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Author Topic: Faster than the speed of light?  (Read 5060 times)

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Offline mcgillca

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Re: Faster than the speed of light?
« Reply #15 on: 17:31:55, 05 August, 2013 »
Whilst you are right that space is not a vacuum, actually light always travels at the speed of light, even in a denser medium like glass.

As I understand it, a photon would interact with the electrons in the glass. After a short while, another photon would be re-emitted with the same energy and momentum (conservation of momentum and energy). This would keep happening throughout the glass. In between interactions with electrons, the photons travel at the speed of light. It is the slight delay in the absorption and re-emission which slows the process down and makes the light appear to have a velocity of less than c. See e.g. http://www.physicsclassroom.com/class/refrn/u14l1d.cfm

As for the practical consideration, the average density of space is about 1 hydrogen atom per m^3. A photon can go a very long way without hitting an electron, so suspect that the speed of light in space is very, very close to the theoretical maximum!

Colin
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Re: Faster than the speed of light?
« Reply #16 on: 18:54:14, 05 August, 2013 »
Therefore the entire universe may be many, many times larger than what we can observe, or will ever be able to observe!

I'm not sure I agree with this. As the age of the universe is supposed to be  touch under 14 billion years, and the most distant observed objects are a bit over 13 billion light years away, one feels we've seen quite a bit of it.

Granted, during the inflationary period the expansion exceeded the speed of light, but this was a short lived period. I don't think it was enough to make the universe "many times larger" that that which we can observe.
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Offline markthais

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Re: Faster than the speed of light?
« Reply #17 on: 07:56:21, 27 August, 2013 »
http://www.photonicsonline.com/doc/researchers-slow-light-to-a-crawl-in-liquid-crystal-matrix

well Colin, The physicsclassroom is a nice example but it is wrong. There example of an nonmass objective moving a mass objective is a nice Newtonian explanation.
Check out the Photonics article. Light travels is wave packets and as they leave the medium they reassemble  back to the wave.
But my original argument still holds that  the new medium is not a pure vacuum, so it is not at C. If we add that a photon has the smallest amount of mass, it doesn't matter how small, then it changes all are theories of relativity.
It is funny that they looked for (aether) and now we are looking for dark matter to explain why the galaxies don't have enough matter. If  you replace the names you can come up with the sames answers that relativity shows. If there is a undetectable medium that light needs to travels through. This will create a whole lot of new what if. 
Something to think about.
Mark         

Offline markthais

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Re: Faster than the speed of light?
« Reply #18 on: 07:26:53, 12 September, 2013 »
Colin, I though you where my friend  Colin from California. So If I come off arrogant, it was because I though you where him. It is good to question the theories because that is all they are.
In solar physics what was taught 40 years ago have been shown to be wrong. With better equipment they are finding more questions and no models to put them in.
This is the world of physics.
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Offline aerodda

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Re: Faster than the speed of light?
« Reply #19 on: 20:00:02, 07 October, 2013 »

Cosmological expansion is roughly 3.53 times the speed of light.  Nothing is actually travelling faster than the speed of light, its the actual fabric of space that's expanding.  The gravity in our solar system and galaxy overcomes this Cosmological effect on 'small' scales.

The big bang was, perhaps, homogeneous but small over-densities caused by local gravitational fluctuations were magnified during the 'inflation' described by Alan Guth.  These over/under-densities are seen in the CMB and as the universe expanded became matter/dark-matter haloes from which galaxies formed.  That's why the CMB is so important.

There's nothing at the 'edge' of space.  It isn't geometrically flat.  It's curved in more than three dimensions and 'stuff' travels on geodesics.  (The curved space equivalent of straight lines).  So if you set off in a straight line you'd eventually come back to where you started.  Think of it as a bit like explaining a 'round' Earth in a three dimensional world to someone in the middle ages.

regards

Tony


Offline Trow

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Re: Faster than the speed of light?
« Reply #20 on: 14:52:19, 10 December, 2013 »
IF you agree with expansion, you ARE ABSOLUTELY saying things are travelling faster than the speed of light.

If 2 things are farther apart from each other today than they were yesterday then energy must have been spent. If they are moving apart faster than C then you must need more energy than is possible. I can see how you explain expanding space, I just don't think galaxies would move with it.

That's why I chose to believe in shrinking matter - if 2 things are smaller than they were yesterday they will appear farther apart (if everything shrinks at the same rate, the measurements that are made shrink too). I'm not suggesting anything is added or subtracted from the mass, just that atoms take up less room (and so space seems bigger). I'm sure this does break plenty of other rules of which I am currently ignorant, but, until then, I can get some sleep continuing to hold on to this deeply unpopular view.
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Offline mcgillca

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Re: Faster than the speed of light?
« Reply #21 on: 15:43:41, 10 December, 2013 »
I remember being asked this during my university interview - if the mass of the electron increased by a factor of 10 overnight (thus shrinking all matter), how would you know, given that rulers would also shrink.

The answer was that the distance to heavenly bodies would not shrink, so they would appear smaller.

Given that this has not been observed, you would have to dream up a strange mechanism that shrank galaxies, but not the sun and moon!

Colin
Main scope: Ikharos 8" RC
Camera: Atik 460ex with Atik EFW and Baader LRGB Ha, OIII and SII filters
Guide scope: On Axis Guider with Atik 314L+
Mount: Paramount MX located in Astrocamp, Nerpio, Spain

Offline MikeDunn

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Re: Faster than the speed of light?
« Reply #22 on: 20:48:14, 10 December, 2013 »
IF you agree with expansion, you ARE ABSOLUTELY saying things are travelling faster than the speed of light.
Not necessarily ...

Assume I am at a point B that is midway between an object at point A and an object at point C.  If an object at points A and C started to recede from me at 0.75c, then they recede from me under the speed of light, yes ?  If you are at point A, I am receding at 0.75c from you, but the object that was at point C is now apparently receding at 1.5c.

Except it isn't, is it.
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Offline Trow

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Re: Faster than the speed of light?
« Reply #23 on: 17:22:03, 28 December, 2013 »
In the model I'm think of everything in a gravitational field would be shrinking proportionately - galaxies, galaxy clusters, solar systems, atomic structure, etc. The Earth shrinks, the Moon shrinks and the distance between them shrinks. From inside the system, nothing has changed, our only perception is that other galaxies are getting further away. Is this any more challenging than the paradigm view where space is expanding carrying galaxies with it faster than the speed of light requiring mind-bending amount of energy.

Also, if atomic orbits were decreasing over time, would the wavelength of light be decreasing? This again would be imperceptible locally, but, would result in a redshift that would be more pronounced the longer ago the light was emitted as is observed the more distant a galaxy is form us?
Bresser 8" f4.3 Newt, CGEM, unbranded Chinese digital eyepiece.

Expanding Universe denier.

Offline MikeDunn

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Re: Faster than the speed of light?
« Reply #24 on: 17:37:09, 28 December, 2013 »
Surely the gravitational field would be attractive, so they'd get closer ...
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Offline Trow

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Re: Faster than the speed of light?
« Reply #25 on: 13:52:02, 03 March, 2014 »
Yes, but proprtianately smaller.
Bresser 8" f4.3 Newt, CGEM, unbranded Chinese digital eyepiece.

Expanding Universe denier.

 

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