Re: tensile strength of space-time

[brian whatcott <inet@INTELLISYS.NET>]

At 10:09 11/8/99 -0700, you wrote:
> We're discussing elastic properties of solids right now
> and one student asks:
>
> Can the tensile (or shear) strength of space-time be
> measured based on how
> much it bends due to gravity?
>
> What say ye?
> Thanks,
> Larry

This was a haunting question. I don't recall any replies.
 I could say that tensile force is a measure of how much force
a particular sample could bear without suffering permanent deformation.

I think I know how to measure the distortion of space time - and
that is by sampling it with a precise clock to gather a cumulative
time difference between the sample space and the reference space.

But I don't know how to remove the force that bends the space-time -
which is provided by the mass of a body. I can't think of a way to
switch it off.

It appears that electromagnetic effects cannot penetrate an event
boundary surrounding a black hole - but it not clear to me that
this horizon shuts off the influence of gravity: I suppose not.
 So I cannot simply check for ST distortion then shove the object
of interest through such an horizon, to see that some time
dilation is completely countermanded.

Is there some other way, I wonder, to sense a non linear distortion?
One immediately bridles at that adjective: 'non-linear'.
   The impression I have is that the efffect of gravity is always
 non linear - so that like a metal such as aluminum which also
 has no perfectly linear stress/strain region one needs to define a
limit for acceptably small distortion, like the 0.1% yield stress
often used to characterize such alloys.

And so one ponders the question, is there some region where like
a metal, an increasing force produces more and more extension or
deflection until the sample parts in two?


Remembering that gravity is always attractive, the comparison
would need to be with a compressive failure like that of a bullet
hitting a steel plate: the lead bulges and spreads while its ends
come close.

And here, I suppose the descriptions one reads of a stellar collapse
so that normal matter condenses to neutrons represents a comparable
compressive failure.    It seems that the requisites for this collapse
have indeed been calculated, so that the limit for compressive strength
for matter in spacetime is given as so many Solar masses in the limit.

On this basis, Larry could answer in the affirmative this question:

> Can the tensile (or shear) strength of space-time be measured
> based on how much it bends due to gravity?







brian whatcott <inet@intellisys.net>
Altus OK