Freethought & Rationalism Archive

John Page · 01-09-2003, 09:04 AM

If we could not sense the electromagnetic spectrum and had not discovered its phenomena, would we have concluded through a theory of relativity that nothing could exceed the speed of sound?

I'm trying to get my mind round this hypothetical question that occured to me after reading the latest experiment that supposedly proves the speed of gravity is near the speed of light by measuring light distortion round Jupiter (Washington Post, Jan 7 2003)

Thoughts? Cheers, John

Asha'man · 01-09-2003, 09:40 AM

Nah, if we couldn't experience the electromagnetic spectrum, I don't think we would ever have come up with the Theory of Relativity. We would be permanently stuck with Newtonian Mechanics, since it would appear to apply in every situation we could possibly observe (touch?).

Silent Acorns · 01-09-2003, 10:15 AM

There is absolutely no way that we would ever have developed a theory of realativity based on the speed of sound. The physics behind the speed of light and the speed of sound are completely different from each other.

Andrew · 01-09-2003, 11:22 AM

See, I know that light is supposed to be the speed limit of the universe and all, but, even though I've read some on it, I still don't really get it.

Mageth · 01-09-2003, 11:47 AM

Silly me, I didn't know that gravity had a speed!

Here's a link to an article on the experiment that John Page referred to. Apparently there are some criticizing the experiment, so I don't think it's yet been accepted as definitive.

From this article on the speed of gravity (by Tom Van Flandern), the speed of gravity is >= (2x10^10 c).

Any physicists around who can explain this astronomical discrepancy???

cfgauss · 01-09-2003, 12:30 PM

(I'm a physicist!! Well, a theoretical physics major anyway)
The speed of gravity, as predicted by general relativity, is the speed of light. If it wasn't (or at least close to it), then GR wouldn't work. Since GR does, it is.

And it's easy enough to see why the speed of light is the "speed limit" for the universe. Remember that the speed of light is always the same, (i.e., isotropic) regardless of velocity. So, you should be able to see conceptual problems with going faster than light, but light still going the speed of light, according to you. If you'd like, I can show you why more rigorously (it's actually pretty simple, it involves no more than some algebra and a few pretty pictures) why c is the upper limit.

Andrew · 01-09-2003, 12:33 PM

Sure, why not?

If it's the old 'flashlight and spaceship' thing, though, I've heard that one before. I just don't understand why it works, though.

Mageth · 01-09-2003, 12:52 PM

Thanks, cfgauss. I was happily getting along on the assumption that gravitational effects were essentially instantaneous. I read through most of Van Flandern's paper and he seemed to make a pretty good case for the much higher "speed" of gravity, but not being a physicist I can't vouch for my critical judgment on his arguments. What is your take on that paper?

cfgauss · 01-09-2003, 01:44 PM

The "flashlight and spaceship" argument is the best way to explain it, although some people manage to butcher the explanation and only confuse everyone. I tried the best I could to make it clear and understandable, although I haven't had time to proofread it or spell check it yet!
http://home.attbi.com/~cfgauss/relativity.htm

Regarding that site, it looks like it's just crap, check out some of their other articles:
http://www.metaresearch.org/solar%20...iles/proof.asp
I was going to post more, but just reading some of the titles made me stupider, and I wouldn't want to subject anyone to their contents.
And, as a general rule of thumb, if someone contradicts something explicitly predicted by relativity, they're wrong; if someone contradicts empirical reality, they're wrong and full of crap.

Mageth · 01-09-2003, 01:59 PM

Regarding that site, it looks like it's just crap, check out some of their other articles:

Ugh, the article you posted to is definitely crap. And the article I posted may well be crap, but note that it's a fallacy to assume its mere presence on a website that has other "crap" articles makes it so. So I think the article must be addressed on its own merits.

(Note that the abovenoted experiment, other previous measurements, and the GR theory combine to convince me for now that the speed of gravity is indeed near the speed of light.)

01-09-2003, 09:04 AM	#1
John Page Veteran Member Join Date: May 2001 Location: US Posts: 5,495	How relative is speed? If we could not sense the electromagnetic spectrum and had not discovered its phenomena, would we have concluded through a theory of relativity that nothing could exceed the speed of sound? I'm trying to get my mind round this hypothetical question that occured to me after reading the latest experiment that supposedly proves the speed of gravity is near the speed of light by measuring light distortion round Jupiter (Washington Post, Jan 7 2003) Thoughts? Cheers, John

01-09-2003, 09:40 AM	#2
Asha'man Veteran Member Join Date: Dec 2001 Location: southeast Posts: 2,526	Newton rules! Nah, if we couldn't experience the electromagnetic spectrum, I don't think we would ever have come up with the Theory of Relativity. We would be permanently stuck with Newtonian Mechanics, since it would appear to apply in every situation we could possibly observe (touch?).

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01-09-2003, 10:15 AM	#3
Silent Acorns Veteran Member Join Date: Oct 2002 Location: SW 31 52 24W4 Posts: 1,508	There is absolutely no way that we would ever have developed a theory of realativity based on the speed of sound. The physics behind the speed of light and the speed of sound are completely different from each other.

01-09-2003, 11:22 AM	#4
Andrew Junior Member Join Date: Jan 2003 Location: UK Posts: 11	See, I know that light is supposed to be the speed limit of the universe and all, but, even though I've read some on it, I still don't really get it.

01-09-2003, 11:47 AM	#5
Mageth Contributor Join Date: Jul 2001 Location: Deep in the heart of mother-lovin' Texas Posts: 29,689	Silly me, I didn't know that gravity had a speed! Here's a link to an article on the experiment that John Page referred to. Apparently there are some criticizing the experiment, so I don't think it's yet been accepted as definitive. From this article on the speed of gravity (by Tom Van Flandern), the speed of gravity is >= (2x10^10 c). Any physicists around who can explain this astronomical discrepancy???

01-09-2003, 12:30 PM	#6
cfgauss Regular Member Join Date: Jan 2003 Location: USA Posts: 108	(I'm a physicist!! Well, a theoretical physics major anyway) The speed of gravity, as predicted by general relativity, is the speed of light. If it wasn't (or at least close to it), then GR wouldn't work. Since GR does, it is. And it's easy enough to see why the speed of light is the "speed limit" for the universe. Remember that the speed of light is always the same, (i.e., isotropic) regardless of velocity. So, you should be able to see conceptual problems with going faster than light, but light still going the speed of light, according to you. If you'd like, I can show you why more rigorously (it's actually pretty simple, it involves no more than some algebra and a few pretty pictures) why c is the upper limit.

01-09-2003, 12:33 PM	#7
Andrew Junior Member Join Date: Jan 2003 Location: UK Posts: 11	Sure, why not? If it's the old 'flashlight and spaceship' thing, though, I've heard that one before. I just don't understand why it works, though.

01-09-2003, 12:52 PM	#8
Mageth Contributor Join Date: Jul 2001 Location: Deep in the heart of mother-lovin' Texas Posts: 29,689	Thanks, cfgauss. I was happily getting along on the assumption that gravitational effects were essentially instantaneous. I read through most of Van Flandern's paper and he seemed to make a pretty good case for the much higher "speed" of gravity, but not being a physicist I can't vouch for my critical judgment on his arguments. What is your take on that paper?

01-09-2003, 01:44 PM	#9
cfgauss Regular Member Join Date: Jan 2003 Location: USA Posts: 108	The "flashlight and spaceship" argument is the best way to explain it, although some people manage to butcher the explanation and only confuse everyone. I tried the best I could to make it clear and understandable, although I haven't had time to proofread it or spell check it yet! http://home.attbi.com/~cfgauss/relativity.htm Regarding that site, it looks like it's just crap, check out some of their other articles: http://www.metaresearch.org/solar%20...iles/proof.asp I was going to post more, but just reading some of the titles made me stupider, and I wouldn't want to subject anyone to their contents. And, as a general rule of thumb, if someone contradicts something explicitly predicted by relativity, they're wrong; if someone contradicts empirical reality, they're wrong and full of crap.

01-09-2003, 01:59 PM	#10
Mageth Contributor Join Date: Jul 2001 Location: Deep in the heart of mother-lovin' Texas Posts: 29,689	Regarding that site, it looks like it's just crap, check out some of their other articles: Ugh, the article you posted to is definitely crap. And the article I posted may well be crap, but note that it's a fallacy to assume its mere presence on a website that has other "crap" articles makes it so. So I think the article must be addressed on its own merits. (Note that the abovenoted experiment, other previous measurements, and the GR theory combine to convince me for now that the speed of gravity is indeed near the speed of light.)

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