Why when I travel at near light speed and return to Earth has more time passed there than for me?

Yes.
In a documentary hosted by Brian Cox, I think, it was said that a total amount of energy is available to an object travelling through space and time. The more energy you spend on an object moving through spatial dimensions, by accelerating it, the less energy is available for movement through the dimension of time, making the passage of time slower for the travelling object.

I think I get that Ragingloli. Thank you.

Think of it also this way. Let’s say you have a light beam bouncing between two mirrors, up and down. If you’re on Earth and you have the light beam you see it moving up and down. You take it in the spaceship and you still see it move up and down, the same as you’re on Earth.

Now, pretend that you’re on Earth and you can somehow watch the light beam bounce up and down on the spaceship while it’s moving. Instead of seeing it move up and down, you’ll see it move in a zigzag pattern as the spaceship moves forward.

So for the observer, the light is moving farther between each bounce than it is if you’re on the spaceship looking at the same thing. Since light moves at a constant speed regardless, and it moves farther for the observer, the observer sees time move slower for the person in the spaceship. But in the spaceship, since the light is bouncing normally, time seems to move normally for you.

The sticking point is as follows: Hasn’t the Earth, at least while I was heading away from that planet, been travelling at near light speed from my perspective? That’s true, which is why the Twin Paradox is a paradox.

What breaks the symmetry, to make the astronaut different from his twin, is that he turns around to return to Earth. This requires acceleration, while the stay-at-home twin remains in an inertial frame the whole time. According to general relativity the traveling twin arrives younger, as has been abundantly confirmed by experiment.

Who’s younger before the astronaut turns around, while they’re both traveling in inertial frames? Each seems to be aging slower than the other! But there’s no paradox because they’re not together in space and time for comparison.

Thank you all. I think I may get this.

So Gasman, I can see the experiment Rarebear describes being performed on Earth in my rearview mirror, and they seem to be slowing down. But when I turn around, that same experiment, and earth local time, would appear to accelerate rapidly? As Ragingloli put it, I need to think of two factors, Space and Time energy which sum to a constant.

I think it was this documentary: http://www.youtube.com/watch?v=ULlR_pkHjUQ&playnext=1&list=PL725BA485D19A9ADB
It was Brian Greene after all, not Cox.

Well, the one twin has to accelerate to light speed, which breaks symmetry, then decelerate to come back.

You’re referring to the twin paradox. At first glance, it seems that your situation and Earth’s are identical: by Earth’s frame of reference, you’ve been moving near the speed of light; by your frame of reference, Earth has been. Who chooses which frame of reference is the “real” one? As @RocketGuy pointed out, however, the situations are not identical. You have accelerated and decelerated, while Earth has remained at a constant velocity. I’m not sure if it is fully understood, yet, why exactly this matters.

@Imadethisupwithnoforethought Yes, @Rarebear describes the classic “light clock” imagined for relativistic scenarios, “ticking” as light bounces between parallel mirrors a fixed distance apart.

@RocketGuy Yes, but symmetry isn’t broken until one of them turns around. Achieving near-light speed in itself does not raise a paradox. Imagine that the astronaut twin has already accelerated to near-light speed from outside the solar system, then goes whizzing by on a trajectory that glances the Earth. Time zero occurs when the astronaut passes overhead. At this particular point in space-time the clocks are reset to zero and both twins are in inertial frames. Each sees the other aging more slowly as they fly apart.

It’s the later acceleration (inevitably required to return the traveling twin to Earth) that accounts for one twin showing up younger. Their paths through spacetime are now very different.

@gasman Exactly. Brian Greene explains this beautifully in The Elegant Universe.

I think the sticking point might be this: it’s not the speed that causes the fun relativity time warp stuff, it’s the acceleration.

When you accelerate, time goes slower for you.

Your question is directly related to Einstein’s theory of relativity E=mc2. As an object approaches the speed of light, it’s mass changes and so does the frame of time relative to an observer perceiving the object’s motion from a great distance. The theory supports the hypothetical factor that time is not always a constant relatively speaking. It would be a similar analogy to ask the question, “What’s north of the north pole?” If you were trying to determine a point in space, the word “north” would do you no good. N. S. E. and West are only relative to longitude and latitude on the surface of the earth. Looking up Einstein’s theory of relativity and also the Universal Field Theory might explain the answer to your question more clearly and in better detail.

I don’t think it’s true that the accelerating object’s mass changes…

Very true….It’s mass elongates. I’ll look up a reference for you.

As the object approaches the speed of light, the relativistic mass grows infinitely, because the kinetic energy grows infinitely and this energy is associated with mass.

I pasted the above sentence from this link:
Mass–energy equivalence – Wikipedia, the free encyclopedia

Oh. That makes sense.

I think.

I don’t get it all either because I’m not a math wizard; but the basic concept is pretty interesting if you can find the books that explain it in layman’s terms.

I’m moving over to psychological and bi-polar disorders. Take care and “Happy Research & Reading”!

Shariw and Quingu, I get the mass increase thing, but thank you both for trying to help. I imagine speed spilling into a hypothetical ‘Mass’ dimension when I need to think about it.

Everyone else, thank you for the book recommendation. I am just finishing the Hidden Reality; sounds like I should have started with the Elegant Universe by that author. Thanks again everyone.

@Qingu “it’s not the speed that causes the fun relativity time warp stuff, it’s the acceleration.” Well yes and no. In special relativity—everybody in an inertial frame with no acceleration or gravitation—a high-speed object always undergoes a slowing of time, a shortening of length, and in increase in mass as seen by the stationary observer. Acceleration not required.

My point about the importance of acceleration in the twin paradox is that the scenario is more complicated than with two observers simply traveling at close to the speed of light with respect to one another.

@gasman “acceleration is not required”. But in order for the high speed object to get high speed, doesn’t need to undergo acceleration?

@Rarebear: well, yes. From a standing start on Earth it takes a lot of energy just to get single particles up to relativistic speeds, especially with ever-increasing inertia causing asymptotic approach. That’s why LHC is so expensive.

Mathematically there’s nothing special about an object going 0.99999c as opposed to, say, walking speed. The theory treats them similarly with one set of equations. Only the magnitude of the effect is remarkable.

See the delightful Mr. Tompkins series by eminent physicist George Gamov (d.1968) where the speed of light is so low that relativistic effects pervade ordinary life. The wheels of moving bicycles look taller than they are wide, etc.

@gasman I hadn’t heard about the Mr. Tompkins series. But at first glance it reminds me just a little bit of Flatland.

@Rarebear Yeah, kind of in the same vein—fantastic adventures to illustrate science—but not so Victorian! . Btw the author’s last name was Gamow not Gamov. Wikipedia says, “Gamow’s lifetime interest in playing pranks, punning, and doggerel verse come across in some of his popular writings, notably his Mr. Tompkins… series of books (1939–1967)...”

Is it too late to ask a follow-up?

What if the universe was in some manner round? Would this experiment, performed on a Möbius strip, yield a different result?

@Imadethisupwithnoforethought The physics of relativity should be the same regardless if the universe is closed or open.

In the Elegant Universe, it suggests that the theory of relativity works best in reference to large objects with enough mass to be affected by gravity. It states that quantom mechanics is best applied to smaller atomic and sub-atomic particles. The two theories are individually infallible, however, breakdown when both are used together in a single equation. The Universal Field Theory which makes use of both without contradictions is where Einstein left off upon his death. Stephen Hawking, one of the world’s most intelligent scientific geniuses of our time has come very close to solving the problems of the 2 seperate therories as they relate to each other in a unified way. Hopefully he will be able to unify the field theory where Einstein left off before the depilitating disease that grips his physical body wins over his life and puts an end to the one incredible mind that has come the closest to solving the puzzle. I pray for his success as well as the advancement of the scientific community that would prosper from such an enormous break-through.

@shariw I read Brian Greene’s Elegant Universe back in the 90s. It sounds like you learned some good lessons—I agree with all you said. Einstein died in 1955 while seeking in vain to unify gravitation and quantum mechanics. The strong and weak nuclear interactions were not worked out yet. Black holes and the big bang were mere speculations still lacking observational confirmation. We’ve come a long way. We now know that electromagnetic and weak forces are equivalent at very high energies, and that the strong force shares some symmetries as well. Among the 4 forces, gravitation is the odd man out. There is no quantum theory of gravity.

Hawking showed that black holes, despite their intense gravitation, emit radiation in accordance with quantum mechanics & eventually evaporate.

Another world-class genius theoretical physicist is Edward Witten, who helped develop string theory, which might be the next step in unification. Nobody knows because we can’t do experiments in labs on Earth at the so-called Planck scale.