# Is there a perfect vacuum between atoms in space?

1. Jul 28, 2010

### saln1

As the title states, if I go to space and detect several atoms per square meter of space, does this suggest that the space between these atoms is essentially void of all forms of matter? Thus is this a perfect vacuum?

2. Jul 28, 2010

Staff Emeritus
Yes.

Of course the same thing is true on earth - the space between atoms in the atmosphere is also vacuum.

3. Jul 28, 2010

### saln1

So when I was told a perfect vacuum is impossible, I was told a lie?

4. Jul 28, 2010

### johng23

There is no perfect vacuum because you can't obtain zero pressure. Pressure is a macroscopic quantity of course, it doesn't make sense to say that there is zero pressure between atoms. If you measure the pressure in space, it will not be zero because there are atoms present. If you specify a certain region and try to isolate it in some way while all the atoms are elsewhere, you can't do that...

5. Jul 28, 2010

### fatra2

Hi there,

More or less. You have perfect vacuum at microscopic distance.

However, it is very hard, if not impossible to have a perfect vacuum of long distance.

That's it.

cheers

6. Jul 28, 2010

### DaveC426913

The way we make vacuum on Earth is ostensibly to suck all the air out of a vessel. This is a misrepresentation. There is no such thing as suction.

What really happens is that the internal pressure of the vessel is caused by gaseous atoms bouncing around. When we open the valve and turn on the pump, most of those atoms (because they are bouncing off the walls and off each other) will ultimately fly up the tube and out.

Eventually though, the vessel will reach a very low pressure. The atoms are free to bounce around inside the vessel but they are no longer bouncing off each other. There is no reason why they will fly up the tube except by chance and patience.

The upshot is that you can never get those last few atoms out. The atoms per cubic metre will drop towards zero but never reach it in any reasonable time frame.

7. Jul 30, 2010

### JDługosz

So chill the walls. Next "bounce", the atom becomes frost.

Or, start with a solid with no gap, and introduce a gap by moving parts away from each other. This can be done easily with mercury, for example.

There are other ways of producing vacuum that don't have the same specific limitations.

8. Jul 30, 2010

### Dr Lots-o'watts

Don't forget the constant flow of neutrons everywhere!

And randomly flying free electrons!

And muons!

And them virtual matter-antimetter pairs that spontaneously create themselves out of gamma rays and can cause Hawking radiation if they happen to appear at the event horizon of a black hole!

And more!...

There in no complete vaccum. But these examples, while matter, don't necessarily interact with atoms, so we can often overlook them.

9. Aug 2, 2010

### fatra2

Hi there,

Alright, but what about all the space between the flowing neutrons, electrons, muons, and neutrinos. There is still a great amount of space left, and therefore, empty space left.

Cheers

10. Aug 2, 2010

### felure

11. Aug 2, 2010

### D H

Staff Emeritus

12. Aug 2, 2010

### ACPower

Even when there are no particles in a space, there is still the chance that a 'vacuum fluctuation' will cause a particle and anti-particle pair to emerge spontaneously, with only one of them being in the volume under consideration.

13. Aug 2, 2010

### DaveC426913

"The atom becomes frost??" I know you're playing fast & loose with physics here, so I'll roll with it, but how does a slower moving atom result in vacuum?

14. Aug 2, 2010

### Dr Lots-o'watts

15. Aug 2, 2010

### cragar

we would also have the energy from the G field . And also i can't think of a place in space that you couldn't see a star . all tho their might be one .

16. Aug 2, 2010

### DaveC426913

What does this have to do with the question being asked???

Oh, I got it now. Your comment presumes that the volume of interest need be energy-free.

No, a vacuum does not need to be free of energy; it need only be free of matter.

17. Aug 2, 2010

I've been following this and I thought I was clear on the answer until I got to thinking...

What about the space in between virtual particles? I understand that they don't have a fixed position. I mean is there such a thing as a space so small it precludes the existence of virtual particles?

18. Aug 3, 2010

### JDługosz

No. See Casimir's force.

19. Aug 3, 2010

The Casimir effect is an energy effect. As mentioned earlier in this thread, a vacuum need not be devoid of energy, only matter. The Casimir effect, as I understand it, requires the presence of matter to be observed.

I'm considering a volume of spacetime that is too small for a virtual particle to "pop" into. If the Casimir effect forbids such a small volume from existing, could you please explain to me why. Thanks!

20. Aug 8, 2010

### Acut

Don't forget there's empty space between the nucleus and the electrosphere too.
One of the most puzzling questions I've ever been asked was "According to Rutherford, atoms are big empty spaces. So even a wall is, mostly, space. Why can't we cross it?"

I think when someone who isn't a specialist talks about vacuum, he means "an empty macroscopically-sized space". If we stick to this meaning, then the perfect vacuum only exists between interstellar space - if, of course, it is not disturbed by all the particles previous posters have listed.

21. Aug 8, 2010

### macrylinda

Don't forget the constant flow of neutrons everywhere!

And randomly flying free electrons!

And muons!

And them virtual matter-antimetter pairs that spontaneously create themselves out of gamma rays and can cause Hawking radiation if they happen to appear at the event horizon of a black hole!

And more!...

There in no complete vaccum. But these examples, while matter, don't necessarily interact with atoms, so we can often overlook them.

__________________
watch free movies online

22. Aug 8, 2010

### Xtensity

There is never an empty vacuum because there exist elementary particles which are so small they can pass straight through any walls creating that vacuum.

23. Aug 15, 2010

### DaveC426913

OK, couple of things.

Your 'don't forget' caveats are tantamount to suggesting it is impossible to completely empty a room of people, since there will always be people randomly walking into the room. Well, no. We don't have to count that...

Unless you live inside a nuclear reactor, you shouldn' bre encountering too many flying neutrons...

Or did you mean neutrinos?

Beta radiation? Geez, I hope not.

24. Aug 15, 2010

### Jimmy Snyder

If I'm not mistaken, QFT postulates that particles are points and take up no space. So I don't think there is a volume of space so small that a particle couldn't be there. Quantum physics dissuades us from speaking of things we can't measure. Since you can't measure the number of virtual particles in a small volume of space, you aren't supposed to express knowledge of it. That is, you can't say whether there is a vacuum or not. Did I get that right, or am I missing something?

25. Aug 15, 2010

### cragar

This is probably wrong so please correct me. Could we argue that the energy in a gravitational field is mass in a different form .