# Space Time in a smaller scale.

1. Mar 31, 2005

### Prague

Space time question.

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

Does space time only exist in space? If so, is earths 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?

Last edited: Mar 31, 2005
2. Mar 31, 2005

### Phobos

Staff Emeritus
Welcome to Physics Forums!

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).

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

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

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.

3. Mar 31, 2005

### 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, whats the theory about opening worm holes? Is there one, or is it just random occurances (if it was possible of course).

4. Apr 1, 2005

### 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!!!

5. Apr 1, 2005

### SpaceTiger

Staff Emeritus
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.

6. Apr 1, 2005

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

Last edited by a moderator: May 2, 2017
7. Apr 1, 2005

### SpaceTiger

Staff Emeritus
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.

No, comets are much less tightly bound than humans.

Last edited: Apr 1, 2005
8. Apr 1, 2005

### 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 becuase 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?

9. Apr 2, 2005

### Nereid

Staff Emeritus
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; ...

10. Apr 2, 2005

### 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.

11. Apr 3, 2005

### Prague

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?

12. Apr 3, 2005

### 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.

13. Apr 3, 2005

### 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?

14. Apr 3, 2005

### 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.

15. Apr 3, 2005

### SpaceTiger

Staff Emeritus
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.

16. Apr 3, 2005

### Prague

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 feild 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?

17. Apr 3, 2005

### SpaceTiger

Staff Emeritus
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.

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).

18. Apr 3, 2005

### 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.

19. Apr 3, 2005

### 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.

20. Apr 3, 2005

### Prague

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.

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. :surprised