Why does time slow down as one approaches the speed of light?

One thought experiment that shows that time does in fact slow down is to imagine two inertial frames of reference- call them spaceships if you want- moving relative to each other. Say that each ship has a clock on board that has a beam of light bouncing back and forth between mirrors. Now, when you look at your own clock, you are not moving relative to it, and you simply see the beam following a straight path perpendicular to the mirrors. But when you look at the other person’s clock, between bounces the clock moves forward a little, and so the light is following a diagonal path that is longer than the path taken by the light in your own clock, according to the Pythagorean theorem. Light always travels at the same velocity no matter the frame of reference, so the light, from your perspective, must take longer between bounces. But the other person, who is not moving relative to their own clock, sees the light as traveling on a perpendicular path (identical to that in your own clock as seen by you) and therefore the time they observe between bounces is shorter than that you observe. As both observers are in inertial frames of reference, and all motion is relative, both observations are equally valid, and the only way to relieve the paradox is to say that time passes slower for the other spacecraft than for you. But of course the same can be said for them as well. However, when one ship decelerates their clock slows down from their perspective, and speeds up from the perspective of the observer, meaning that the clock on the ship that has kept a steady pace will have registered less time than the other when they meet. I think. Although that seems to contradict the twin paradox. Hmm…I’ll have to think on it a bit more.

In the twin parodox why does my twin age and not me. Who says that she isn’t standing still while the universe moves around her? I don’t really understand the mechanism behind this.

I’m not sure, so I cheated and went on the internet, and found that this site explains it well. Be sure to surf around the links.

I’ll go ahead and ‘fess up. I’m the friend that’s doing the arguing. Of course I’m not arguing just for the sake of argument (of course I would never do that. . . ). I simply cannot understand how time can be altered. I’m trying to see the flaws in my ideas of time. I will look at that site though and see if I can make sense of it.

@mrswho It has to do with the fact that one twin experiences acceleration to get to the speed of light and one does not.

In terms of the mechanism, and why it happens, the easiest way to understand it is a bouncing light. You have a light that bounces back and forth between two mirrors. From the perspective of the twin on the space ship, the light is bouncing normally. From the stationary observer, the light has to bounce a longer distance between the mirors because his twin is moving. Since lightspeed doesn’t change, and it has to move a longer distance, it takes longer. Therefore from the observer’s point of view, the twin’s clock moves slower.

I prefer to look at it mathematically from the Lorentz Contractions, but it’s hard to write out in a post.

If you travel through space, close to the speed of light doesn’t that just mean you will get to the destination faster and the the time alter is just a illusion. Because the earth will always have it’s set speed at which it it goes and all other planets have a different speed depending on how long it takes to go around the sun. Why would it matter how fast you travel?
Speed 1 (fastest) Earth O————————————————————> O point B (took 3 earth years)
Speed 2 (slow) Earth O————————————————————> O point B (took 300 years)

Wouldn’t the fastest speed just take a shorter amount of time to travel, and the reason of time’s change in speed is because of the distance from the sun is further away. The further away from the sun the longer the year is.

I know it’s been proven, that’s why I feel REALLY ignorant, but no one has really explained how the effect works.

If you travel (assuming you can right now) close to the speed of light for 10 years earth time, why and how would earth be further in the future. Wouldn’t you just be further away from earth?

The most direct way of thinking about it, in my opinion, is to remember that time is a dimension, just like space. We usually think of space as having three dimensions, and any motion can be broken up into its components, motion in the x, y, and z directions. Imagine that an object always has the same speed, but can travel in any direction. Thus, the faster it moves along, say, the z-axis, the slower it moves along the x-axis, because more of the available speed is ‘used up’ in traveling in the z direction. Now add the dimension of time; we are dealing not with space, but with spacetime. No object can travel faster than the speed of light, so this speed acts as the constant speed in the above example. Naturally, the more of this speed is used up in the three spacial dimensions, the less of it remains for the time dimension; the object does not travel as far through time. In a very real sense, time has slowed down.

This explanation is very imprecise and is riddled with flaws, but it should give you a decent understanding of the basic ideas at play. These ideas, of course, have nothing to do with the basic distance = rate*time formula that applies to basically everything in our daily lives, and which you tried to use above, because time is really a part of distance, it just isn’t a significant part at the speed we usually experience.