Is there such a thing as "empty space? What is the temperature (if any) of "empty space"?

1.In the physical world is there such a thing as “nothing” (“empty space”)?
A vacuum is filled with virtual particles. But is there empty space between these virtual particles? Or does the term lose meaning at this level because even “the space between virtual particles” is filled with greater than zero probabilities of particles being there.

  1. If heat is molecular motion, does this mean that a vacuum has a temperature
    of absolute zero? Or is it meaningless to speak of the temperature of empty space because if there is no molecular action there is no temperature?

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General Questions Moderator

You can’t talk about the space between virtual particles, because you can’t even say where virtual particles are (heck, it’s tough enough just talking about the location of real particles). The potential for the virtual particles is everywhere.

Heat and temperature are two different things. Heat is energy (properly speaking, a transfer of energy). Deep space has almost no energy, because there’s almost nothing to hold energy. Anywhere in the Universe, though, there is at least some microwave-range light, which does have a little energy.

Temperature is defined in terms of what will allow flow of heat. If two things are in a situation where heat could flow between them, but on net it doesn’t, then they’re at the same temperature. If one of those two things happens to be a thermometer, then you can measure what that temperature is. If you put a thermometer in deep space, and the thermometer was at a temperature of greater than 2.7 K, then the thermometer would gradually lose heat to its surroundings. If the thermometer is at a temperature of less than 2.7 K, then it would gradually gain heat from its surroundings. If it’s at 2.7 K, then it will remain at that temperature, and neither gain nor lose heat on net. Thus, we can say that deep space has a temperature of 2.7 K.

Since no new threads have been opened recently, I am reopening this one.

General Questions Moderator

Agree fully, however thermodynamics places no limit on the TIME two things will take to reach equilibrium temperature.

So for example, the earth’s thermosphere is very hot (300 to 500 F), but you can freeze to death (assuming you are well protected otherwise from the vacuum :grinning: and radiation)

The classic Ideal gas equation is PV=nRT

You can rearrange it to P = (Rho) RT. Where (Rho) is density. Rearranging again

T = P / [(Rho) R]

When P gets small and Rho gets small (like the thermosphere), the ratio of the two maybe high but the net unit heat content of a volume is too low.

Typically, a thermometer is assumed to be a massless (actually zero thermal mass capacity) device or its mass is negligible compared to the system being measured. This is not the case, once you start measuring temperature in low density situations. Furthermore - heat transfer (by conduction and convection) is vastly reduced in low density environments. Radiation heat transfer is slow until about a 1000 F. So although the temperature law is still valid, it may take days or years for a thermometer to come in equilibrium with the environment.

It’s always a challenge to measure Temperature in such situations and temperature in these situations is not really of much significance.

I don’t believe scientists have been able to find a “nothing”, or any place in the physical universe where it could be located.

‘Empty Space’ is commonly used to refer to parts of the universe containing no significant mass (no stars, planets, planetoids, etc.). But such ‘empty space’ is full of electromagnetic energy (light, radio waves) passing through it, and seems to have gravity working within it, from what we’ve observed. So it’s not really ‘empty’.

In fact, most of the current recognized theories of physics (quantum mechanics, string theory, etc.) don’t seem to have any way to allow for a ‘nothing’ to exist within the universe.

I believe there’s problems with the 3rd Law of Thermodynamics here as well … something about it being impossible for space to be 0 K … thus impossible for a true vacuum to exist … perhaps someone could explain this better …

Vague memories from physics class half a century ago:
When things get cold, they shrink. The colder they get, the more they shrink. But at absolute zero temperature, they will have shrunk so far that they don’t exist anymore?! But how is that possible?

And the Law of Conservation of Mass/Energy says that Mass/Energy can neither be created nor destroyed (just converted into different forms). So how can something shrink into non-existence?

So this gets into one one of those boundary conditions (like what happens if you go faster than the speed of light? what was there before the big bang?) that science hasn’t yet found an answer to. Not even sure if the question makes any sense.

No, that’s not right. Water, for instance, expands as it cools and forms ice.

Heat is just the movement of particles. As things get colder (lose heat), the particles that make it up slow down. If it’s a gas, they literally stop bumping around so much. If a solid, the particles don’t “vibrate” about their normal positions so much. At absolute zero, all movement would (theoretically, in classical mechanics) stop, but things would not shrink out of existence. Quantum mechanics tells us that reaching a state of absolutely no movement is not possible.

Gases have a volume proportional to their temperature (at least, for any given number of particles and pressure), but that doesn’t mean that they reach zero size at absolute zero: It just means that at some temperature above absolute zero, they cease to be gases.

Most liquids and solids shrink as temperature decreases, but not nearly as much as gases, and only down to some nonzero minimum size.

Other states of matter might or might not change size with temperature, but regardless, none of them will approach zero size as temperature approaches zero.

One thing worth noting is that when it comes to the fundamental building blocks of the world, we might as well just say: “we don’t know.”

There was a time when we thought atoms were the fundamental (atom meaning indivisible) building blocks of the universe. Then we learned of particles making up the atoms. Then of quarks making up the particles.

We can actually observe down to a resolution of about 10-20 meters in particle collisions. The smallest size that we think matter can exist is the Planck length: 10-35 meters, or about 15 orders of magnitude smaller - for scale, this would be as though the smallest object your eye could see was the entire solar system.

It’s possible there is a “nothing” at the smallest scale, or it’s possible that spacetime is like a literal fabric all the way down to that level and “nothing” isn’t a meaningful concept. We just don’t know.

So far as anyone can tell, quarks and electrons are still fundamental. The Planck scale is only relevant to anything in wild guesses.

As far as we can tell, yes. And the Planck scale is an estimate, yes, but the smallest scale certainly isn’t what we observe but at a minimum several magnitudes smaller.

My point was we have no way of being certain if there is or isn’t “nothing” because we can’t even be sure we have the fundamentals of matter licked. We aren’t able to observe matter at the smallest scales, so we can’t say one way or the other.

We don’t even know if there is such a thing as a smallest scale. If you just mean “smallest scale at which there’s any interesting structure”, it may well be the quarks, and there’s no basis on which anyone can say otherwise.

I can routinely see finer than that with my naked eye! :smiley:

No - current physics deals fairly well with temperatures near absolute zero, and there is no prediction - or observation - that matter disappears or shrinks to tiny dimensions.

The lowest temperatures achieved in labs are apparently no more than a few thousandths of a Kelvin above absolute zero.