actually a physicist! It is my understanding from reviews of this article that my previous assertion holds, but having examined it fairly closely I can't determine this for sure. If you like, you can check the article yourself without going via Scientific American by searching for Charles H. Lineweaver and Tamara M. ...[text shortened]... ing the PDF, 'cos I'll be honest, you also sound like you know what you're talking about!!
Thanks. I'm on arXiv right now and reading their article: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf (for those that also want to check it out)
By the way: how much mathematically proficient are you?
Originally posted by adam warlock Thanks. I'm on arXiv right now and reading their article: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf (for those that also want to check it out)
By the way: how much mathematically proficient are you?
From the abstract:
We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light.
Originally posted by adam warlock From the abstract:
[b]We show that we can observe galaxies that have
, and always have had, recession velocities greater than the speed of light.
[/b]Isn't the concept here that nothing is travelling through space faster than light (so special relativity is still OK), but that space itself is expanding? Or is that too simplistic?
Originally posted by adam warlock Thanks. I'm on arXiv right now and reading their article: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf (for those that also want to check it out)
By the way: how much mathematically proficient are you?
We...eelll, it took me a couple of years to get through 'The Road To Reality', but I did in the end. With a bit of a leg-up here and there. So not great, but no idiot either.
Originally posted by amolv06 From what I've heard, special relativity doesn't forbid faster than light travel, it only forbids travelling at the speed of light. I often hear people say that if one was to travel faster than light, one would go backwards in time. Where does this assertion come from? To me, it seems like that rather than going backwards in time, one would move in a sort of imaginary time dimension. What am I missing here?
Gravitons travel faster than light. This idea that things can't travel faster than light is so 20th Century thinking...
Originally posted by mtthw Isn't the concept here that nothing is travelling through space faster than light (so special relativity is still OK), but that space itself is expanding? Or is that too simplistic?
That's it. But the fact that space is expanding has consequences on a physical level.
Originally posted by avalanchethecat We...eelll, it took me a couple of years to get through 'The Road To Reality', but I did in the end. With a bit of a leg-up here and there. So not great, but no idiot either.
That's a great book. If you've read it that in principle you already know a lot about physics and the mathematics needed to understand it.
But the reason I've asked you that is that I wanted to link you an article from arXiv where SR is derived (by Feigenbaum) using only the principle of relativity.
It is a long and at points heavy article but is extremely elegant: http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1234v1.pdf
Originally posted by adam warlock That's a great book. If you've read it that in principle you already know a lot about physics and the mathematics needed to understand it.
But the reason I've asked you that is that I wanted to link you an article from arXiv where SR is derived (by Feigenbaum) using only the principle of relativity.
It is a long and at points heavy article but is extremely elegant: http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1234v1.pdf
That is indeed a hefty old paper, I may have a close look later, though I suspect I may need some help with the math! I scanned the conclusion though - is he actually suggesting that photons might have mass? That's gotta be contentious. Seems rather brilliant if he's genuinely deriving SR from Gallileo's work alone.
Originally posted by avalanchethecat That is indeed a hefty old paper, I may have a close look later, though I suspect I may need some help with the math! I scanned the conclusion though - is he actually suggesting that photons might have mass? That's gotta be contentious. Seems rather brilliant if he's genuinely deriving SR from Gallileo's work alone.
His insight is a rather deep one (although strictly speaking others have hinted into it before): imagine that you have three inertial frames A, B and C. Imagine also that you go from A to B with a boost and that you go from B to C with another boost. Mathematically speaking you have no right to assert that after these boosts the axis from the A frame and the axis from the C frame are still aligned. The is a "rotation" matrix that allows you to go from A to C. If this matrix is the identity matrix you have Newtonian mechanics but if this matrix isn't the identity you have SR.
As for the hypothesis that photons may have mass. In this new framework it is perfectly possible for photons to have mass and it is a matter of experiment to decide if they have or have not (a gross oversimplification, but...).
To tell you the truth some people were doing experiments in the past to see if the photon is indeed massless or not. The results are that the photon are massless within experimental erros as far as I know.
Edit: After that some other Russian guys have extended his result. They showed that by assuming that translations need not to be commutable you arrive at GR. Now that's something!
Faster than light
27 Apr '10 21:26
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