Perfectly Rigid Bodies and Quarks

[Meatbot]

Forgive me if this is a noob question. I know there are no perfectly rigid bodies so that if you had a light-year long rod and pushed it, the other end would not move immediately because if it could, then information could be transmitted FTL.

But, what if you pushed on a quark in the same manner? Would it get compressed as well for a brief moment since it would take time for the movement to reach the other side of it? I would suppose quarks can't be rigid either and it must get compressed somehow. How can you compress a quark though?

 

[Mentz114]

Going down to the quark level is too extreme. When a solid is compressed, the atoms that make it up are not compressed, they just get closer together.

 

[Danger]

Going down to the quark level is too extreme. When a solid is compressed, the atoms that make it up are not compressed, they just get closer together.

There is a caveat to that under extreme conditions. While this is correct for normal pressure, the gravity of a neutron star does in fact compress the electron orbitals into the nucleus. Protons and electrons merge to form neutrons, and some theories suggest that there might in fact be a 'soup' of free quarks in the centre. That's out of my area, though, so someone like Space Tiger would have to sort it out.

 

[Meatbot]

Going down to the quark level is too extreme. When a solid is compressed, the atoms that make it up are not compressed, they just get closer together.

Yeah...I knew that part actually. Sorry I was imprecise. But if no compression can take place in a quark and there are no quark constituents that can get closer, then it would seem you could transmit information FTL over the diameter of the quark. That can't be right though. Or am I thinking of a quark in too much of a classical way?

 

[Danger]

Or am I thinking of a quark in too much of a classical way?

I suspect that to be the case. While I'm neither a particle physicist nor an astrophysicist, I've done a bit of reading in both subjects (ie: I know nothing). It seems to me that since a quark (which can't normally exist in isolation) is so much smaller than a quantum of whatever information-carrying bosun you choose, the question is irrelevant. Again, though, wait for an expert to answer it.

 

[Mentz114]

Hi Meatbot,

... then it would seem you could transmit information FTL over the diameter of the quark. That can't be right though. Or am I thinking of a quark in too much of a classical way?

Quarks don't exist independently at our temperatures but are bound inside nuclei, and so cannot be 'pushed' in the normal sense. I understand your question, and probably nature has arranged that this kind of FTL transmission is impossible.

 

[vanesch]

Would it get compressed as well for a brief moment since it would take time for the movement to reach the other side of it? I would suppose quarks can't be rigid either and it must get compressed somehow. How can you compress a quark though?

In QFT, quarks are strict point particles. Or better, the bookkeeping of strict point particles like quarks, together with requirements from special relativity, give rise to the existence of quantum fields. So when considering them as strict points, it is going to be difficult to compress them. However, if ever it turns out that quarks are bound states of more fundamental things, then they become structures such as atoms, and sufficient pressure will then probably result in a change in the structure of this bound state (such as sufficient pressure can change the binding distance between atoms in a crystal for instance).

So, or quarks are fundamental point particles (as is assumed in QCD), and then you cannot "compress" them, or they are bound structures (such as in technicolor for instance), and then of course you can change their structure, but this will have a dynamics, which will respect special relativity, just like in our steel rod.

 

[tiny-tim]

But if no compression can take place in a quark and there are no quark constituents that can get closer, then it would seem you could transmit information FTL over the diameter of the quark.
That can't be right though. Or am I thinking of a quark in too much of a classical way?

I would suppose quarks can't be rigid either and it must get compressed somehow. How can you compress a quark though?

Your question would be exactly the same for an electron - electrons and quarks are both indivisible particles (erm … so far as we know!).

And we know how to deal with individual electrons, while individual quarks don't seem to exist (so far as we know, they can only come in pairs or threes).

Electrons are normally considered to be point particles with no diameter (or waves!), so there's nothing to compress, and no distance to transmit information.