2 Questions: Are these possible?

S

satchguitar

Temporal Novice
Hi, I had 2 questions that I've been trying to find details on the web but haven't had much luck.

1. I heard a few years ago that some scientists sent a radio signal (or whatever type of signal it was) through a tube filled with xeon gas (or some kind of gas) into a chamber and out through another tube. They managed to send it faster than the speed of light, and in fact, the signal actually went through the exit tube before it even entered! Does anybody have any details on this or where I can find it? I'd like to read up more about it.

2. My Astronomy professor told the class that if you looked through a really powerful telescope really far out into space, theoretically, you would be able to see the Earth at a certain point in the past because of the curvature of space/time. I know that the further out you look out into space you're actually looking back in time. Would it be possible to see the Earth at a certain point in time?

Let me know what you think. Thanks!

Jon.

I love brain candy!
 
satchguitar,

Keep in mind that the speed of light "c" is given in a vaccum. The xenon gas is obviously not a vaccum. It has a refractory index (as do all materials) and light travels at less than "c" through those materials.

I vaguely remember the experiment that you refer to. If I can find it on ArXiv or LANL I'll post a reference. But the results were not a surprise to the experimenters or anyone else.

As to your second question, yes. Gravitational lensing (if it is really extreme) for instance would result in the same situation. Light is reflected from the Earth today, rtavels past some huge gravitational source, bends through 180 degrees and ends up coming back to Earth.

On a much smaller time scale you do this every morning. You look in a mirror and see yourself as you were very slightly in the past.

Your professor is correct about the "in theory" situation. But the real universe appears to be virtually flat. The curvature is almost non-existent. So much so that it has not been detected. It would take "forever" for the image to come back to the starting point based solely on the universal curvature of space-time. And when it did it would be at a uniform temperature of about 3 degrees Kelvin - the same as the cosmic background microwave radiation that you see and hear as "snow" on a TV without an antenna. The image would be lost in the clutter.
 
satchguitar,

Just a quick follow-up:

In theory the light could be reflected back to the source due to the curvature of space-time, as I refered to above. But that assumes that the universe is closed. Meaning that there was a Big Bang and the universal curvature will end up with a period of expansion followed by a period of contraction to a Big Crunch.

But the current theories indicate that the universe is open - not closed. The curvature is positive and there will be no future contraction. The universe will continue to expand forever and there will be no Big Crunch.

Times change, evidence is gathered and the Big Crunch vs. Open Universe question has not been answered yet.
 
In theory, when the universe has finished expanding from the big bang the big crunch will happen. This is in part due to a black hole at the origin (the point at the exact center of the big bang) and in part due to the black hole pulling in on the expanding universe, thus slowing it down and decreasing the time until the crunch itself happens.

If I make any sense there.
 
Hi Doc,

This is in part due to a black hole at the origin (the point at the exact center of the big bang) and in part due to the black hole pulling in on the expanding universe, thus slowing it down and decreasing the time until the crunch itself happens.
Click to expand...
Only problem with this is that recent data has shown that the universe is not slowing down, and is not even expanding at a constant rate. It is actually accelerating. This is just some of the data that supports the possibility that Dark Energy is actually an anti-gravitational force in between the galaxies that is causing this acceleration.

RMT
 
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