MadSci Network: Physics Query:

### Re: Why can't we warp the space time continuum??

Date: Sun Nov 12 10:13:36 2000
Posted By: Dan Mayer, Post-doc/Fellow, Mathematics and Theoretical and Particle Physics, I am currently out of work.
Area of science: Physics
ID: 968551309.Ph
Message:
```
Space-time can be curved. It is curved by mass (or energy) - this being
the source of gravity. To warp it very much, a huge amount of mass would
be required - this is what happens in a Black Hole.

If you drew a circle on a flat piece of paper, and measured the radius and
the circumference, you would hope to find that
radius = circumference / 2*pi.
What if you were not aware of height, but lived on the Earth. You could
draw the equator - a circle. The radius should be measured from the centre
of the Earth. But being unaware of the fdirection 'down', you would
measure the radius from the North Pole. This would be much larger than the
actual radius. When you divided the equator (your circumference) by 2*pi,
you would find that your measured radius was much bigger than your
expected radius. There is an excess radius because the Earth's surface -
your space - is bent.

The surface area of a sphere is A=4*pi*(r^2). If you measured the surface
Area, you would expect to predict the radius, r=sqrt(A/(4pi)).
...unless, that is, our space-time is warped. In this case, there may be
= GM/(3c^2),
where G is Newton's Gravitational Constant, c is the speed of light, and M
is the mass inside the sphere (assumed to be evenly distributed).
G/3c^2 has a value of about 2.5*10^-29 cetimetres per gram, so for each
gram, there is an excess radius of about 2.5*10^-29 cm.
As you can see, a lot of energy is needed to warp space-time by a large
amount.

I suggest you read 'Hyperspace' by Michio Kaku for a godd account of this
area, or perhaps 'Six Not-So-Easy Pieces' by Feynman, whose explanation of
General Relativity I have just given you.

```

Current Queue | Current Queue for Physics | Physics archives