# Absolute zero

In this column, Cecil writes “The colder something gets, the less internal motion or vibration its molecules exhibit. At absolute zero–that is, zero degrees Kelvin or -460 degrees Fahrenheit–molecular motion virtually stops.”

Virtually stops? What continues to move at absolute zero?

I’m having trouble understanding the other end of it. How come particles increase in mass when they speed up? Does my car increase in mass when I speed up?

Yes it does. If your car’s rest mass is m, then at velocity v will be (m/sqrt(1-(v/c)^2)). At 55 mph, a 1000 slug car (32200 lbs in your driveway) would have a mass of approximately 1000.0000000000033646130749485935 slugs which would be just over 0.0000000001 lbs at 1g.

A system at absolute zero temperature still as vacuum energy or zero point energy (depending on whether you want to talk about matter/energy as fields or particles on a given day). Vacuum energy is the energy inherent in the tension of space; you can create an area with a lower energy state and the “vacuum” will fill the void with virtual particles. (This has been demonstrated experimentally; see Casimir Effect.)

Cecil is speaking of the increase in relativistic mass, or more properly, the increase in apparent mass due to the increased momentum of the system. This is a fundamental result of Special Relativity. The increase in mass of your car is immeasurably insignificant, but as you add energy into a system, it does become more “massive”. A very high temperature (relativistic) plasma can have a momentum far larger than the product of its invariant mass and velocity.

Stranger

Cecil wrote, “For comparison, the center of the sun bubbles along at 15 million degrees K (15 x 10^6); silicon can be created by fusion at 1 billion K (10^9). In short, the Planck temperature is very toasty indeed.”

So nothing can be hotter than the Planck temperature. I get it - kind of like Rebecca Romijn: http://www.fashionmodeldirectory.com/models/rebecca_romijn+stamos/showphoto/44802.

I think I just experienced a significant increase in my Planck Distance.

In the Real World you can’t have anything at absolute zero – if all motion stopped, then you’d simultaneously know its position and its momentum, and violate the Uncertainty Principle. So you can approach absolute zero, but not actually get there. You’re going to start descending into Quantum Foam if you start getting really cold and really small, and start seeing the effects Stranger refers to.

The Planck temperature isn’t really the maximum temperature, but more like the largest temperature for which our current understanding of physics is meaningful. The temperature could go higher; we just have no good idea how things would work then.

I’d make that statement a little stronger, even. The Planck temperature is our best guess at the upper limit at which our present understanding is meaningful. The same goes for most of the other Planck quantities: We’re certain that there’s no change in action or angular momentum smaller than [del]h[/del] (the Planck angular momentum), and that there’s no meaningful speed greater than c (the Planck speed), but any other Planck quantity you care to construct, it’s pure guesswork that it represents any sort of absolute limit.

[sub]Everyone’s always looking for a piece of the action, but Planck already found it.[/sub]

I was given some excellent explanations in this thread I started on the subject back when I was a newbie.