Relativistic interstellar travel

[ar81]

If time passes faster as you are away from gravity sources, it means that interstellar travelers would age faster, making the trip longer than it should be with our intuitive understanding.

Right?

What could be the implications of that for space travellers?

 

[Hielor]

If time passes faster as you are away from gravity sources, it means that interstellar travelers would age faster, making the trip longer than it should be with our intuitive understanding.

Right?

What could be the implications of that for space travellers?

I believe that gravity's effect on the space traveller would be far outweighed by acceleration's effect on the space traveller, which has the opposite effect (of making the traveller age slower as compared to his "twin" on earth).

This is assuming, of course, travel at relativistically interesting speeds.

 

[ijuin]

There is also the matter that the slowing of time caused by the gravitation of the Earth and the Sun at Earth's orbital distance amounts to something like a few parts per million as compared with interstellar space in this part of the galaxy. You generally have to get too close to a star or stellar remnant (white dwarf, neutron star, black hole, etc.) for human safety before gravitational time dilation becomes worse than having to reset your watch every so often.

 

[RisingFury]

The time distortion due to Earth's and Sun's gravity is insanely small. It would be FAR exceeded by the slowing of time to just getting to massive velocities...

 

[the.punk]

Yes. I think the effect would be very small.
The effect gets bigger when you are near a black hole.

 

[ar81]

It means you may slow your aging if you slingshot around a black hole.
Right?

I do not get it. If there are no gravity sources, and two ships travel near speed of light, each observer would see the other aging slower. So in net terms both should age the same.

Else we enter a paradox, since both will age more than the other.
Right?
I never understood relativistic travel physics. It was porly taught at university and they did not cover it too much.

The only case where I see nice gap in aging is with gravity sources.

 

[the.punk]

I do not get it. If there are no gravity sources, and two ships travel near speed of light, each observer would see the other aging slower. So in net terms both should age the same.

Else we enter a paradox, since both will age more than the other.
Right?
I never understood relativistic travel physics. It was porly taught at university and they did not cover it too much.

The only case where I see nice gap in aging is with gravity sources.

You're right in that. It seems like a paradox. But it isn't.
A better example is when a ship accelerates from earth to near light speed. From the earth it looks like the astronaut ages slower and from the astronaut it looks like the earth ages slower.
This is when you are not accelerated or deccelerated. Then you are a inertial system. But as you deccelerate you aren't a inertial system.
And as you arrive the people on earth are older as you.
This is known as the twin paradox:
http://en.wikipedia.org/wiki/Twin_paradox

 

[Kozak]

EDIT: did not refreshed page.

 

[ar81]

In physics, the twin paradox is a thought experiment in special relativity, in which a twin who makes a journey into space in a high-speed rocket will return home to find he has aged less than his identical twin who stayed on Earth. This result appears puzzling on this basis: the laws of physics should exhibit symmetry. Each twin sees the other twin as traveling; so each should see the other aging more slowly. How can an absolute effect (one twin really does age less) result from a relative motion? Hence it is called a "paradox". In fact, there is no contradiction and the thought experiment can be explained within the standard framework of special relativity. The effect has been verified experimentally using precise measurements of clocks flown in airplanes.
Starting with Paul Langevin in 1911, there have been numerous explanations of this paradox, all based upon there being no contradiction because there is no symmetry — only one twin has undergone acceleration and deceleration, thus differentiating the two cases. One version of the asymmetry argument made by Max von Laue in 1913 is that the traveling twin uses two inertial frames: one on the way up and the other on the way down. So switching frames is the cause of the difference, not acceleration per se.[1]
Other explanations account for the effects of acceleration. Einstein, Born and Møller invoked gravitational time dilation to explain the aging based upon the effects of acceleration.[2] Both gravitational time dilation and special relativity are needed to explain the Hafele-Keating experiment on time dilation using precise measurements of clocks flown in airplanes.

I still see a paradox. The travelling twin is travelling from his landed twin frame of reference, and switch of frames, as well as acceleration is relative, because for the travelling twin, the one changing frame of reference or experiencing acceleration is the other one. Right?

 

[Hielor]

I still see a paradox. The travelling twin is travelling from his landed twin frame of reference, and switch of frames, as well as acceleration is relative, because for the travelling twin, the one changing frame of reference or experiencing acceleration is the other one. Right?

No, you are "aware" that you are the one accelerating. It's only velocity (a non-accelerated frame of reference) where it's equivalent both ways.

 

[jedidia]

The travelling twin is travelling from his landed twin frame of reference, and switch of frames, as well as acceleration is relative, because for the travelling twin, the one changing frame of reference or experiencing acceleration is the other one. Right?

pretty much what Hielor says: accelerating means applying energy. This application can be measured. So if the twin on earth does a measurement, he can clearly proove that he is not accelerating, hence it must be his brother in the spaceship.

On the other hand, if the one in the spaceship does a measurement, he can clearly conclude at which rate he is accelerating, and can therewith conclude that his brother on earth is not. Hence, the situation is not symmetrical.

 

[the.punk]

I still see a paradox. The travelling twin is travelling from his landed twin frame of reference, and switch of frames, as well as acceleration is relative, because for the travelling twin, the one changing frame of reference or experiencing acceleration is the other one. Right?

There is no travelling twin. You also could say the earth is travelling away from the ship. When you are not accelerating and deccelerating. Both systems are a inertial system. Look what I said. And what Hielor said is also right.

---------- Post added at 10:08 AM ---------- Previous post was at 10:05 AM ----------

If you don't deccelerate both systems are equvalent. But you must deccelerate to arrive at earth and then you age slower as earth.
Look in the wikipedia link I posted. There is a diagramm about this.

 

[kneejo]

speed in space is usually relativistic to another object.. so what does this mean for the absolute speed of space itself? it can't be relative to anything, assuming space is all there is. and what does this mean for time? is there no such thing as absolute time, and could we live forever if we find a place in space that has no absolute speed, and therefore no time..

just a thought..

 

[the.punk]

speed in space is usually relativistic to another object.. so what does this mean for the absolute speed of space itself? it can't be relative to anything, assuming space is all there is. and what does this mean for time? is there no such thing as absolute time, and could we live forever if we find a place in space that has no absolute speed, and therefore no time..

just a thought..

There is no absolute time.
Time is relative. And when I travel near light speed I would't notice that time slows down. Because you can only have a speed to and other observer. I don't understand what you mean with "absolute speed of space". There is no absolute speed.

 

[kneejo]

well, the speed of the fabric of space itself, hypothetically.. considering all mass and light moving at speeds relative to each other.. how about relative to space itself.. apart from the expansion of everything.. but maybe space is included in the expansion. What about the movement of the hypothetical "bubble" we call the universe in some medium we can't understand yet..

wouldn't that speed be the origin of our concept of entropy, wich is in fact the result of a sort of absolute time-base.. relativistic in this universe only, quite absoluut when seen from outside the universe..

so time can vary, within this universe, because it is relative to the particular place in the universe.. I'm theorizing the idea of the regions outside the universe.. where time doesn't exist due to absence of mass or energy, if I understand this theory correctly.

 

[the.punk]

well, the speed of the fabric of space itself, hypothetically.. considering all mass and light moving at speeds relative to each other.. how about relative to space itself.. apart from the expansion of everything.. but maybe space is included in the expansion. What about the movement of the hypothetical "bubble" we call the universe in some medium we can't understand yet..

wouldn't that speed be the origin of our concept of entropy, wich is in fact the result of a sort of absolute time-base.. relativistic in this universe only, quite absoluut when seen from outside the universe..

so time can vary, within this universe, because it is relative to the particular place in the universe.. I'm theorizing the idea of the regions outside the universe.. where time doesn't exist due to absence of mass or energy, if I understand this theory correctly.

Well. You are talking of places outside the universe...there is nothing.
Physicists say this because all our physical laws apply for places inside our universe. And because of that we say there is nothing outside the universe.
And to original problem with the speed to the space itself:
You can only have a velocity to an relative observer. You can't speak of a speed to the universe because the space is nothing to that you can have a velocity like galaxys or a star or any other objects. A star is in the universe but the universe is in nothing. You cannot looks outside the universe to look what velocity I have.

 

[kneejo]

Well. You are talking of places outside the universe...there is nothing.
You cannot looks outside the universe to look what velocity I have.

naturally! but doesn't most scientific thought start with imagining what might possibly be at some place we cannot see yet? Speculation and assumption are the basis of many theories, that later on are sometimes proved to be correct. Even today's science is full of assumptions, that this-and-this particle might exist because we see such-and-such effect.. and then we discover those particles..

When thinking about time, I thought, there must be some kind of absolute time to the universe, because the process of entropy requires a more-or-less linear time structure. The entire theory we have to day about the birth of the universe needs time. So I wondered if we can figure out this universal time, we can also figure out what might be outside the universe, since the theories about time require the universe itself to have a relative speed in relation to this 'nothingness' which might not be nothing at all.. Just some ideas..

 

[Mindblast]

A real 'nothingness' would imply the absence of dimensions as well, hence no relative speed. After all the dimensions are the very groundwork of our universe, there just is no 'outside' in any way imaginable as this relys on the concept of our known dimensions, which is only valid within our universe. Just my two cents..

 

[the.punk]

naturally! but doesn't most scientific thought start with imagining what might possibly be at some place we cannot see yet? Speculation and assumption are the basis of many theories, that later on are sometimes proved to be correct. Even today's science is full of assumptions, that this-and-this particle might exist because we see such-and-such effect.. and then we discover those particles..

It's just like you say. We can only can speculate what outside the universe is...But for today we cannot prove what outside the universe is.
And then the most logical is there is nothing.
And also all our theories are made for the universe and not outside.

When thinking about time, I thought, there must be some kind of absolute time to the universe, because the process of entropy requires a more-or-less linear time structure. The entire theory we have to day about the birth of the universe needs time. So I wondered if we can figure out this universal time, we can also figure out what might be outside the universe, since the theories about time require the universe itself to have a relative speed in relation to this 'nothingness' which might not be nothing at all.. Just some ideas..

A good thought, though.
But as far as I think the the basic idea of the theory of relativity is that there isn't a absolute time.

 

[JamesG]

You can think of the expansion of the universe (since the "big bang") as the baseline velocity and therefore time of everything in relation to each other. So from an observer sitting serinly in interstellar space above the Milky way at a universal time/speed dead stop, would see the Sol system whirl by slowly, but a star wizzing around the galactic core would be slower still. If wonder if that "time gradent" has an effect on shape of galaxies?