# Exploring Superfluids: Physical Explanation and Properties at Zero Kelvin

• Entanglement
In summary: Actually, if you measure the pressure and volume of a liquid or gas at a given temperature, you'll find they're not always zero. Pressure and volume always decrease as the temperature decreases, but they never reach zero.That's because the particles in a gas are constantly jostling each other, pushing and pulling on each other. This pushes and pulls on the gas molecules, and it creates a small amount of pressure and volume. But it's never enough to make the pressure and volume equal to zero.But If we are talking about ideal gases PV=nRT at zero kelvin, volume and pressure becomes zero which is impossible as it is a violation to conversation of mass.
Entanglement
Some fluid act weirdly at zero kelvin like Helium

1- it loses viscosity
2- flows upwards along the wall against gravity !

And there is a property I'm not sure about, that it can't be held in a container because it leaks out of it.

However what's the physical explanation for all of that what really happens to the fluid at zero kelvin at the atomic level to make it lose viscosity and move against gravity, and what makes some substance capable of being superfluids while other incapable,I would be grateful to a detailed easy explanation for a high school student, thanks in advance.

1st: The fluid is NOT at zero Kelvin. It is at a low temperature above zero Kelvin. Zero Kelvin is unachievable according to the 3rd law of thermodynamics.

2nd: There isn't much of the actual explanation of that phenomenon that is accessible to a high school student. At those low temperatures a sizable fraction of the Helium gas molecules form a Bose-Einstein condensate which is a state where the molecules share a single quantum state. All the molecules become entangled with each other leading to a coordinated macroscopic behavior which eliminates viscosity (because viscosity relies on molecules randomly interacting with each other, spreading their energy around, and dissipating the flow. That doesn't happen when the atoms behave in a coordinated way due to their quantum entanglement).

dauto said:
1st: The fluid is NOT at zero Kelvin. It is at a low temperature above zero Kelvin. Zero Kelvin is unachievable according to the 3rd law of thermodynamics.
Thanks very much! pressure and volume would vanish at zero kelvin violating law of conservation of mass, so it's impossible as you said.

dauto said:
2nd: There isn't much of the actual explanation of that phenomenon that is accessible to a high school student. At those low temperatures a sizable fraction of the Helium gas molecules form a Bose-Einstein condensate which is a state where the molecules share a single quantum state. All the molecules become entangled with each other leading to a coordinated macroscopic behavior which eliminates viscosity (because viscosity relies on molecules randomly interacting with each other, spreading their energy around, and dissipating the flow. That doesn't happen when the atoms behave in a coordinated way due to their quantum entanglement).
I slightly understand that due to my physics experience as a high schooler, yet I appreciate your help what I want to know is what makes it move against gravity along the sides of the container how is that related to its zero viscosity ?

And why gases never solidify even at temperatures very near to zero kelvin ??

ElmorshedyDr said:
And why gases never solidify even at temperatures very near to zero kelvin ??

Gases do freeze solid if you cool them enough and if the pressure is high enough - you can buy chunks of frozen carbon dioxide at some grocery stores where I live. Helium is unusual in that under a pressure of one atmosphere it won't freeze solid at any temperature.

ElmorshedyDr said:
Some fluid act weirdly at zero kelvin like Helium

2- flows upwards along the wall against gravity !

And there is a property I'm not sure about, that it can't be held in a container because it leaks out of it.
It only flows upwards some centimeters. Hence it can also be kept in a container if the walls are higher than that.
Actually, flowing upwards is not uncommon for ordinary liquids, like water, too. Observe some red wine in the glass next time you drink one on my health!
So if the rim of a wine glass is low enough, it will also leak out.
The only difference to liquid helium is that in liquid helium, there is no surface contact effect involved.

ElmorshedyDr said:
Thanks very much! pressure and volume would vanish at zero kelvin violating law of conservation of mass, so it's impossible as you said.

No, this argument rules out only ideal gas behaviour at zero kelvin.

ElmorshedyDr said:
Thanks very much! pressure and volume would vanish at zero kelvin violating law of conservation of mass, so it's impossible as you said.

No, the 3rd law of Thermodynamics has nothing to do with mass conservation. The law simply states that 0 K cannot be achieved in a finite number of steps. It doesn't claim it violates any physical principle such as mass conservation - that's nonsense.

dauto said:
No, the 3rd law of Thermodynamics has nothing to do with mass conservation. The law simply states that 0 K cannot be achieved in a finite number of steps. It doesn't claim it violates any physical principle such as mass conservation - that's nonsense.
But If we are talking about ideal gases PV=nRT at zero kelvin, volume and pressure becomes zero which is impossible as it is a violation to conversation of mass. But since there is no such thing called ideal gas, that isn't true, then why non-ideal gases can't achieve zero kelvin

Again, you're being careless in your logic steps. The mass of the gas is proportional to n, not V. Also, T=0 does not imply that "volume and pressure becomes zero". It implies that volume OR pressure become zero, so there is a perfectly good solution with finite volume and density and zero pressure and temperature.
The 3rd law doesn't say that the zero K state is meaningless. It states that it is unachievable through a finite number of thermodynamic processes.

DrDu said:
No, this argument rules out only ideal gas behaviour at zero kelvin.

Not even that. The argument is just plain wrong.

ElmorshedyDr said:
But since there is no such thing called ideal gas, that isn't true, then why non-ideal gases can't achieve zero kelvin

The laws of thermodynamics, including the third law, apply to all gases, whether ideal or not. And the third law says that you cannot cool anything down to absolute zero.

Nugatory said:
The laws of thermodynamics, including the third law, apply to all gases, whether ideal or not. And the third law says that you cannot cool anything down to absolute zero.
Why??

Ok ok guys, I'm still a freshman at physics,
What I know is that PV = nRT is only for ideal gases, let's make an well organized conversation so I don't get confused, If we suppose that ideal gases exist why couldn't it reach to zero kelvin ??

ElmorshedyDr said:
Why??

It's a law. If there was a why it would be a theorem.

There are justifications for if from the point of view of statistical mechanics but for now you probably ought to concentrate on understanding it from the point of view of thermodynamics.

ElmorshedyDr said:
Ok ok guys, I'm still a freshman at physics,
What I know is that PV = nRT is only for ideal gases, let's make an well organized conversation so I don't get confused, If we suppose that ideal gases exist why couldn't it reach to zero kelvin ??

there are two ways you can use to remove energy from an ideal gas

1) Heat: You would have to find something colder than the gas to absorb the heat given off by the gas. Nothing can be at zero Kelvin or below so that wouldn't work.

2)Work: The capacity of the gas to perform work as it expands is proportional to its pressure that also decreases as the temperature drops so that doesn't work either.

You're out of luck.

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ElmorshedyDr said:
Ok ok guys, I'm still a freshman at physics,
What I know is that PV = nRT is only for ideal gases, let's make an well organized conversation so I don't get confused, If we suppose that ideal gases exist why couldn't it reach to zero kelvin ??

Loosely speaking, an ideal gas is one which the variation in the amount of energy carried by a single particle is small compared with the total amount of energy contained in the volume of gas. As you cool the gas towards absolute zero, the total amount of energy contained in the gas becomes smaller while the particles stay the same size, so eventually the ideal gas assumption breaks down. Thus, any real gas will stop behaving like an ideal gas if you cool it enough - or equivalently, ideal gases only exist if you stay away from zero kelvin.

And as for your other question, why an non-ideal gas (or anything else, for that matter) cannot reach zero kelvin...

Well, how would I cool something down to zero kelvin? I'd put it in contact with something colder, and let heat flow from my object into the colder object (a heat sink), thereby reducing the temperature of my object. But that heat flow will warm the colder object, so even if it started at zero kelvin, it won't stay there and my two objects will reach equilibrium at a temperature somewhere slightly warmer than zero kelvin. Now, you may object that we just have to cool the heat sink back down to zero kelvin again - but that's exactly what we're trying to do with the first object, so we've just moved the problem around.

## 1. What is a superfluid and how is it different from a regular fluid?

A superfluid is a state of matter that exhibits zero viscosity, meaning it has no resistance to flow. It also has other unique properties such as the ability to flow without any loss of kinetic energy. This is in contrast to regular fluids, which have some level of viscosity and will experience energy loss when flowing.

## 2. How is the concept of superfluidity related to the concept of superconductivity?

Both superfluidity and superconductivity are related to the phenomenon of quantum mechanics. Superconductivity is the property of certain materials to conduct electricity with zero electrical resistance. Similarly, superfluidity is the ability of certain liquids to flow without any resistance. Both of these properties are a result of the particles in the material being in a state of quantum coherence.

## 3. How is superfluidity observed and measured in experiments?

Superfluidity can be observed through various experiments, such as the Helium-4 experiment where the liquid is cooled to near absolute zero and then allowed to flow through a small hole. The flow rate through the hole will be constant and independent of pressure, demonstrating superfluidity. Other methods of measurement include studying the rotation of a container of superfluid and measuring changes in temperature and pressure.

## 4. What are the main applications of superfluids?

Superfluids have a range of potential applications in various fields, including cryogenics, quantum computing, and medical imaging. For example, superfluid helium is used in cryogenics to cool materials to extremely low temperatures. Superfluid helium is also used in MRI machines for medical imaging due to its ability to remain in a liquid state at low temperatures.

## 5. What are some current areas of research in the study of superfluids?

Current research in the field of superfluids is focused on understanding the fundamental properties and behavior of these unique materials. Scientists are also exploring new methods for creating and manipulating superfluids, as well as potential applications in areas such as energy storage and transport. Additionally, there is ongoing research into the connection between superfluidity and other phenomena in quantum mechanics, such as Bose-Einstein condensates.

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