Looking Back in Time > General Discussion

Posted: 7/7/2012 10:46:30 AM EDT

A Cosmic Speed Limit

The velocity
of light plays a central role is astronomy and in physics.
According
to the Einstein's Theory of Relativity, nothing in our universe can
exceed the velocity of light; thus, it is a kind of cosmic speed limit against
which all other velocities may be measured. More generally, light is part of
the

electromagnetic spectrum,
which includes infrared
radiation, radio waves, gamma rays, X-rays, ultraviolet radiation, and so on.
All of these are a form of light; they just have energies that differ from the
visible light that our eyes can see. Thus, these forms of
electromagnetic radiation all travel at the speed of light too.

The Speed of Light is Constant

Furthermore, contrary to normal intuition, the Theory of Relativity tells us
that light always travels at the same speed relative to some observer,
no matter what the relative motion of the observer. Thus, light emitted from a
moving airplane does not travel with the speed of light plus the speed of the
airplane, it travels with the "speed of light", no matter what the speed of the
airplane!
Although this seems strange, it has been confirmed in many
experiments. These experiments show that it is our "common sense" that is
wrong in this case!

To be precise, what we usually
call the "speed of light" is really the speed of light
in a vacuum (the absence of matter). In reality, the speed of light depends on
the material that light moves through. Thus, for example, light moves slower
in glass than in air, and in both cases the speed is less than in a vacuum.
However, the density of matter between the stars is sufficiently low that
the actual speed of light through most of interstellar space is essentially the
speed it would have through a vacuum, so we don't make much error by ignoring
the difference.

Looking Back in Time

Because light travels at a large but finite speed, it takes time for light to
cover large distances. Thus, when we see the light of very distant objects in
the universe, we are actually seeing light emitted from them a long time ago:
we see them literally as they were in the distant past.

http://csep10.phys.utk.edu/astr162/lect/cosmology/lightspeed.html

Posted: 7/7/2012 10:50:09 AM EDT

[#1]

Physics is fun

.

Posted: 7/7/2012 2:19:35 PM EDT

[#2]

Quoted:

The Speed of Light is Constant

[div]Furthermore, contrary to normal intuition, the Theory of Relativity tells usthat light always travels at the same speed relative to some observer,no matter what the relative motion of the observer. Thus, light emitted from amoving airplane does not travel with the speed of light plus the speed of theairplane, it travels with the "speed of light", no matter what the speed of theairplane! Although this seems strange, it has been confirmed in manyexperiments. These experiments show that it is our "common sense" that iswrong in this case!

The speed of light is only constand in a vacuum.

The speed of light in a refractive medium is c/i where i is the index of refraction.

The physics guys have slowed light down to less than 25 MPH for milliseconds at a time (whereas it should have gone 1K miles it traveled but a few inches.)

So, this paragraph is highly misleading.....

Posted: 7/7/2012 2:28:50 PM EDT

[#3]

Carl Sagan once said,

"Somewhere, something wonderful is waiting to be known"

I'm with him. I hope that "something" will unlock this speed limit.

Posted: 7/7/2012 2:30:42 PM EDT

[#4]

Quoted:

The Speed of Light is Constant

[div]Furthermore, contrary to normal intuition, the Theory of Relativity tells usthat light always travels at the same speed relative to some observer,no matter what the relative motion of the observer. Thus, light emitted from amoving airplane does not travel with the speed of light plus the speed of theairplane, it travels with the "speed of light", no matter what the speed of theairplane! Although this seems strange, it has been confirmed in manyexperiments. These experiments show that it is our "common sense" that iswrong in this case!

The speed of light is only constand in a vacuum.

The speed of light in a refractive medium is c/i where i is the index of refraction.

The physics guys have slowed light down to less than 25 MPH for milliseconds at a time (whereas it should have gone 1K miles it traveled but a few inches.)

So, this paragraph is highly misleading.....

Interdasting I didn't know that

Posted: 7/7/2012 2:33:31 PM EDT

[#5]

We are just vibrations of energies across the wavelengths.

Posted: 7/7/2012 2:35:06 PM EDT

[#6]

Quoted:

Carl Sagan once said,

"Somewhere, something wonderful is waiting to be known"

I'm with him. I hope that "something" will unlock this speed limit.

Maybe with the discovery of the Higgs boson someday it will

Posted: 7/7/2012 3:09:46 PM EDT

[#7]

Why does the Sun come up? Or are the stars merely pinholes in the curtain of night? Who knows?

Posted: 7/7/2012 3:22:07 PM EDT

[#8]

I've thought about this a lot. I always wondered if, faster-than-speed-of-light space travel being possible, you could travel to the far reaches of space and observe the Earths history through a ridiculously high powered telescope.

Posted: 7/7/2012 3:27:34 PM EDT

[#9]

I'm fascinated by this kind of stuff, too bad I'm too stupid to fully grasp Physics at the level I would like to.

Posted: 7/7/2012 3:30:08 PM EDT

[#10]

Quoted:
Why does the Sun come up? Or are the stars merely pinholes in the curtain of night? Who knows?

Sometimes I have looked up at the morning sky, before light, when things are quiet, and often felt shortchanged at the fact that we do understand how outer space works.

I could only imagine would it would be like to be an ancient person looking up at the sky.

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A Cosmic Speed Limit

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The Speed of Light is Constant

The Speed of Light is Constant

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