Ok, just say for a moment you are traveling at c or 99.999999 c. Would you die? If the electrical pulses in your body cannot complete its cycle, how would one live? Hmm, actually the atoms that make up your body would cease rotating, or go the route of least resistance…backwards. Wouldn’t you and the ship you are traveling just poof into a cloudish thing of subatomic particles being forced away from the momentum?
No, you would not die (you should write 99.999999c as 99.999999% c or [more usually] 0.99999999c).
If you were going that fast you would feel no differently than you do right now. In point of fact you could consider yourself at rest and assume the things travelling towards you are moving at 0.99999999c. There is no way you’d be able to determine which is correct (whether you are moving or they are moving).
Going ‘poof into a cloudish thing of subatomic particles’ would only happen if you drastically changed your momentum in a short period of time. You can see the same effect at much slower speeds by driving your car into a wall at 50mph or so. You may not disintegrate into a cloud of subatomic particles in that case but as far as your life goes the effect will be substantially the same (i.e. you’re dead).
But if you are going that close to the speed of light, when the electrons spin around the nucleus, wouldn’t they be breaking the speed limit and be achieving +c? If one achieves light speed through some miracle, wouldn’t all forward motion cease, since everything is going as fast as it can? It just seems that if it cannot go forward, the energy in the atoms(still being present)would cause it to go backward.
Not so. Einstein sez: if you add two velocities which are less than c, the sum is always less than c. Say you’re travelling at 0.8c away from the Earth, and you shoot a rocket forward from yourself at 0.6c. You (and Galileo) might think that this rocket was moving at 1.4c away from the Earth, but that’s not the case. It’s actually moving at more like 0.95c with respect to the Earth. Pretty convenient, don’t you think?
Hmm, strange, that one twists my brain a bit. So if you are in a spaceship traveling at .5c, and you turn on your headlights, to an outside observer it appears as if the light from the headlights is traveling at 1.5c, but is only traveling at c away from the spaceship?
So basically light can travel at any speed, as long as it does not break the speed limit from the perspective of the person going the fastest?
As Achernar pointed out this would not be the case. All sorts of tricks start getting played on you as you approach the speed of light. Most famous among these is that time slows down. This time dilation is not apparent to the person actually moving near c but would be apparent to a ‘motionless’ observer watching the light speed traveller.
As a result, like Achernar said, when you add the two velocities together you ALWAYS get a speed less than c (remember, velocity is distance/time…change the time component and you get a different velocity).
No, I see in your post you put two velocities under c. hmm
I think I actually understand it.
If a ship is traveling at .8c and shoots a probe out of it, traveling at .5 c, space time would warp around it, slowing the relative velocity in a local area, sort of like water slows down light. From an outside observer, such a warping is not apparent though. Is that right?
I meant to answer this in my previous post but I forgot.
If through some miracle you achieve light speed then yes, all forward motion would cease. In my previous post I mentioned that time slows down as you approach c. If you actually hit light speed time stops. Again, since speed is DISTANCE/TIME if TIME is zero (or null?..dunno) your motion has essentially stopped. You are frozen in time till the end of the universe.
If you go faster than c (again, through some miracle) then you do go backwards…in time.
There are all sorts of issues with reaching light speed however that keep it an unreachable goal so it’s not likely you’ll be seeing anyone doing it anytime soon.
If you turn on your headlights while driving at the speed of light, what happens?
If I fire a gun while near light speed, will the bullet EXCEED light speed?
Im open to reconsideration but I could have sworn that every physicist’s book and occupation I may have spelled incorrectly has made a reference to a massive change of shape/mass when approaching the speed of light. Stretching into a noodle didnt simply have to deal with entering event horizons of black holes. Im offering this up not as an answer with any authority but as a bump and an excuse to be politely flamed.
If you were travelling at/near the speed of light and you observed someone who wasn’t, and they observed you…
They would move so fast that you would see their whole life pass by in an instant…(your observation)
To them, you would be in super-super-super slow motion…
(Did I get this wrong? Isn’t this perception problem the same when one person is in the gravity approaching that of a black hole, and the other is in earthly gravity? The person near the black hole is in slo-mo to the earth bound observer, while the earth bound observer is a blink of time to the person near the black hole?..travelling near c does the same…no?)
No. If you are travelling at 0.5c and you turn on your headlights, to an outside observer, it appears that the light from the headlights is travelling at c. If you measure how fast the light is travelling relative to you, you will also measure its speed as c.
Basically light can only travel at c. And every observer measures light travelling at c relative to them.
If you add two velocities both less than c, the result is always less than c. If you add two velocities and one of the velocities equals c, then the sum is c.
The only absolute velocity is c. All other velocities are relative.
There is a contraction in the direction of motion. If you are moving past me, I would see you contracted in the direction of your motion. You would not notice your contraction, but I would be contracted as observed by you.
**Philster **
Since all veolcities less than c (including rest) are relative, the situation is symmetric. If I am travelling near light speed past you, then you are travelling near light speed past me. Your clocks and your motion appear to be slowed to me. My clocks appear to run slow to you.
If you are going to bring in gravity, we will need to go from Special Relativity to General Relativity. When you have a gravitational field or acceleration, the situation changes and you lose the symmetry.
Got it. (maybe)
But what about the example that if you are travelling in a ship near the speed of light for one year and returned home, you would be one year older, and your friends would be dead? The speed slowed you down, so to speak.
I’m still missing something because the example above was beaten into my head.
[QUOTE]
*Originally posted by Philster *
**
I think what you are asking here is commonly referred to as the “Twins Paradox”.
Relativity says that if I am travelling towards earth at nearly light speed it is just as reasonable for me to say I am standing still and the earth is travelling towards me at light speed.
“Gotcha,” you say. “If I travel away from earth at light speed for some time then turn around and come back it is clear that I was the one moving since everyone on earth has aged more than me.”
Turns out this isn’t the case. I’m a bit unclear on this one because it’s kinda subtle so anyone who knows better please help me out. I think the quick answer is that in your spaceship you fly away for awhile, stop (or decelerate) and then accelerate back towards the earth. It’s your acceleration that breaks the thing up and makes it clear that you are the one moving without violating any rules of Relativity.
Do a search on this board or with any internet search engine on the Twins Paradox (even though it’s not really a paradox) and you’ll find tons of hits. I know I’ve asked about it here on the SDMB several times myself.
From the photon’s perspective, does it exist? The time, as preceived by it between emission and absorption would be zero, wouldn’t it?
Well first of all a photon can’t have a frame of reference or perspective. Light must travel at c wrt to all frames and light can’t travel at c wrt light.
But, ignoring this then, yes, time comes to a stop for a photon, distance in the direction of travel shrinks to zero, and it cannot be emitted unless it is absorbed. (And in fact the latter is always true.)
The twin paradox can be explained using SR but it is easier to understand using GR. When the traveling twin turns around it is as if the entire universe reversed direction and he is subject to a huge gravitational field. And gravitational fields cause time to run slow.