C, is it a constant?

Singular Quartet · Post by **Singular Quartet** » 2003-01-22 10:35pm

Soemone mentioned earlier that different wavelengths of light move at different speeds. IIRC, isn't that the basis for Red Shift?

Crown · Post by **Crown** » 2003-01-22 10:37pm

That was me, and as I said dis-regard the post. I can't remember the details and I can't find the article in question, I was just hoping it would jog someone's memory in case they came across the same article...

Durandal · Post by **Durandal** » 2003-01-23 12:14am

Singuler Quartet wrote:Soemone mentioned earlier that different wavelengths of light move at different speeds. IIRC, isn't that the basis for Red Shift?

No. Light loses energy as it travels, but it does not slow down. As light's wavelength increases due to the energy decrease, its frequency decreases, so as to keep the relationship

c = (lambda)*(frequency).

Joe Richter · Post by **Joe Richter** » 2003-01-23 10:26am

[quote="NF_Utvol"]If that is true, that would completely destroy Einstein's Theory Of Relativity, which assums that C is a constant. And, as you know, the Theory of Relativity, is a cornerstone of modern physics. This would make the majority of things in most Physics textbooks wrong, and therefore, would have to be re-written.quote]

Youknow, Einsteins theory or relativity was shown to have greater predictive powers than Newtons laws of motion. Did this meen that they all had to be scraped? No. All it ment was that it was acknowledged that newtons laws could not be applied in all circumstances. The same has happened with general relativity with the advent of quantum theory. Relativity has been proven to have accurate predictive powers (as someone has already posted) so it CAN'T be wrong on anywere the level you seem to be sugesting.

Nathan F · Post by **Nathan F** » 2003-01-23 02:08pm

As previously stated, I am not suggesting it is wrong. BUT if it was PROVEN to be wrong, then, well, it would have to be done away with. The likelyhood of this happening is very small though, as it is so established, and has lasted this long without being proven wrong, so it will take a major breakthrough to do that.

Post by **Darth Wong** » 2003-01-23 02:14pm

NF, you're still not getting it. Theories aren't either "true or false", they are more or less accurate. Theories are predictive models, like curve-fits for a set of data points. A theory which produces an excellent curve-fit is always going to be a good and useful theory, even if one can be produced which is even better. A theory which is completely fucked up, however (like the "big changes in c" theory, which can't explain even the appearance of whole galaxies) is simply useless.

I strongly suggest that if you intend to become an engineer as you've said, that you learn to avoid the black/white fallacies that plague creationist thinking when they seek to attack theories by showing that they are not perfect, rather than showing that they've got a more accurate one.

Post by **Darth Wong** » 2003-01-23 02:16pm

PS. Or, to put it another way, it is possible to say that a theory is garbage if it is way off the mark. But if a theory is extremely accurate yet not perfect, it would be ludicrous to say the same.

Cthulhu-chan · Post by **Cthulhu-chan** » 2003-01-23 02:55pm

Yo, don't know if you all heard, but the peer reviews on the "speed of gravity" experiment are looking unfavorable.

http://www.newscientist.com/news/news.jsp?id=ns99993282

T'would appear that the propigation speed of gravity may remain a mystery for now.

Post by **Lagmonster** » 2003-01-23 03:01pm

Cthulhu-chan wrote:Yo, don't know if you all heard, but the peer reviews on the "speed of gravity" experiment are looking unfavorable.

Here's the abstract of the criticism from Will's paper:

We calculate the delay in the propagation of a light signal past a massive body that moves with speed v, under the assumption that the speed of propagation of the gravitational interaction c_g differs from that of light. Using the post-Newtonian approximation, we consider an expansion in powers of v/c beyond the leading "Shapiro" time delay effect, while working to first order only in Gm/c^2, and show that the altered propagation speed of the gravitational signal has no effect whatsoever on the time delay to first order in v/c beyond the leading term, although it will have an effect to second and higher order. We show that the only other possible effects of an altered speed c_g at this order arise from a modification of the parametrized post-Newtonian (PPN) coefficient \alpha_1 of the metric from the value zero predicted by general relativity. Current solar-system measurements already provide tight bounds on such a modification. We conclude that recent measurements of the propagation of radio signals past Jupiter are sensitive to \alpha_1, but are not directly sensitive to the speed of propagation of gravity.

The PDF can be read here, but be warned, it's not for kids: http://arxiv.org/PS_cache/astro-ph/pdf/0301/0301145.pdf

Nathan F · Post by **Nathan F** » 2003-01-23 03:47pm

Darth Wong wrote:PS. Or, to put it another way, it is possible to say that a theory is garbage if it is way off the mark. But if a theory is extremely accurate yet not perfect, it would be ludicrous to say the same.

I see what you mean. Like alot of things, this is one that, as long as it is really really really close, then it will work. When something has such a small difference as this would, it probably wouldnt make much of a difference in any calculations. It would be like saying that if the earth's orbit was extened out by an inch, it most likely would never be noticed on the surface.

I am also saying that, if this did turn out to be true, then the theory of relativity, which assumes that C is a constant, would TECHNICALLY, but not necessarily practically, be obsolete.

Ugh, this is the reason that I would like to be an engineer. You never have to deal with infinites and crap like this, its all stuff you can touch...

I think too linearly! lol (linearly, is that a word?)

Also, I am interested in learning more in the background of the theory of relativity, specifically, what are the reasons for saying that at the speed of light, matter turns to energy. Can anybody point me to some readings on this, online or paper?

Post by **Darth Wong** » 2003-01-23 04:00pm

How could the theory of relativity be obsolete if it has not been replaced by an improved theory?

This is not new; the theory of relativity cannot explain behaviour of matter at quantum scales; we have known this since before any of us were born. But that does not make it "obsolete"; it still works and we have yet to come up with something better.

Look at time dilation, mass dilation, etc. These effects have all been observed. If you disregard the theory of relativity or consider it obsolete, then you must explain these phenomena WITHOUT it.

Relativity is used in the engineering of particle accelerators. When a theory is reliable enough to be used for engineering purposes, let's just say that it's pretty damned good. I haven't seen any replacement yet; have you?

Nathan F · Post by **Nathan F** » 2003-01-23 04:05pm

I am not saying that E=mc^2 is obsolete. And as you stated earlier, it is the best thing we have going right now. I was just saying that if it was proven to be erroneous, which I seriously doubt will happen, then it would become, as stated earlier, technically, but not practically, obsolete. I am not saying it is obsolete now, as it isn't, and the odds of it becoming obsolete within any of our lifetimes is nearly nil.

Durandal · Post by **Durandal** » 2003-01-23 04:17pm

NF_Utvol wrote: Ugh, this is the reason that I would like to be an engineer. You never have to deal with infinites and crap like this, its all stuff you can touch...

I think that engineers are masochists, personally. Every little thing must be taken into account, and you can't ignore friction or air resistance, which sucks because you have to be exactly correct. Meanwhile, in astronomy/cosmology, your answer is considered valid as long as you fall in the accepted order of magnitude!

I think too linearly! lol (linearly, is that a word?)

Yes.

Also, I am interested in learning more in the background of the theory of relativity, specifically, what are the reasons for saying that at the speed of light, matter turns to energy. Can anybody point me to some readings on this, online or paper?

If you're studying to be an engineer, chances are you'll be taking a physics sequence somewhat similar to what I'm taking. Your second-level physics textbook should include some stuff about special and general relativity. Or you could do what I did and take a graduate-level cosmology course your freshman year.

Seriously though, get your basic down cold. Get your maths down, as well -- this shouldn't be too hard, though. As you take higher level math courses, your existing skills will be refined and improved (my algebra and trigonometry skills improved by leaps and bounds when I took first-level calculus). If you really want to understand relativity, you'll need more than single-variable calculus; you'll need differential equations and multi-variable calculus, as well as linear algebra. You'll also need thermodynamics and wave physics.

Basically, don't try to walk before you can crawl.

johnmarkley · Post by **johnmarkley** » 2003-01-23 04:25pm

The constant is not the speed of light, but the speed of light through a vacuum. Light travels at different speeds through different mediums; we've known this for a long time, now. Scientists have been able to completely stop it by passing it through a Bose-Einstein condensate.

What's that made of?

Durandal · Post by **Durandal** » 2003-01-23 04:35pm

johnmarkley wrote:
The constant is not the speed of light, but the speed of light through a vacuum. Light travels at different speeds through different mediums; we've known this for a long time, now. Scientists have been able to completely stop it by passing it through a Bose-Einstein condensate.
What's that made of?

It's a state of matter in which all bosons (mediating particles) exist in the same quantum state, thus forming a sort of super-atom, composed of many atoms, but the whole lot of them act as though they were all one atom.

Nathan F · Post by **Nathan F** » 2003-01-23 04:46pm

What are you studying, Durandal?

Howedar · Post by **Howedar** » 2003-01-23 04:47pm

Durandal wrote:
Singuler Quartet wrote:Soemone mentioned earlier that different wavelengths of light move at different speeds. IIRC, isn't that the basis for Red Shift?
No. Light loses energy as it travels, but it does not slow down. As light's wavelength increases due to the energy decrease, its frequency decreases, so as to keep the relationship

c = (lambda)*(frequency).

I believe you're wrong, and that red shifting is based entirely on an object moving away from the observer, changing its apparent frequency.

I'm no astrophysicist though.

Post by **Darth Wong** » 2003-01-23 05:00pm

NF_Utvol wrote:What are you studying, Durandal?

He's studying physics, and the mating habits of college girls.

Post by **Lagmonster** » 2003-01-23 05:04pm

Darth Wong wrote:
NF_Utvol wrote:What are you studying, Durandal?
He's studying physics, and the mating habits of college girls.

If I remember university, one moreso than the other for at least the first two years.

Post by **Darth Wong** » 2003-01-23 05:05pm

I met Rebecca in university. 'Nuff said.

Durandal · Post by **Durandal** » 2003-01-23 05:09pm

Howedar wrote:
Durandal wrote:
Singuler Quartet wrote:Soemone mentioned earlier that different wavelengths of light move at different speeds. IIRC, isn't that the basis for Red Shift?
No. Light loses energy as it travels, but it does not slow down. As light's wavelength increases due to the energy decrease, its frequency decreases, so as to keep the relationship

c = (lambda)*(frequency).
I believe you're wrong, and that red shifting is based entirely on an object moving away from the observer, changing its apparent frequency.

I'm no astrophysicist though.

If that was true, then light would be getting brighter as it approached us. Think about it. If light's wavelength relative to itself was constant, and an observer observed it as getting longer as the photon got further away, then as it got closer, the apparent wavelength should get shorter, and the apparent energy should increase. But, there is no such thing as apparent energy, and since wavelength is related to energy, there's no such thing as apparent wavelength either.

Light does lose energy as it travels, and it initially loses energy as it escapes from the gravitational field of the star which created it (if we're talking light from a star). It takes a photon literally millions of years to get from the center of a star to the surface, and they lose a lot of initial energy in that journey. Running through various gravity wells and small bumps in space on the way also costs energy. The result is a net loss in frequency and energy, i.e. a redshift.

Durandal · Post by **Durandal** » 2003-01-23 05:10pm

Darth Wong wrote:
NF_Utvol wrote:What are you studying, Durandal?
He's studying physics, and the mating habits of college girls.

I'm currently trying to get some lab time in.

Admiral Valdemar · Post by **Admiral Valdemar** » 2003-01-23 05:16pm

So does anyone think that the gravity propogation speed is more or less than c? Just to give another question.

Durandal · Post by **Durandal** » 2003-01-23 05:18pm

Admiral Valdemar wrote:So does anyone think that the gravity propogation speed is more or less than c? Just to give another question.

Einstein predicted that it propogated at c. I don't think I'm qualified to argue with him, even when he's a corpse.

Post by **Lagmonster** » 2003-01-23 05:19pm

Admiral Valdemar wrote:So does anyone think that the gravity propogation speed is more or less than c? Just to give another question.

I'm somewhat sure I dropped a link higher up in this thread to the paper that is part of the criticism to the 'gravity moves at c' discovery. Frankly, I am having a hell of a time following it. Mike would probably make more sense of the issue.

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C, is it a constant?

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