If strings are vibrating all the time, then...?

[browndn]

where do these "strings of energies" keep getting their energy from since they they are using energy to vibrate. I dont a lot about strings so this Q might sound naive.

[iNow]

I don't know the answer to your question, but I see a potential problem in your assumptions.

 

Do you have any evidence (again, I don't know) that strings are using energy to vibrate?

[browndn]

Do you have any evidence (again, I don't know) that strings are using energy to vibrate?

 

well i mean, if it is "vibrating" [a form of motion], it needs enrgy right? well i dont have any evidence cuz im just scratching the surface about strings.

[Klaynos]

taking the simplest of possibilities, if it's SHM (simple harmonic motion) it does not require external energy to be added, the total energy of the system remains the same.

[ajb]

Klaynos is on the right lines. All quantum field theory and string theory (non-interacting at least) looks like a collection of harmonic oscillators.

[Riogho]

It also vibrates by nature.

 

You might ask why atoms are constantly oscillating back and forth, but they are, due to the fact that they cannot be at a zero-point because then we would know their position and velocity therefore they MUST be moving.

[bob000555]

That analogy is flawed Riogho atoms vibrate due to thermal energy and indeed at absolute zero they stop vibrating.

[swansont]

That analogy is flawed Riogho atoms vibrate due to thermal energy and indeed at absolute zero they stop vibrating.

 

Except you can't reach absolute zero.

 

Let's take an ensemble of atoms and put them in some kind of confinement, (like a magnetic trap) of characteristic size 1 cm. The zero-point energy for that is of order 10^-21 eV for atomic masses around 100 amu. The equivalent temperature of that is around 10^-17 K.

 

Quantum fluctuations in macroscopic systems are small. Not reaching absolute zero is a classical limitation, that is not contradicted by quantum mechanics, but neither is it driven by QM in classical systems.

 

The oscillations in question — strings — are not thermal-atomic-motion in nature.

[Daecon]

The kinetic energy of the string isn't being dispersed or dissipated in any way. Strings are the most fundamental of particles and are essentially in perpetual motion because the energy in the string can't go anywhere else.

[Riogho]

That analogy is flawed Riogho atoms vibrate due to thermal energy and indeed at absolute zero they stop vibrating.

 

No, it isn't. Vacuum energy says they will never reach absolute zero. And even if IT DID. They would STILL BE MOVING.

 

Or so says feynman. Argue with him if you disagree.

[iNow]

And even if IT DID [atoms reach absolute zero]. They would STILL BE MOVING.

 

This doesn't sound right, as absolute zero is the complete lack of kinetic energy and is not reachable ta boot. Can you source your comment that atoms would still be moving even if they reached absolute zero? It seems very contradictory, and I'd like to read more.

[Riogho]

The following excerpt is from the late physicist Richard P Feynman's book "The Feynman Lectures on Physics" by Feynman, Leighton, and Sands, Addison-Wesley: Menlo Park, CA, 1963

 

 

"As we decrease the temperature , the vibration decreases and decreases until, at absolute zero there is a minimum amount of vibration that the atoms can have, but not zero. "

[iNow]

Thanks for the quote, but I do not think it means what you think it means. Your appeal to authority is great, especially since I am a big fan of ole dick feynman, but when he said,

 

"As we decrease the temperature , the vibration decreases and decreases until, at absolute zero there is a minimum amount of vibration that the atoms can have, but not zero. "

 

... I read that to mean that, "one cannot reach absolute zero," not "atoms will still vibrate when at absolute zero" as you've clearly and intentionally implied with your post above.

 

 

Farm boy, polish my horse's saddle. I want to see my face shining in it by morning.

[swansont]

As I said before, absolute zero from the second law of thermodynamics is a classical concept, before the development of the idea of a quantum-mechanical zero-point energy. Absolute zero was the removal of all center-of-mass kinetic energy of the atoms. The Feynman quote is accounting for the fact that when incorporating QM, you have to say that absolute zero is the removal of all available kinetic energy, and you will have the zero-point amount left. But as I demonstrated earlier, that amount is really small in macro systems.

 

In any event, you can't reach absolute zero, and you can't bring atoms to a complete stop.

 

This also points to the problem of simply quoting authorities on the subject. Feynman was correct, but his statement has to be taken in context in order to be understood, because even though it contradicts iNow's statement in post #11, iNow was also correct, taken in context. It was a comparison of quantum apples with continuous oranges.

[Riogho]

So, what you are saying is it's just wrong.

 

In a classical sense, you reach absolute zero and nothing moves.

 

In a quanticized sense, you cannot reach absolute zero and therefore there is still motion.

 

So I was cross-referencing for my example?

[swansont]

So, what you are saying is it's just wrong.

 

In a classical sense, you reach absolute zero and nothing moves.

 

In a quanticized sense, you cannot reach absolute zero and therefore there is still motion.

 

So I was cross-referencing for my example?

 

Almost.

 

In a classical sense, you can't reach absolute zero, which is where nothing is moving, so there is motion.

 

In a QM sense, you can't reach absolute zero, but this is where there would still be some small amount of residual motion from the zero-point energy.

[Riogho]

Why can't you reach absolute zero in the classical sense? I thought a vacuum was perfectly valid in classical mechanics?

[iNow]

A vacuum [math]\ne[/math] 0 kelvin.

[thedarkshade]

Why can't you reach absolute zero in the classical sense?

A very rough reason would be that you need something colder so you can reach an equal value of temperature with.

[Riogho]

A vacuum [math]\ne[/math] 0 kelvin.

 

>.< I thought a vacuum was the absense of anything. Therefore, it would have no temperature... which is 0 kelvin.

 

...

 

Elaborate for me please?

[iNow]

>.< I thought a vacuum was the absense of anything. Therefore, it would have no temperature... which is 0 kelvin.

 

...

 

Elaborate for me please?

 

You're close, but IIRC it's more that temperature is a property of matter itself, and as you mentioned a vacuum is without matter. These points taken together imply that the concept of temperature is meaningless when matter is not present... it does not follow that a vacuum is "zero K." Additionally, a perfect vacuum is not exactly common.

[swansont]

A classical vacuum has no temperature — there's nothing to measure. Reaching 0 K implies you were originally at some nonzero temperature.

[Riogho]

I thought temperature was a measure of heat. And I thought something couldn't have heat, that heat was only the transfer of energy from one source to another.

 

Therefore, I deduced that no sources = no heat = nothing = vacuum.

 

Oops

[thedarkshade]

Heat represent the rapid shake of molecules but microscopic in distance.

 

Vacuum = no molecules:D

[swansont]

I thought temperature was a measure of heat.

 

Heat represent the rapid shake of molecules but microscopic in distance.

 

No, we've been through this recently. Temperature is a measure of vibrational/rotational energy, but heat is not a property of matter.