Come on, yet another type of matter?

[steevey]

How does it have zero thermal energy if its not at absolute zero? It's not at absolute zero, just above it, so it should still have thermal energy right? The atoms should still be moving somewhat. Also, if all the atoms did have the same value of thermal energy which was 0, they should all be in the same lowest energy state, so why isn't it displaying properties of Bose-Einstein condensation or really any quantum mechanical properties?

 

Also instead of getting warmer, it just rises, but couldn't an explanation for that be a simple property of phase change? Super-fluid is as close to a solid that helium will get, but if you can remember, when doing things like melting ice, the temperature of the ice doesn't change because energy has to first be put into changing its phase to a liquid, it should be a similar property of helium when its trying to go to a higher energy state which likes to take up more space.

Edited March 29, 2011 by steevey

[swansont]

He's talking about internal energy (i.e. heat capacity), not temperature. It is exhibiting properties of a Bose-Einstein condensate, though only some of the atoms in the system have condnsed. For He, the deBroglie wavelength at 2K is about a nanometer.

[steevey]

He's talking about internal energy (i.e. heat capacity), not temperature. It is exhibiting properties of a Bose-Einstein condensate, though only some of the atoms in the system have condnsed. For He, the deBroglie wavelength at 2K is about a nanometer.

 

So they are saying it can't be heated up?

Edited March 29, 2011 by steevey

[Fuzzwood]

If it has 0 heat capacity, then yes. Compare it to a perfect black surface in the sun. It releases heat as fast as it gains it.

[swansont]

So they are saying it can't be heated up?

 

No, that's not what he said.

 

 

Any increase in energy means it would not be in the ground state of the system anymore, and therefore not a condensate and not a superfluid. There is a step change in the amount of energy you add or remove and the temperature when you go from a zero heat capacity to a nonzero heat capacity.

[steevey]

No, that's not what he said.

 

 

Any increase in energy means it would not be in the ground state of the system anymore, and therefore not a condensate and not a superfluid. There is a step change in the amount of energy you add or remove and the temperature when you go from a zero heat capacity to a nonzero heat capacity.

 

He's saying it has no thermal energy, but I don't see how atoms can have 0 energy to move themselves. Also if that's true, if it formed an equilibrium with another substance, shouldn't exactly half the temperature be the consequence?

Edited March 30, 2011 by steevey

[swansont]

He's saying it has no thermal energy, but I don't see how atoms can have 0 energy to move themselves. Also if that's true, if it formed an equilibrium with another substance, shouldn't exactly half the temperature be the consequence?

 

He explains what he means by that: it has no internal energy.

[steevey]

He explains what he means by that: it has no internal energy.

 

So if it has no internal energy regarding kinetic energy, if I wrote an equation for a particles wave which contained 0 energy, wouldn't there be no wave?

 

Or better yet, what does it mean by "internal energy"?

[swansont]

Kinetic energy is not internal energy. Internal energy is energy stored in the system, e.g. in a molecule it's in rotational and vibrational modes. In a liquid it would also be in inter-atomic/molecular bonds, such as the attraction that gives rise to heat capacity and the heat of vaporization we see in water. But in a superfluid these forces do not exist anymore, so there is no way to store/extract energy.

[steevey]

Kinetic energy is not internal energy. Internal energy is energy stored in the system, e.g. in a molecule it's in rotational and vibrational modes. In a liquid it would also be in inter-atomic/molecular bonds, such as the attraction that gives rise to heat capacity and the heat of vaporization we see in water. But in a superfluid these forces do not exist anymore, so there is no way to store/extract energy.

 

I thought scientists couldn't say at all that particles moved in any classical sense...Also, why would the temperature effect the actual electro-magnetic fields of particles that causes attraction?

[swansont]

I thought scientists couldn't say at all that particles moved in any classical sense...Also, why would the temperature effect the actual electro-magnetic fields of particles that causes attraction?

 

I made no claims about the motion or the the fields. I said there is energy stored in some states and that the interaction disappears. The atoms in question have condensed into their ground state, so there's no place to store the energy. It doesn't follow a classical model because it's a quantum-mechanical effect.

[steevey]

I made no claims about the motion or the the fields. I said there is energy stored in some states and that the interaction disappears. The atoms in question have condensed into their ground state, so there's no place to store the energy. It doesn't follow a classical model because it's a quantum-mechanical effect.

 

But doesn't the ground state itself have an amount of energy?

 

Or would it be frictionless because it doesn't try to bond with a single thing?

[swansont]

But doesn't the ground state itself have an amount of energy?

 

Or would it be frictionless because it doesn't try to bond with a single thing?

 

The ground state has energy, but cannot store additional energy — that requires a particle being in an excited state.

[steevey]

The ground state has energy, but cannot store additional energy — that requires a particle being in an excited state.

 

What about hydrogen? Isn't it diatonic?

[swansont]

What about hydrogen? Isn't it diatonic?

 

Hydrogen isn't the material that's a superfluid.

[steevey]

Hydrogen isn't the material that's a superfluid.

 

But you were saying the ground state doesn't have enough energy to store bonds, but then why is pure hydrogen diatonic (with the exception of it becoming a plasma) at whatever the temperature? Even if you have super cool liquid hydrogen, its still diatonic.

[swansont]

But you were saying the ground state doesn't have enough energy to store bonds, but then why is pure hydrogen diatonic (with the exception of it becoming a plasma) at whatever the temperature? Even if you have super cool liquid hydrogen, its still diatonic.

 

You mean diatomic, right? Hydrogen forms bonds easily. Helium doesn't.

 

Hydrogen doesn't become a superfluid. I don't know why the subject switched to hydrogen all of the sudden. It's a very different description of the system than for Helium.

[steevey]

You mean diatomic, right? Hydrogen forms bonds easily. Helium doesn't.

 

Hydrogen doesn't become a superfluid. I don't know why the subject switched to hydrogen all of the sudden. It's a very different description of the system than for Helium.

 

 

In both hydrogen and helium, when left alone, the electrons are generally located at the lowest energy level. You said electrons can't hold energy for bonds because they are at the lowest level even though thats where electrons are in hydrogen.

Edited April 3, 2011 by steevey

[swansont]

In both hydrogen and helium, when left alone, the electrons are generally located at the lowest energy level. You said electrons can't hold energy for bonds because they are at the lowest level even though thats where electrons are in hydrogen.

 

No, I never mentioned electron states. These are energy states of a confined system, like a particle in a box or harmonic oscillator.

[steevey]

No, I never mentioned electron states. These are energy states of a confined system, like a particle in a box or harmonic oscillator.

 

But how does a proton have a ground state?

[swansont]

But how does a proton have a ground state?

 

 

We're talking about a bunch of helium atoms, but if you put any particle in a confining potential you will get quantized energy states.

[steevey]

We're talking about a bunch of helium atoms, but if you put any particle in a confining potential you will get quantized energy states.

 

Ok, so then how can an entire helium atom be in the ground state? Isn't it just the electrons that would be?

[swansont]

Ok, so then how can an entire helium atom be in the ground state? Isn't it just the electrons that would be?

 

Now that you have introduced atomic levels as well, you have to specify which ground state you mean. Being in the atomic ground state is the usual condition for an atom. Being in the superfluid/condensate ground state means shedding excess kinetic energy. It has to be the entire atom since it's the center-of-mass motion.

[steevey]

OK, so the atoms are all i their lowest possible state and they're all huddled together, so if I shine gamma-rays on liquid helium, what happens? Wave functions can overlap, so why wouldn't the atoms go to a higher energy state?

[swansont]

OK, so the atoms are all i their lowest possible state and they're all huddled together, so if I shine gamma-rays on liquid helium, what happens? Wave functions can overlap, so why wouldn't the atoms go to a higher energy state?

 

You get what happens in the video.