Photographing the distant past...?

This is speed of light through a vacuum that we are considering here, what if there is a nearby region of space that for some reason slows down light to a near stop. If we looked through this region at Earth we might be able to see our past without traveling FTL .

Light, which normally travels the 240,000 miles from the Moon to Earth in less than two seconds, has been slowed to the speed of a minivan in rush-hour traffic -- 38 miles an hour. An entirely new state of matter, first observed four years ago, has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super- atom with characteristics similar to a laser. Such an exotic medium can be engineered to slow a light beam 20 million-fold from 186,282 miles a second to a pokey 38 miles an hour.

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It is hard to imagine being able to resolve events on a human scale but it does seem like there are ways to beat light at its own game.

I guess this brings up the question of "does information dissipate over distance (i would say yes...laws of entropy)? How much entropy exists in informational blocks? What are the various forms of information that can exist, and how fast do they travel?

Light is only one way to encode information. There are many, many others (gravity is one that is being worked on in China with Buzz Aldrin). And I would bet that many of them would be far, far better than light at the resolution you are looking for...even if it isn't "HD".

reply to post by iforget


In the case you cite where light was slowed to a proverbial crawl, it's not photons that were slowed down. You have to understand there are two kinds of velocity: phase velocity, and group velocity. Imagine a punt sitting on the water. It moves with the water, but, as it moves, waves on the surface of the water pass by. The water is moving at one velocity, while the waves in the water are moving at another, faster, velocity. In this case, the slower water velocity is the group velocity (it's the speed at which the water is actually moving), and the faster wave velocity is the phase velocity (the speed at which the wave propagates through the water).
In the case of light, the phase velocity can be anything. It can be much faster than the speed of light, or it can be slowed to a stop. It can even go backwards (if the waves on the water are moving in a direction opposite to that of the water, itself). The group velocity, on the other hand, must always be equal to the speed of light, because it's the speed at which the photons actually move. And, since it's the photons that carry information, the information must also always travel at the speed of light.

So, when you hear of scientists who have slowed light down so far that it's almost stopped, you have to keep in mind, it's really not as spectacular as they're making it sound - they've just slowed the phase velocity. The light, itself, is still moving at the same old speed of light.

reply to post by CLPrime


hm nice thanks for the lesson
I can understand, a little, why the example gave was not suited to my idea but do materials with a refractive index actually slow the photons themselves?

reply to post by iforget


Nope, photons always travel at the speed of light. The slower propagation of light through a material is also a matter of phase velocity. Different media slow the phase velocity of light, they don't slow the photons.

reply to post by CLPrime


very interesting thanks again

Originally posted by CLPrime

Second, you would need a way of imaging the Earth with enough resolution from 2491 light-years away to actually see anything.

This is exactly why you would NOT see the past, but the present.

Once you start using magnification to increase resolution, you are in effect bringing the earth closer to you (visually), so when youu got to whatever magnification was necessry to clearly see the earth, the distance youu traveled away from earth wouldbe a wash.

Originally posted by craig732
Once you start using magnification to increase resolution, you are in effect bringing the earth closer to you (visually), so when youu got to whatever magnification was necessry to clearly see the earth, the distance youu traveled away from earth wouldbe a wash.

That's an interesting hypothesis. However, it doesn't quite work that way.

The magnification we get through the Hubble telescope doesn't physically bring anything closer to us. It only looks that way.

Originally posted by Arbitrageur

That's an interesting hypothesis. However, it doesn't quite work that way.

You're too kind, Arbitrageur.

It doesn't work that way at all. Increasing resolution is a matter of increasing the photon capture, which requires focusing more light, with a larger aperture and/or finer photoreception. The increase in detail, itself, is not properly magnification, so, even if magnification did cause an object to visually get closer, this would not do so. This is a matter of increasing the range and number photons detected.

And, of course, as Arbitrageur has stated, magnification does not reach out and view light from a more contemporary time. So, wrong on two counts.

reply to post by CLPrime


Einstien-ian physics are already starting to be unraveled by scientists. 100 years from now, physicists are going to laugh in disbelief that we ever believed in his theories.

reply to post by craig732


Though, this has nothing to do with "Einsteinian" physics. This is a simple matter of time of flight for light leaving the Earth and the detection of that light at a distant location.

Originally posted by Samuelis
well now we know that neutrons travel FTL

edit on 20-11-2011 by Samuelis because: (no reason given)

They actually don't. Einstein's relativity is still winning.
Source:
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