Is Space Time Only Relevant in Space?

[Prague]

Space time question.

Before I ask my question I suppose I should ask a preliminary question that will tell me if my actual question has an answer.

Does space time only exist in space? If so, is Earth's surface considered space, thereby abiding by space times rules? Also, theoretically if we were to bend space time we could travel 'through' space to get to another point. Now does this also relate to smaller scales such as if I was in space could I bend space time to allow me to travel say 50 feet away?

 

[Phobos]

Welcome to Physics Forums!

Does space time only exist in space?

The "fabric of the universe" (what the universe is made of) is space (3 dimensions) plus time (1 dimension). Space and time are closely linked, so they are sometimes referred to as one thing (spacetime).

If so, is Earth considered space,

The Earth is a collection of matter/energy that moves through space and time.

thereby abiding by space times rules?

Every atom or subatomic particle of the Earth is tied to spacetime and must play by its rules.

Also, theoretically if we were to bend space time we could travel 'through' space to get to another point. Now does this also relate to smaller scales such as if I was in space could I bend space time to allow me to travel say 50 feet away?

There is a mathematical solution to some of Einstein's equations that indicate such "wormholes" are possible (a shortcut tunnel through space...could be 50 feet or 50 light years). But none have been proven to actually exist.

 

[Prague]

Ok, thanks, now to the real question. If everything has to abide by these rules, would it not be possible to bend space on the surface of the earth? I think– but I am not sure– that the belief is that if you can accumulate something that has enough mass it distorts space time, correct? If so, wouldn't we be able to distort the time on our planet as well? Perhaps if we created something that was small but weight more than the Earth (somehow suspending it) wouldn't we be able to slow time? Also, what's the theory about opening worm holes? Is there one, or is it just random occurances (if it was possible of course).

 

[primal schemer]

I`m no expert, but I think if there was something (for example a black hole) that was massive enough to effect our time in any substantial way, the gravitational force would be huge and we would be sucked into it. This would not be good!

 

[SpaceTiger]

I`m no expert, but I think if there was something (for example a black hole) that was massive enough to effect our time in any substantial way, the gravitational force would be huge and we would be sucked into it.

Actually, the big problem with standing near small black holes is tidal forces. The difference in force between one end of our body and the other would rip us apart.

 

[primal schemer]

How near would you have to be and how large would gravity have to be for tidal forces to rip you apart??

I found here: http://seds.lpl.arizona.edu/sl9/sl9.html
that when orbiting Jupiter a comet broke apart due to tidal forces. Does this mean that humans could never go too close to Jupiter?

 

[SpaceTiger]

How near would you have to be and how large would gravity have to be for tidal forces to rip you apart??

That depends on the strength of our various body parts. In the Newtonian approximation, the force is given by

F_t=\frac{2GMm}{r^3}L

where L is the length of our body. If the object is a black hole, this goes to:

F_t=\frac{c^6m}{4G^2M^2}}L

at the event horizon. As I said, however, that's only an approximation.

that when orbiting Jupiter a comet broke apart due to tidal forces. Does this mean that humans could never go too close to Jupiter?

No, comets are much less tightly bound than humans.

 

[Prague]

Well, could you not create an object with small mass but enormous weight? If so, that wouldn't have any affect on bending space time because the weight is not what bends it. Therefore, how would you give a certain object a gravitational force? Also, is it possible to even create an object where mass is small but weight is enormous?

 

[Nereid]

Well, could you not create an object with small mass but enormous weight? If so, that wouldn't have any affect on bending space time because the weight is not what bends it. Therefore, how would you give a certain object a gravitational force? Also, is it possible to even create an object where mass is small but weight is enormous?

Hmm, seems to me there's some confusion about 'weight' and 'mass'. Simplifying somewhat, the 'mass' of an object remains the same, no matter where it is; the 'weight' of that object depends on how close it is to another object, and how much more massive that second object is. For example, taking your 'weight' on the Earth's surface as 1, then on the Moon's surface, your weight will be ~0.16; on an asteroid, ~0.01 (or less); out in 'deep space', ~0.000000[lots of 0's]001; ...

 

[tony873004]

If we could create something on Earth that was as massive as the Earth, most our man-made satellites would instantly come crashing down. The Moon would have its perigee lowered to about 100,000. Creating enormous tides.

After the experiment, when getting ready to destroy our earth-massed object, we'd have to time it just right. If we destroy it when then Moon is anywhere in its orbit other than apogee, the Moon would escape the Earth, and become an Earth-crossing planet.

 

[Prague]

If we could create something on Earth that was as massive as the Earth

I meant as heavy, it could be the size of a pea though. Anyways, if this were possible and we could take care of all the apocalyptic dangers, (now the object is the size of a pea but the weight is 10 times that of the earth, and we have somehow suspended it), would time be distorted around it? Would it slow down?

 

[Grogs]

Actually, the gravity of the Earth *does* warp space time. Although the warping is negligably small most of the time, certain applications like GPS satellites have to consider this effect.

You should note though that this difference is observer dependent though. You wouldn't notice your clock running fast unless you could compare it to someone who wasn't affected by the same gravitational warping.

 

[Prague]

So, is it possible to create something that distorts time enough to make a difference? If so, would it also be possible to create it on the Earth (avoiding the apocalyptic dangers listed before)?



oh, and I've been saying throughout this thread "what if we could create something the size of a pea but 10 times heavier than earth." Is it even possible to create a small object that is very heavy? I know certain metals weigh more but those weight differences aren't anything special. Like at the present time could we create something the size of a pea that perhaps weighed 100 pounds?

 

[Grogs]

1) Well, I don't think you can get a whole lot more dense than the densest of metals with normal materials. Beyond a certain point, the electron fields in the atoms will repel each other. The only way to get more dense than that and make it stay together would be to make a black hole.

2) What do you mean by 'make a difference'? Do you mean a wormhole that allows us to go from one point to another instantaneously? If so, I think Einstein's wormholes call for a black hole at the entry and exit point (or maybe a white hole at the exit.) If our theories are correct, making even the smallest possible black hole is many, many orders of magnitude beyond our current technology.

 

[SpaceTiger]

So, is it possible to create something that distorts time enough to make a difference?

If you're talking about using black holes as a sort of forward time machine to keep a human from aging relative to the outside world, then no. Any black hole massive enough to do that would also be massive enough to tear us to shreds.

It would be interesting to ponder the possible uses of black holes in particle physics experiments, however. If we could create a low-mass BH, then presumably we could collide particles near its event horizon and observe otherwise short-lived states. Also, sci-fi writers have had fun speculating on the possible use of black holes as an energy source. It turns out that it's almost maximally efficient at turning mass into energy.

 

[Prague]

If you're talking about using black holes as a sort of forward time machine to keep a human from aging relative to the outside world, then no. Any black hole massive enough to do that would also be massive enough to tear us to shreds.

Yes, that is what I was trying to get at, I just didn't want to come straight out and say it because I wanted to avoid the black hole issue. So I suppose we cannot create something that can alter time and still allow us to survive. If we could I suppose that would be usefull, make its time distortion field large enough to cover an area and you can have a civilization that will never die– or age for that matter– so I suppose you would have to find a way to send children to another "time distortion" planet which could let them age until a specific time and then they go back to the civilization. But that would lead to population problems ect... (pure scifi rant)

Oh, that brings another question I could ask, if you were to strip away all the objects that cause time distortion, what would the time be?

 

[SpaceTiger]

Yes, that is what I was trying to get at, I just didn't want to come straight out and say it because I wanted to avoid the black hole issue.

To achieve the effect you're looking for, it would be much more energy efficient to accelerate people to near the speed of light. They would experience the same time dilation effects, but without the unpleasantness of being torn to shreds.

Oh, that brings another question I could ask, if you were to strip away all the objects that cause time distortion, what would the time be?

It would appear the same as now, but without the distortions in other objects. Remember that in relativity everything always appears normal in your reference frame (if it's inertial).

 

[Chronos]

The Pauli exclusion principle greatly limits the maximum density of ordinary matter. Osmium [or possibly iridium], specific gravity 22.57, is the densest known element. To achieve denser states you must either jettison electrons [electron orbits are enormous compared to the size of the atomic nucleus], or force them out of their normal states. This of course leaves you with a decidedly non-ordinary form of matter known as degenerate matter. Degenerate matter can only exist under extreme conditions such as those found on collapsed stars - e.g., white dwarfs and neutron stars. This is not a stable form of matter and any attempt to mine and carry off a chunk of such a star would end badly. As soon as your 'ore' left the intense gravitational field of the star, the Pauli exclusion principle would reassert itself and your 'neutronium' would revert back to a non-degenerate state - and rather spectacularly if you pulled it away really fast.

 

[Prague]

To achieve the effect you're looking for, it would be much more energy efficient to accelerate people to near the speed of light. They would experience the same time dilation effects, but without the unpleasantness of being torn to shreds.

Why would this slow your aging process? Wouldn't you still die after say 85 years of aging? Why do you not age if you are traveling fast?


Well, if I were to understand this, which I dont, I suppose you would die since you can't reach the speed of light, so if you are traveling 99.9999c you would only experience .00001% of a second for every second. So you would die after a really, really long time.

 

[Prague]

Why would this slow your aging process? Wouldn't you still die after say 85 years of aging? Why do you not age if you are traveling fast?

Well, if I were to understand this, which I dont, I suppose you would die since you can't reach the speed of light, so if you are traveling 99.9999c you would only experience .00001% of a second for every second. So you would die after a really, really long time.

The Pauli exclusion principle greatly limits the maximum density of ordinary matter. Osmium [or possibly iridium], specific gravity 22.57, is the densest known element. To achieve denser states you must either jettison electrons [electron orbits are enormous compared to the size of the atomic nucleus], or force them out of their normal states. This of course leaves you with a decidedly non-ordinary form of matter known as degenerate matter. Degenerate matter can only exist under extreme conditions such as those found on collapsed stars - e.g., white dwarfs and neutron stars. This is not a stable form of matter and any attempt to mine and carry off a chunk of such a star would end badly. As soon as your 'ore' left the intense gravitational field of the star, the Pauli exclusion principle would reassert itself and your 'neutronium' would revert back to a non-degenerate state - and rather spectacularly if you pulled it away really fast

So basically you can't do this because you would always have to have a gravitational force that compacts this matter into a small object? Well couldn't you create something that contains a gravitational force strong enough to do this and make it just as small as the object, or a little bigger so it can contain the object itselfs? It be like 6 billion people walking around with there immortality around their neck which if broken could destroy the world.

 

[SpaceTiger]

Why would this slow your aging process? Wouldn't you still die after say 85 years of aging? Why do you not age if you are traveling fast?

It would slow the aging process from the point of view of the stationary people on earth. However, the moving person would notice no difference.

Well, if I were to understand this, which I dont, I suppose you would die since you can't reach the speed of light, so if you are traveling 99.9999c you would only experience .00001% of a second for every second. So you would die after a really, really long time.

The equations don't quite work out that way, but the idea is basically right, as long as you keep in mind that the aging is only slowed from the point of view of the stationary observer.

 

[Prague]

It would slow the aging process from the point of view of the stationary people on earth. However, the moving person would notice no difference.




The equations don't quite work out that way, but the idea is basically right, as long as you keep in mind that the aging is only slowed from the point of view of the stationary observer.

Good, I was hoping you would say that. So actaully this wouldn't cause immortality, Because if the observer views the person as being immortal, it doesn't matter. Although his "image" is still there, he really isnt. He infact is dead 80 something years later but the images of his youthful self are still being received by the observer say some 10000 times slower which is why he looks so youthful.

(This brings me to an idea I have been discussing in another thread)

So you have man called A, a planet that the man lives on called H.

Now the year on H is 0 and A travels 30,000 light years away. This trip took him say 10 years, because he was traveling close to the speed of light. When he reaches the spot 30,000 light years away A declares it as X.

So the year on H when A reaches X is now 10 because it took A 10 years to get to X. H then decides he wants to go home after spending .5 of a year on X. So he goes home and it again takes him 10 years. Now A should be 20.5 years older, and the year on H should be 20.5. Is this not correct?

 

[Prague]

I think a thread I had in another section of PF answered this. The time relative to S is slower than the time relative to either X and E because \sqrt{1 - v^2/c^2}

Let me know if I am wrong, I just though that these concepts fit nicely so they may be right. Anyways, so actually relative to X and E, S is traveling 100,000 years? But S only experiences 44.7 years because actually his "clock" is slowed down although S still feels it is normal?

 

[primal schemer]

So you have man called A, a planet that the man lives on called H.

Now the year on H is 0 and A travels 30,000 light years away. This trip took him say 10 years, because he was traveling close to the speed of light. When he reaches the spot 30,000 light years away A declares it as X.

So the year on H when A reaches X is now 10 because it took A 10 years to get to X. H then decides he wants to go home after spending .5 of a year on X. So he goes home and it again takes him 10 years. Now A should be 20.5 years older, and the year on H should be 20.5. Is this not correct?

No, the time on planet H and the increase in age of person A will disagree. This is a version of the popular twins paradox (type it in google to get a mountain of relevant links). Imagine A has a twin (called B) that stayed on the home planet. on A`s return he would be YOUNGER than B. Not just because B cannot see the spaceship due to its speed, less time has actually passed for A.
If A carried a stopwatch with him, and started it when he left, and B did the same, the time on A`s stopwatch would be less than on B`s on his return.

So, it someone could travel at very close to the speed of light, then they could actually see the universe age. This could, in theory, lead us to travel thousands of years into the future (although getting back from the future would be an even bigger problem!).