# Special relativity question

#### laocmo

This confuses me. According to the examples often used in introductory special relativity theory books, if a spaceship leaves the earth and travels towards a far distant galaxy at near the speed of light. Then turns around and returns to Earth, perhaps 10 years will have passed for the traveler and perhaps 1000 years for the earthlings. Thus as reckoned in the traveler's reality things on Earth would have had to speed up so that 10 years worth of traveler time would accomplish 1000 years or earth-time efforts.

Every Earth process from building a skyscraper to finishing a chemical reaction would have had to speed up by a tremendous amount to fit the traveler's reality. Where does all the energy come from to increase the speed, kinetic energy, momentum, etc. of the stationary earthlings? According to theory the earthlings would notice nothing out of the ordinary? Even though they are moving around at very large velocities to get all that 1000 years worth of activity finished in the traveler's 10 years of time.

#### HallsofIvy

From the reference frame of the "skyscraper", etc., nothing has changed. There is no "speeding up" and no energy is needed. The person who is moving, relative to the earth, observes a change in time, relative to his frame of reference.

1 person

#### laocmo

I realize that the traveler time has slowed up relative to the earth time, yet the traveler has every right to his own reality. And in it, the earth's processes have all apparently sped up. So to the traveler, the earth has expended an awful lot of energy to accomplish in his 10 years, 1000 years worth of efforts. To the traveler everything on earth must have happened extremely fast. To the traveler that would require a lot of energy.

#### Woody

One could also look at it the other way,
the traveller is expending energy to slow down his time relative to Earth.
However, this is not correct either.

Perhaps a better analogy is that the traveller and the stay-at-homes are viewing things from different perspectives.

They are viewing space-time from different "angles",
Ones space becomes the others time, and visa-versa.

1 person

#### laocmo

If nothing else relativity proves there is no universal reality. As the traveler my 10 years are real. To the stay-at-homes their 1000 years are real. Does anyone know of a good book on how relativity has changed the way philosophers handle the post relativity world view? Is there a good philosopher author who thoroughly understands relativity?

#### topsquark

Forum Staff
If nothing else relativity proves there is no universal reality. As the traveler my 10 years are real. To the stay-at-homes their 1000 years are real. Does anyone know of a good book on how relativity has changed the way philosophers handle the post relativity world view? Is there a good philosopher author who thoroughly understands relativity?
I'm not sure about any Philosophical trend but probably the best author you are going to find is Sir Arthur Eddington. He did a lot to bring Relativity to the world at large.

-Dan