Known space = light speed, dark matter = dark speed?

Question

If a spaceship travels in light speed to the nearest galaxy upon his arrival Earth will be a few million years older. Action and reaction exists apparently everywhere and in everything. Is it safe to say that the ship in order to return to its point of origin will have to travel backwards in space and time. Will the understanding of dark matter and energy will provide us with an answer?
And what about the paradox? As the spaceship travel in light speed and the earth gets older and more technologically advanced wouldn't the dissendents of the travellers catch them on route or meet them at the finish line?

Answer 1

I think you're mixing up a lot of stuff here and you're really confusing yourself (and me and that's not easy to do).

The first paragraph of yours makes no sense. A space ship travels at light speed away from Earth to a distant galaxy. From the point of view of the Earthling, time halts on the the spaceship... its as if all the clocks have stopped. From the point of view of the spaceship it looks like time halts on Earth -all terrestial clocks have stopped.

Now when the spaceship gets to the distant galaxy (it takes a million years let's say) and looks back on Earth, it will see Earth exactly as it left it (remember -from the point of view of the spaceship -Earth's time stands still). The same is true if Earthlings watched the spaceship.

The paradox this creates is solved however once the spaceship at the distant galaxy tries to communicate with Earth. Say at the distant Galaxy, the ship sends a fax back to Earth. The fax traveling at the speed of light, takes 1 million years to get to Earth (2 million years would have passed since the original spaceship left).

You have to remember that NOTHING travels faster than light -not even information (which is wound tightly with observation).

Action and Reaction have nothing to do with relativity so no -its not safe to say that for the ship to return to its original origin it would need to go back in time. For the sake of this discussion lets say there's an arrow of time and it only points in one direction.

I think you're refering to anti-matter when you say dark matter. Dark matter is mass in the universe that we have measured by looking at gravity but can account for in our observations. Anti-Matter is a whole nother world onto itself - the origins of which I am woefully ignorant of but I understand that there is a lot of theory around using it as power source (mixing matter and anti-matter)

Lastly- the scenario in your last paragraph is not a paradox - it could happen and without any unusual things happening. Lets say spaceship A leaves Earth to a distant galaxy 1 million light years away at the speed of light (no acceleration for the sake of argument). 500,000 years pass and Earthlings discover a worm hole so it would only take half a million years to make the trip. They send Spaceship B to the galaxy to greet Spaceship A when it arrives. Finally at 1 million years both Spaceship A and B arrive at the galaxy. To both spaceships at this distant galaxy, Earth looks like it did when A left 1 million years ago. The people on spaceship B think they traveled back in time but they didn't... it only looks like that. If the space ships send a email back to Earth the usual way through a radio it would take 1 million years to reach Earth (the Earthlings would get the message 2 million years after the Spaceship A left -that's forward in time - not back). Even if they sent it through the worm hole the Earthlings wouldn't read it until 1.5 million years after Spaceship A leaves and still half a million years after A and B send there message.

Einstein's relativity doesn't allow for the kind of time travel that Hollywood likes to show. You can go back in time... but only as an observer and the result is only relative (hence the name of the theory).

My favorite answer to the whole "can we travel back in time" question is from Steven Hawking.

"If time travel were possible, we'd be inundated by time travellers form the future."

Answer 2

First let me correct a bit of physics. You can only travel one way in space time, thats forward. If you could travel at light speed, then go out to a planet and came back you would be a long way into the future, no traveling back in time.

In response to Orangle, the trip time for the person on the ship(lets say you were going to the closest star, 4 light years away) would be about 4 years. But to the outside observer it would take much much longer(don't want to do the calculations.)

As for your paradox, you probably would get there only to realize that the human race is extinct. But on the up side they had already been there and left you a nice new space ship. :)

Answer 3

well accually, according to einstiens theory, if you travel at light speed, you travel at the speed of time, and there for, if you keep traveling at light speed, you will reach the other galaxy in literally no time at all.
It is almost like you were to freeze time, travel to your place, and defrost it again
so basically, all the time it took you was, the launch from earth to space, and the acceleration time it took you to reach the speed of light

Answer 4

Ya know what? Why don't you turn off the star trek reruns for, oh lets say one day, and go outside, sit on the grass, enjoy the sun while treating yourself to a triple scoop of your favorite ice cream.

Answer 5

dark matter merely refers to matter that we cannot see in the universe. It is not some form of exotic matter that is subject to new laws of phsyics such as dark energy