Another data across long distances (nearly) instantly theory

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

User avatar
J Spade
Luppoewagan
Posts: 523
Joined: Wed Apr 18, 2007 7:56 pm UTC
Location: Up a creek without a paddle
Contact:

Another data across long distances (nearly) instantly theory

Postby J Spade » Sat May 24, 2008 7:37 pm UTC

Imagine a very long string or cable that is attached to two stations very far from each other (maybe a light year, but doesn't matter.)

Now if someone at station 1 pulled on the cable, someone at station 2 would notice it instantly, would they not? (assuming it does not stretch)
Could this be used to transmit data faster than light?

User avatar
ATCG
Posts: 471
Joined: Sat Aug 18, 2007 3:44 am UTC
Location: Straight up the jω axis

Re: Another data across long distances (nearly) instantly theory

Postby ATCG » Sat May 24, 2008 7:50 pm UTC

Here is one of the threads discussing why this doesn't work.
"The age of the universe is 100 billion, if the units are dog years." - Sean Carroll

User avatar
Gammashield
Posts: 68
Joined: Fri Jun 29, 2007 7:41 pm UTC

Re: Another data across long distances (nearly) instantly theory

Postby Gammashield » Sat May 24, 2008 7:50 pm UTC

That argment isn't giving a data transmission method sadly. Rather, what you've got there is a quick thought experiment that shows there's no such thing as a 'perfectly rigid' object. A side consequence of special relativity is that *any* material, unobtanium or otherwise, has some minimum compressability/extendability dictated by the speed of light. Compression waves in an object (aka, sound, or tugs/pushes) have a theoretical cap speed of the speed of light.

As a practical matter, of course, that speed is usually much, much lower.

Mettra
Posts: 96
Joined: Tue Apr 29, 2008 1:37 am UTC

Re: Another data across long distances (nearly) instantly theory

Postby Mettra » Sat May 24, 2008 8:19 pm UTC

*Chime in for agreement*

When you push that rod, what you are doing is pressing the atoms on the outside of it into the atoms right beside them. Those in turn press the atoms next in line and so on until you get to the end of the rod. Atoms cannot move faster than (or as fast as) light. This explanation is usually simpler to understand than Young's modulus and talks of rigidity.
zenten wrote:Maybe I can find a colouring book to explain it to you or something.

TheCoelacanth
Posts: 49
Joined: Mon Dec 10, 2007 12:07 am UTC

Re: Another data across long distances (nearly) instantly theory

Postby TheCoelacanth » Sun May 25, 2008 12:19 am UTC

Good luck making the unstretchable cable.

User avatar
taby
Posts: 154
Joined: Thu Nov 01, 2007 8:39 pm UTC
Location: Canada

Re: Another data across long distances (nearly) instantly theory

Postby taby » Sun May 25, 2008 3:06 am UTC

The point here I think is that the interactions within the rod are heat conduction (also known as momentum, or energy flux), pressure (aka momentum flux), viscosity (aka momentum diffusion), and gravitation.

Since heat conduction is performed by photons, it's seen that the maximum rate that a change in temperature may transfer through the rod is c metres per second (according to special relativity). Photons also carry pressure, limiting the transfer of pressure to a rate of v = c. Likewise for the transfer of viscosity.

That said, even when the rod is modeled as a pressureless perfect fluid (no momentum or any of its derivatives), and gravitation is the only interaction worth considering, changes in the gravitational field still only transfer at v = c (according to general relativity).

So really, there is no way for change to transfer through the rod at a velocity faster than c (according to modern relativity).


Return to “Science”

Who is online

Users browsing this forum: No registered users and 13 guests