How speed changes time?

You have encountered the paradox of time travel. According to Einstein, there is only relativistic time. The only situation when a clock will keep accurate is when it is adjacent to an identical clock in the same time and space. If one clock moves, it will be affected by the relative change in velocity. As I approach the speed of light, a clock removed from me will appear to be keeping time in a faster manner than MY clock. And my clock will appear to be going slower than THEIR clock. When I return, the two clocks will display a different time proportional to the change in velocity between the two clocks over the time separated. No one actually KNOWS this to BE true, but indications are that time changes as you increase in speed. This was actually proved with two cesium atomic clocks. One in a fast plane traveling east, and one traveling west. Two Identical clocks which had gone for years in the same place keeping exact pace with each each other. After circumnavigeting the globe, the clocks WERE slightly different, out of sync. The only variable was the speed the clocks traveled relative to each other. One or the other or both of the clocks changed to get them out of sync, indicating that time really DOES change based on speed. Compared to clocks left behind in Boulder, CO where the National Bureau of Standard is located who ran the test, the clocks all in sync, one clock gained time and the other lost time compared to the ones left behind. The point to remember is that all of the clocks before the test were in sync for YEARS, and then after only a few days of travel east and west, came back with differing times and for years since, have maintained the exact same difference between the clocks that moved and the clocks which remained behind with no movement. The reason why east and west is significant probably eludes you. The rotation of the Earth is about 1000 miles per hour, so it adds to the eastward velocity and subtracts from the westward velocity as compared to the stationary clocks in Boulder.

Sir Daniel Fortesque is right - the key here is that the two situations are not truly equivalent. If taking only the speed into account both you in the rocket and the people (let's say your twin) on Earth are fully equivalent. Both you and your twin think it is the other persons clock that is slowing down. Both of you think your own clock is keeping perfect time.

The thing that brakes the symmetry is the fact that only the rocket is going through several inertial frames. That is exactly enough to ensure that, when you return to earth after having travelled near the speed of light for a bit (note, you do not even need to be heading "away" as such, it is good enough to circle the planet) you will both agree that it was your clock that actually slowed down. You have "travelled into the future".

Contrary to what was stated before this effect has actually been proven through careful time measurements.

Not my source but it seems a good overview http://en.wikipedia.org/wiki/Twin_paradox

Yes, you will also notice their clocks moving slower. You are right, the Earth is traveling away from you at the same rate you are traveling away from it. So Earthings will see your clock run slower, and you will see clocks on Earth run slower.

The twin paradox will age one twin because that one has to accelerate in the rocket and decelerate and that takes them out of an inertial reference frame.

Dean is way off base. Time on board the rocket actually slows down relative to an outside observer who is fixed relative to the ship. If we could see it from Earth, we'd see your $5,000 Rolex lose time and the faster you went in the rocket, the more it would lose time relative to our clocks on Earth.

This not only affects your Rolex, it also affects your heartbeat rate, which also slows down. In fact, your entire basal metabolism will slow down; so you will not age as fast as that person on Earth.

On the other hand, if that outside observer were to climb into another rocket and come up along side yours, so your relative velocity re his ship is zero, then you would see his Rolex and your Timex would be in sync. That results, because you are at rest relative to him and he is at rest relative to you in this case. So between the two of you, time marches on as normal rest time.

All this time slowing stuff is called time dilation. It is a major result of the general and special theories of relativity. Most of the time, we don't experience time dilation. It's there, but it's so small we just don't see it.

But significant time dilation happens when relative velocities are extreme, like with the rocket. This is described in the special theory.

It also happens when that Rolex is subjected to extreme gravitational force, like in a black hole. This is the effect of the general theory, which describes spacetime and how it bends under extreme acceleration, like from gravity.

as you go faster time moves slower;

your clock will appear to tick at it's normal pace to you. and similarly, the clocks on the earth will appear to tick normally to earthlings.

but as far as i know, to earthlings your clock is ticking slower, ie you are traveling back into time WRT them.therefore their clocks will appear to tick a slightly faster to you.

and yes, this is similar to the famous "twin paradox" theory.

speed doesnt alter time...all it does is give the appearance that time is slowing down. No matter how fast you go, the clock will keep ticking at the normal speed. (you get to a location ten minutes early because you were driving 70mph instead of 55mph, did time slow down?)