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Faster than light
Numsgil:
Relativity always made my head hurt.
The reason cestial bodies can move aparty at speeds greater than the speed of light is that the actual fabric of space is expanding. Either celestial body isn't moving greater than light speed in its frame of reference, but compared to each other they look like it.
The end effect is a doplar shift in the light's wavelength that either body recieves. Usually a redshift (I think).
Endy:
I think I read that you have to either do extremly complicated equations or measure the speed from a nonmoving frame of reference, to tell the actual speeds(all of which are less than light).
What exactly would an object going backwards in time look like to us? I heard some talk about antimattter being matter going backwards in time, but that it still can't be used to send a message since we can only observe reactions taking place in a forward direction. My guess is that time travel is possible as long as the law of conservation holds. Since matter/anti-matter are essencially opposites it should balance out. But I'm not exactly planning on volunteering to be turned into explosive anti-matter anytime soon :)
Maybe, like PY says, we're really in a giant computer and all we need to do is to find the savegame file somewhere. Who knows?
Endy :blueblob:
Zelos:
when tis about the special relativity and 2 ships moving at 0,9c and are moving toward each other, there is a formula which tells us they will only see that the other ship is moving whit 0,99C or something like that. nothing can move whit the speed of light relative to anything. and the speed of light is always the same relative to everythingand endy, antimatter is like ordinary matter, but it have the opposite charge, a proton is -1 and a electron (positron) is +1, you get it?
PurpleYouko:
--- Quote ---I think I read that you have to either do extremly complicated equations or measure the speed from a nonmoving frame of reference, to tell the actual speeds(all of which are less than light).
--- End quote ---
Trouble is there is no such thing as a non-moving frame of reference.
I remember a simple example that my college physics proffessor showed us once to demonstrate relativity and why time is the variable rather than light speed. You have to have a pretty good imagination for this.
There is an observer on an asteroid who watches a spaceship fly past at high speed.
On board the spaceship is another observer who carries out an experiment to measure the speed of light. he fires a light beam from one side of the ship to the other, where it hits a mirror and returns to a detector at the source. He knows the distance travelled and he measures the time taken so he can easily calculate the velocity. Distance = twice the width of the ship. Time = t. Go figure.
The observer on the asteroid is able to watch the beam of light that traverses the spaceship and makes his own measurements of it. To him the light beam doesn't simply cross the ship and back in a straight line, It travels diagonally as the spaceship is moving. Let's say the ship is moving at the correct speed for the light beam to be moving at a 45 degree angle to the perpendicular.
From the asteroid observer's frame of reference, the light beam travels a much greater distance than it does for the observer on the spaceship. he measures that distance as 2 * the square root of (double) the square of the width of the spaceship using simple trigonometry.
He calculates the speed of light from his time and distance measurements.
According to Einstein, both observers will measure the speed of light to be exactly the same.
We know that the light beam must actually be moving in the way that the observer on the asteroid sees it since the ship is in motion. It is logical that the light beam must be moving with the direction of the spaceship's travel and not just side to side since it takes a finite time to complete its trip.
Therefore, in order for the observer on the spaceship to measure the speed of light to be the same universal constant, his time must be moving slower than that of the observer on the asteroid. (relatively)
Everybody follow this still?
I will leave it at this point before carrying on. More later.
:D PY :D
shvarz:
Makes perfect sense to me. I guess the question I have here is how these two guys know which one is moving and which one is sitting still? It might as well be that the ship is stationary and the asteroid is passing by :)
Also, on the practical side of things: these two dudes seem to observe and measure the speed of light without any special equipment. In real life they'd be somewhat distanced from the beam of light in question and will use some physical phenomena to a) measure the distance the light travels and B) measure the time. These measurements would introduce another level of calculations and make the problem really complicated! I'm glad I'm not a physicist to figure all this stuff out :)
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