# So if space/time is a plain

1. Jul 3, 2011

### Twigsoffury

So if space/time is a "plain"...

from what i get of it, space and time is a flat surface, and the planets and what not ride along the rings of the depressions made in it. The more i'd guess "dense" a object is, the bigger the depression and the higher gravitational pull it has.

Now how in the hell do asteroids fly in from "above" our planet and why are there stars in every direction possible if its supposed to be a flat plain.

and couldn't we cheat by creating a super dense object under our space ship and sorta skip above the "space-time" making it depress for millions of years?

or would be just fall in that deep a@# hole?

Last edited by a moderator: Jul 3, 2011
2. Jul 3, 2011

### Staff: Mentor

Re: So if space/time is a "plain"...

It is not that spacetime is a flat plain, it is just that it is difficult to draw an accurate representation of a curved 4D spacetime on a flat 2D piece of paper.

3. Jul 3, 2011

### Matterwave

Re: So if space/time is a "plain"...

Space-time is 4-D, and it "curves". The only way to "see" a curvature is embedding in a flat 1 higher dimension diagram, so to see a 4-D space-time curve you need to embed the space-time in a 5-D diagram. We can't draw 4-D, let alone 5-D.

So what people usually do is take a 2-D slice of the space-time (by, for example keeping 2 of the dimensions "constant"), and embedding it in a 3-D diagram. This is what you see in those illustrations. It doesn't mean in any way that space-time is a 2-D plane though.

Last edited by a moderator: May 5, 2017
4. Jul 3, 2011

### danR

Re: So if space/time is a "plain"...

That membrane with the depressions has made as much confusion over the decades as enlightenment.

But you have way with words, and I hope you keep posting, and go tell the membrane-explainers to stick that sheet where the moon don't shine.

5. Jul 4, 2011

### GrayGhost

Re: So if space/time is a "plain"...

Interesting. I am not preficient in GR, but I would guess that density makes the hillside steeper, but I'm not sure it would make the bottom deeper. The experts here will likely weigh in in that respect. Depth would be considered the potential, and the steepness the gradient. I suspect that the gradient dictates the strength of gravity at any point in spacetime, not the depth. No doubt about it though, for any given quantity of mass, the denser the mass the steeper the gradient, and so the stronger the gravitation would be at its strongest location.

As mentioned, spacetime is 4 dimensional, flat or not. The 2d surface is only an anology to make the geometry easier to understand. Spacetime is 4 dimensional, and so a flat spacetime is a flat volume. Look at it this way ... a volume with no density variation within it. In any local area of the cosmos, in regions far from gravity source, spacetime seems uniform (or flat). In grandier though, the cosmos is curved. In analogy, the earth seems flat when considered only locally.

Well, there is no above or below spacetime. One is in spacetime all the time, and there is no escape. Using gravity produced by a mass has it problems ... you fall to it while it falls to you, then you collide. Better to use high energy to create the dent in spacetime ...

In star trek, the warp drive has enough energy to warp the very fabric of spacetime, which dents it as a dead star would. So energy is used to warp spacetime instead of mass. Of course, we're talking Hollywood here. Yet in theory, it's possible. Warp the spacetime in your neighborhood, and time passes by slower for you (than for others) if you are in the dent (and they are not). The dent pulls your toward its bottom (ie gravity), and you forever remain on its hillside. The cosmos passes by and ages very fast, while you age less. It's like riding the surf, and you carry the wave with you as you go. Go fast enough, and millions of years can pass on earth that do not pass for you. Hence, you probably would not want to go "too fast".

The warp drive is fixed within specific remote parts of the ship. The warp bubble (so to speak) encompasses the entire ship. You keep falling into the hole you create as you go ... keep the wave right where it needs to be for best results :) You never fall to the bottom, however you are always falling toward it though, forever keeping the bottom out in front of you such as to keep falling. The moon always falls to earth at 1/16" every second per sec, but the earth's curvature curves away at (about) the same rate, keeping the moon in its orbit. Same deal with warp drives, but a much stronger gravity well.

GrayGhost

Last edited: Jul 4, 2011