A friend of mine claims that time dilation is a product of science-fiction, whereas I claim it's based in reality as well. I seem to recall the astronauts experiencing time dilation (i.e. the clocks on-board their shuttle were several minutes behind the clocks here on Earth). Who is correct, and can someone explain it?
Astronauts, airliners up to mach 2 with atomic clocks aboard, and a proton in a particle accelerator thats "aging", had slowed down. It's real. Bonk your friend on the head with "a brief history of time". Hard.
As for explaining it... Well, someone more math minded could get into the guts of it better, but I'll take a crack. Basically, there is no universal objective time. Time, indeed all reality depends on perspective. And speed fucks with that perspective. The phenomenon of an object whizzing by seeming a little bit shorter to a guy standing still, and vice versa, the guy standing still from aboard the whizzing object, that you take for granted as just this funny little thing of life, you magnify that up to near light speed, and time literally slows down. But it ain't gotta be light speed, the atomic clocks proved even airplanes gain little microscopic fractions of seconds.
Yep. Real. You're going to make me explain it, aren't you? Well, here goes... In the late 19th century, physicists made a shocking discovery when they tried to measure the speed of the Earth's motion through the "ether" (which they believed was the substance of the entire universe) using beams of light. Their experiment (too complicated to really go in to--look up Michelson and Morley if interested) presupposed that the velocity of light would add to the speed of what emitted it like the velocities of objects add (that is, you shoot a bullet from an airplane and the bullet's speed is what it would be when fired from a stationary spot PLUS the speed of the airplane). It turned out this was not the case. Their measurement for the speed of light was the same NO MATTER HOW they measured it. This is a contradiction, one which Einstein's insight solved. Einstein theorized that there is NO ABSOLUTE FRAME OF REFERENCE in the universe. That is, no where can you stand and say "this spot is not moving." You can only say "this spot is not moving RELATIVE to some other spot." And because there's no absolute frame of reference, the laws of physics--to be consistent--most hold true for any frame of reference (in other words, Newton's laws, etc. apply no matter whether you're standing on the Earth or in a space capsule). This sounds like a small insight but it has profound consequences. If the laws of physics are the same for me as they are for you--even if we're moving at vastly different relative speeds--then time no longer passes at the same rate for both of us. Let me give you an example to clarify. Suppose you're in a rocket going 100,000 miles per second in space. Suppose I'm on the ground watching you (and, thanks to a super telescope, I can actually see inside your rocket). Now, you point a flashlight toward the front of your rocket and turn on the beam. Nothing unusual or different would occur; the beam comes on and shines a bright spot on the front of the rocket. If you measure speed of the beam, you will get 186,000 miles per second. Just as you would measure the speed of light under any conditions. Here's where it gets weird: if I measure the speed of your flashlight beam from where I'm at, I ALSO get 186,000 miles per second. Despite our vastly different relative speeds, light will appear to have the same speed for both of us. I can't draw you a picture, so you'll have to imagine this next part. Suppose you put your flashlight on the floor of your rocket and bounce its beam off a mirror on the ceiling in order to make a clock. For laughs, let's call the amount of time it takes for the beam to go from the floor up to the ceiling and back ONE SECOND. From YOUR perspective, the light goes STRAIGHT up from the floor to the ceiling and STRAIGHT back down to the floor in order to make one cycle. The beam moves at the speed of light, of course. From MY perspective (because of the movement of your rocket), the light leaves the flashlight on your rocket's floor and moves BOTH forward and upward toward the ceiling (after all, it has to hit the mirror on the ceiling--which is moving at 100,000 miles per second). The light hits the mirror and comes back, moving BOTH forward and downward. We both agree on the speed of the beam--light speed. But we DISAGREE on the length it travelled. For you it was straight up to the ceiling and back, for me it was an angle up to the ceiling and an angle back down (because of the rocket's motion). My beam travelled a longer distance than your beam. Thus, if one cycle of your clock is slower for me than it is for you. It will work the same with any kind of clock. Time on board your fast-moving rocketship is happening slower than it is for me on Earth. This effect is real--and has been measured many, many times. In fact, technologies like GPS (which require very precise timing despite the high relative motion of satellites) depend on it.
Actually, there can exist a sort of 'absolute time', outside of the influence of time dilation. Whatever you choose to classify as time, which might be broken down to say, matter interaction, slows down in individual bodies within the universe attempting to observe it. Picture a game of pool, with each cue ball doing its own jig at a rate influenced by its own behavior (rotation and rate of motion). The absolute time could be measured by the person standing over the table.
Which is just another arbitrary inertial frame. You can do that if you want--it's often very handy to do so--but it's no more intrinsically valid than any other.
You miss the point. If I were to take all states in the universe and try to calculate matter reactions backwards (We'll ignore uncertainty for this) and factor in time dilation stemming from said reactions, I could extrapolate an overall, absolute picture of a universe containing pockets of time passing at different intervals. It is completely valid.
