# Perfectly Rigid Bodies and Quarks

• Meatbot
In summary, quarks can't be compressed, and transmitting information FTL over their diameter is impossible.
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?

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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.

Mentz114 said:
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.

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Mentz114 said:
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?

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Meatbot said:
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.

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.

Meatbot said:
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.

Meatbot said:
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.

## What are perfectly rigid bodies?

Perfectly rigid bodies are theoretical objects that do not deform under any external forces. They are often used in physics problems as simplifications of real-world objects.

## How are quarks related to rigid bodies?

Quarks are subatomic particles that make up protons and neutrons, which are found in the nucleus of an atom. These particles are believed to be the fundamental building blocks of matter and are responsible for the rigidity of objects at a microscopic level.

## Do perfectly rigid bodies exist in the real world?

No, perfectly rigid bodies are purely theoretical and do not exist in the real world. All objects in the universe are subject to some degree of deformation when external forces are applied.

## Can rigid bodies be described using classical mechanics?

Yes, rigid bodies can be described using classical mechanics, which is a branch of physics that deals with the motion of objects and the forces acting upon them. However, at the microscopic level, quantum mechanics may be necessary to fully understand and describe the behavior of rigid bodies.

## What are the practical applications of studying rigid bodies and quarks?

Studying rigid bodies and quarks has many practical applications, such as in engineering and materials science, where understanding the behavior of objects under different forces is essential. In addition, research on quarks and their interactions can lead to a better understanding of the fundamental laws of nature and potentially lead to technological advancements in the future.

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