Hey Quantum,

What is the speed of sound at Absolute Zero? Or, is there sound in a closed system with a temperature of Absolute Zero?

Jim

I don't think you can have sound at absolute zero, because the act of injecting sound energy would raise the temperature above absolute zero. The reason sound doesn't propagate forever is that acoustical energy is converted into heat.

quantumeffect

The actual heat exchange is achieved through evaporation (at the evaporator coil).
So it is really a delta H of vaporization thing and not a gas phase pressure-volume thing.

Oh, OK. The same process is being used, but they are using it to convert the refrigerant from gas to liquid and back to gas again. They are just using compression and expansion to provide the heating and cooling effect that causes the condensation/evaporation cycle. I guess the use of an endothermic reaction like evaporation makes it more efficient than the raw compression/expansion effect would provide, eh?
 

I always thought that at absolute zero, the protons and electrons in atoms would annihilate one another. Absolute zero = zero kinetic energy. 

if you had big enough sub-woofers you could maybe create a bass trap waffle iron

That's the most quotable observation you've offered up in some time, Dean.

I don’t know the answer to the question about the speed of sound at 0 K but, the answer probably depends upon how you interpret the theoretical absolute zero.

In post # 23 I referred to the specific heat or adiabatic constant (“Y” in Drew’s analysis) as degrees of freedom or the way particles move at the atomic or molecular level.  If at absolute zero, particles are at complete rest then and you have (hypothetically) zero kinetic energy, I suspect (and I am guessing) that the speed of sound approaches zero.

Weird things start to happen at very low temperatures because quantum mechanical effects have to be taken into consideration.  This is a really bad analogy that I use in freshman chem classes and would probably give a serious physicist an aneurism but here goes …

Even if folks don’t do math  …  they at least descriptively, have a grasp of terms like energy and power (even if used incorrectly).  That said, the world we observe is like diving in a car.  You can stop the car and then accelerate to any desired speed (obviously within reason) and you can imagine the vehicle possessing different amounts of energy at different speeds.  Here is the important point, as you accelerate, you gradually and continuously obtain the next speed or in other words, you start at 0 mph and then get to 55 mph and in so doing you go every speed in between …

Now imagine yourself in a world where everyday observations are governed by quantum mechanics.  You would get into your car and it would be going 5 mph … that’s it, you have no choice in the matter, it can’t go 0 mph, the slowest speed is 5 mph.  When you stomp on the accelerator your car instantaneously goes 35 mph without going any speed in between … you step on the accelerator again and you are instantaneously doing 55 mph.  That’s it, you’re either doing 5 mph, 35 mph or 55 mph.   .  When you can only go certain speeds and nothing in between you would say that your speed is “quantized”.  A very strange world indeed and a difficult one to conceptualize.
 
*** NOTE, THE SPEED THING IS AN ANALOGY ... WHEN WE ARE TALKING ABOUT ATOMS, IT IS THE ENERGY THAT IS QUANTIZED ***
 
On the scale of atoms and molecules this is the way the world behaves.  In the quantum mechanical world, when you get to absolute zero, your system will have something called a quantum mechanical zero point energy (or by analogy, that’s when your car is going 5 mph and can’t go 0 mph).

The physics of something called the Bose-Einstein condensate is a really cool (pun intended) area of low temperature research (I don’t think the Bose in Bose-Einstein is the speaker guy).  A Bose-Einstein condensate is a collection of gas particles at a temperature very near absolute zero that are all driving the car at 5 mph.  You can essentially observe the quantum mechanical world in these particles.  Back in 1997 (there is probably more recent research) some dudes at MIT used our tax dollars and sodium atoms to form a Bose-Einstein condensate and measure the speed of sound.  The speeds they reported in their paper depended on the density of the condensate and ranged from 4 to 10 mm/s … that’s millimeters per second.

As an OT note, researchers back in in the 90’s got light down to about 38 mph in Bose-Einstein condensates.  Since then (there is a group at Harvard) researchers have been able to stop light and restart it ... and no, I don't mean with a strobe light and a joint.

If at absolute zero, particles are at complete rest then and you have (hypothetically) zero kinetic energy, I suspect (and I am guessing) that the speed of sound approaches zero.

This makes perfect sense.

I remember watching a documentary on the subject of absolute zero, and someway into the film, they started talking about Bose-Einstein condensates, which can only exist at or very close to A.Z.

We have actually built devices to implement this, and one of the predicted effects was that even the speed of light would be slowed down to a crawl (you could see light itself moving slowly through a prism). With my limited knowledge of physics, it seems only natural that the speed of sound would likeiwse be slowed at very cold temperatures much the same way as light.

 
 Being in the HVAC trade I am constantly  involved with  temparture/pressure charts and how the different gases react to varying changes. It is interesting to see those relationships being applied to sound and its propagation and speed. Maybe I missed something here( very likely) but did you relate the speed of sound to freq and medium traveled through?
  The guys at BBE built a company on the concept that sound travels at different speeds depending on freq.I know Bitflipper will probably say that they use pseudo-science to arrive at that conclusion but I am not convinced of that yet although I am convinced that the BBE isn't a go to thing for everything.

  Freq. and medium have to be a big factor IMO,why else do submarines use ultra low sonar for the medium(the earth and water) they chose? In space which is assumed to be an airless vaccum sound has nothing to travel through correct?

  Bitflipper if you have a mind to improve your bad air circulation drop me a PM and maybe I can help to at least get your space to a constant temperture. That way at least you can have level calculations.lol.

Starise

Freq. and medium have to be a big factor IMO,why else do submarines use ultra low sonar for the medium(the earth and water) they chose?

Most likely because low frequencies are not easily absorbed and thus travel much further.

Bass trap waffle iron!
Bass trap waffle iron!
Bass trap waffle iron!


(Sorry, I read "Zippy the Pinhead" daily in the local newspaper.)

Jimbo21

From this equation: c=(γ*R*T/M)^1/2 , I believe c is the speed of sound. If so, if you plug in 0 degree Kelvin then c= 0. Is that right?

Near absolute zero, air (or anything else) would be solid rather than gas, so those gas equations would not apply.  Gas laws don't apply at extreme (high or low) temperatures anyway.

Sound travelling through solids was touched on earlier in post 28.

Maybe density is not a factor because humans will not be hearing anything at the extremes.

At some point altitude results in no sound and no humans. So at what density of the atmosphere is sound not transmitted?

Wonder what the curve looks like for sound vs temp over a humanely useful range: 343 at 20, 349 at 30,....

Does the speed of sound in water (100% humidity?) change significantly at various depths?
I assume the greater the depth the colder the temp would reduce speed. But what effect does such extreme density have? At what frequencies?


(Absolute Zero: nobody's home.)

J

Actually, they are looking for thermoclines, divisions between temperature layers in the water that reflect sonar signals. You have to be above one if you're listening to surface ships, but you want to be below one if you're hiding. I learned that playing "608 Attack Sub".

I have intentionally not mentioned time travel, Dave, and was hoping no one would bring it up. Now we have to add the gravitational constant to the formula, which greatly complicates things for our forum brethren on Jupiter.

TOO MUCH MOVEMENT WILL MAKE THE BROWN NOTE HAPPEN.