# Thread: Relativity and what happens when you STOP moving.

1. Hello, this is my first post

I heard that the faster something moves, the larger it's mass and the slower time passes, relative to observers.

Also, I'd heard that it takes an infinite amount of energy to reach the speed of light by conventional means.

However, something I've never noticed people talking about is the speed that we are already travelling.
We are not technically still, are we? The earth is spinning around the sun, the solar system is hurtling through the galaxy, and the galaxy is speeding outwards from the centre of the universe?

This means, if we fly in the direction that the galaxy is moving, won't we technically have a combined speed much higher than commonly stated? Relative to the centre of the universe, of course.

Since light is absolute and not travelling along with us, aren't we're a lot closer to the speed of light already?

My question is three fold.

Firstly, if we are moving already, on a galactic scale, does moving in the same direction make an object's true speed much greater, relative to the centre of the universe, than to the earth? If this is so, is a rocket travelling closer to the speed of light than it's sensors can record?

Secondly, my understanding of E=MC2 is that more speed increases energy and mass. Does this mean gravity too?
Could an object the size of a football acquire the mass, and therefore gravitational influence of something much larger?

Lastly, this is the one that really interests me. The way I understand it, going faster increases an object's mass.
Since everything is moving away from the centre of the universe, does everything have an energy and mass relative to the speed we are moving away from it?

What would happen if I jumped into a remarkably powerful spacecraft and did an all-stop. I mean, stopping so that, relative to the centre of the universe, I wasn't moving at all. What would happen to my mass? Assuming the universe is 'everything' and isn't moving itself.

Would mass and energy become zero? Would time behave oddly? After all, it slows down as you speed up. If you stopped, would it pass incredibly quickly relative to the matter hurtling away from the centre of the universe?

My sincerest apologies if this makes no sense and I've been talking out of the wrong orifice.

Still, that is my, albeit crude understanding of things and I'd like to know if it means anything to more knowledgeable people in the field.

Oh, and one more thing:
If you are accelerating towards to centre of the universe, aren't you technically Decelerating, are you are already moving in the opposite direction?

2.

3. Originally Posted by cyberkilla
Hello, this is my first post

I heard that the faster something moves, the larger it's mass and the slower time passes, relative to observers.

Also, I'd heard that it takes an infinite amount of energy to reach the speed of light by conventional means.

However, something I've never noticed people talking about is the speed that we are already travelling.
We are not technically still, are we? The earth is spinning around the sun, the solar system is hurtling through the galaxy, and the galaxy is speeding outwards from the centre of the universe?

Actually, technically there is no centre of the universe, nor; is the galaxy from what we could call the centre. Instead space (the nothingness) is expanding; but for the purpouses of your question, it is easier to assume this "centre" as a point of reference.

This means, if we fly in the direction that the galaxy is moving, won't we technically have a combined speed much higher than commonly stated? Relative to the centre of the universe, of course.

Mmm, no because we wont reach the speed of light, whether or not we already have momentum, and the speed that we are already moving it is quite slow compared with C.

Since light is absolute and not travelling along with us, aren't we're a lot closer to the speed of light already?

Closer than being absolutely still yes, but nowhere near close enough.

My question is three fold.

Firstly, if we are moving already, on a galactic scale, does moving in the same direction make an object's true speed much greater, relative to the centre of the universe, than to the earth? If this is so, is a rocket travelling closer to the speed of light than it's sensors can record?

Yes, this is true. For speed/velocity to be recorded we need a fixed point in space to use it as a reference; whether that fixed point be a position on a wheel (in a car) or fairly static air (in a plane). I am unsure how speed could be measured in space; other than by using radio-relay and detecting how long it takes for the signal to come back once transmitted and then to do the same transmission again and work out your relative speed from the difference; but if the transmitter is on a sattelite or on earth (which is moving) then yes, the reading becomes inaccurate.

Secondly, my understanding of E=MC2 is that more speed increases energy and mass. Does this mean gravity too?
Could an object the size of a football acquire the mass, and therefore gravitational influence of something much larger?

Lastly, this is the one that really interests me. The way I understand it, going faster increases an object's mass.
Since everything is moving away from the centre of the universe, does everything have an energy and mass relative to the speed we are moving away from it?

What would happen if I jumped into a remarkably powerful spacecraft and did an all-stop. I mean, stopping so that, relative to the centre of the universe, I wasn't moving at all. What would happen to my mass? Assuming the universe is 'everything' and isn't moving itself.

Im not too sure what you mean here. Your mass would decrease of course, but it would never be zero because of latent energy.

Would mass and energy become zero? Would time behave oddly? After all, it slows down as you speed up. If you stopped, would it pass incredibly quickly relative to the matter hurtling away from the centre of the universe?

Time dilation only becomes practically noticable very near the speed of light. Time is also relative to motion, so without motion, there is no time.

My sincerest apologies if this makes no sense and I've been talking out of the wrong orifice.

Still, that is my, albeit crude understanding of things and I'd like to know if it means anything to more knowledgeable people in the field.

Oh, and one more thing:
If you are accelerating towards to centre of the universe, aren't you technically Decelerating, are you are already moving in the opposite direction?

No there is no centre - see above

4. So space is expanding, not just the objects within it?

Also, if we are moving, whether it's away from a central point or not...
What *would* happen if we were able to stop. And I mean totally.

Are our perceived masses and gravities attributed, in part, to the fundamental expansion of the universe?

What I mean is, would the earth have less gravity if it wasn't falling around the sun, and the solar system wasn't moving around with the galaxy, and so on?

Lastly, if the acceleration of the universe increases, would matter take on more and more mass?

I assume the expansion of the universe does involve movement of matter, as systems are slowly moving apart.

If it was space which was expanding, surely even atoms would be moving further apart? I read that, "the further a galaxy is from another, the faster it is moving away." So, on the atomic scale, the speed at which the atoms are moving apart must be tiny? Perhaps other forces are able to compensate for the moving apart. Perhaps it only makes sense in my head
Still, they say the big crunch is when the universe stops expanding. If it did, perhaps the atoms fall together because the outward force of universal expansion between each one isn't enough to counteract the other forces. No, that can't be right. I'm making things up now

EDIT:
According to: http://en.wikipedia.org/wiki/Metric_expansion_of_space
I was actually correct, in part, about expansion affecting matter on the small scale.
Gravitational forces, etc, keep matter together, but on a cosmological scale, things are different.
I'd be interested to know whether it affects things on the atomic scale too, however. For instance, if it is actual space-time which expands, would the distance between the nucleus of an atom and it's orbiting electrons be affected? What about the nucleus itself?
The expansion is impossibly small at that scale, but does it still exist. Interesting.

5. Actually, you can never detect your own relativistic mass or your own length contraction or time dilation. You can only detect those things in other objects moving relative to you.

Edit: And yes, even atoms are moving apart, although slowly, at that scale. Look up the Big Rip as one possible consequence of this.

6. Originally Posted by cyberkilla
So space is expanding, not just the objects within it?

Yes, space is expanding. To give you a fairly good example of this, get a baloon and draw two dots on each the balloon exactly 1cm apart. Now, blow air into the balloon and measure the distance between the two dots. It will be more than 1cm. The dots themselves have not moved relative to the space on the surface of the balloon they occupy; instead what has happened is that the space between them (i.e the balloon) has expanded.

Also, if we are moving, whether it's away from a central point or not...
What *would* happen if we were able to stop. And I mean totally.

This depends on what you mean by totally stop. Stop travelling? - and you would just appear to be motionless but your heart is still beating and blood is being pumped round your body so without dying you could never be completely still. Further more to that the atoms and molecules that make up your body are never still, they are ALWAYS moving.

Are our perceived masses and gravities attributed, in part, to the fundamental expansion of the universe?

Possibly. Possibly not. We do not know.

What I mean is, would the earth have less gravity if it wasn't falling around the sun, and the solar system wasn't moving around with the galaxy, and so on?

No, gravity it is believed is due to matter distorting and curving space. Possibly it can also be united with electric forces, but we are not sure of this yet b]

Lastly, if the acceleration of the universe increases, would matter take on more and more mass?

No, remember it is SPACE that it is expanding and not matter.

I assume the expansion of the universe does involve movement of matter, as systems are slowly moving apart.

If it was space which was expanding, surely even atoms would be moving further apart? I read that, "the further a galaxy is from another, the faster it is moving away." So, on the atomic scale, the speed at which the atoms are moving apart must be tiny? Perhaps other forces are able to compensate for the moving apart. - You are absolutely correct here !! - However because the rate of expansion or space or "EOS" as we call it is INCREASING, there will come a time when the pull of expansion is so great that the atomic forces will no longer be able to cope withstanding the pressure and all atoms will literally be shredded apart. Perhaps it only makes sense in my head
Still, they say the big crunch is when the universe stops expanding. If it did, perhaps the atoms fall together because the outward force of universal expansion between each one isn't enough to counteract the other forces. No, that can't be right. I'm making things up now

EDIT:
According to: http://en.wikipedia.org/wiki/Metric_expansion_of_space
I was actually correct, in part, about expansion affecting matter on the small scale.
Gravitational forces, etc, keep matter together, but on a cosmological scale, things are different.
I'd be interested to know whether it affects things on the atomic scale too, however. For instance, if it is actual space-time which expands, would the distance between the nucleus of an atom and it's orbiting electrons be affected? What about the nucleus itself?
The expansion is impossibly small at that scale, but does it still exist. Interesting.

7. Remarkable. Thank you, I appreciate the two of you responding.

Taking on-board what you've told me, I have one final question for now

As you've mentioned, the universe is expanding, but it's the space itself, not the matter which is changing scale.

However, the matter is 'on the balloon' and it's relative coordinates shift as a result of the expansion.

Should I regard the movement of galaxies away from each other as a physical movement, complete with a notable velocity, time differentials, greater mass(relative to the same galaxy travelling more slowly), etc, as one would regard the movement of a rocket?

Or, does it have more in common with a vessel using a Warp Drive, in that it's a warp in space. Not actually travelling through space, but travelling on space through it's warping/expanding? Sitting on the starship enterprise, it can pass light speed because it technically isn't. It's riding a warp in space-time.

I hope that makes sense. It's just that an article on Wikipedia states that 'the speed of light has no special significance with regards to [the expansion of the universe]'.
The matter that is moving apart can move and occupy the new space created as the universe expands, but if it stays in the same place, is it really moving even if it's observable position changes?

8. I think it would be more like a warp drive. Look up the Alcubierre drive. The expansion still causes a redshift in light, just like relative motion would, but when the expansion gets fast enough, you won't be able to see stars anymore. The light isn't going fast enough to ever reach you. Of course, that's getting pretty close to when matter starts falling apart, IIRC.

9. Thanks, I think I understand now

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