Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Lord Antares on 30/07/2016 00:24:01
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So, the definition of a vacuum is ''space devoid of matter'', which is straightforward.
However, to make a claim of a space without matter, you would have to say ''from point A to point B, there is no matter'' (or ''in between these end points there is no matter'' if you consider 3 dimensions).
Scientific papers say that there exists no vacuum in the universe because even in the most desolate parts of the universe there are about 3 atoms in a cubic meter. To me, this makes no sense and I drew this shitty illustration to help explain why: (EDIT: ignore the lack of a dimension here, this was kept basic just to show the point)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F2Tx4o5e.png&hash=946163eae4af7676ec153b3072a31a5f)
The green area (cubic meter) is clearly not vacuum. However, why isn't the blue area a perfect vacuum? Why isn't all the space in between these atoms considered vacuum?
Why would a cubic meter be used to show there is no vacuum since it is not a mathematically relevant unit? (As in, it is not a ''natural'' unit like the planck units)
Why couldn't I, following the same logic, say ''there are no atoms in this cubic centimeter of deep space; therefore, perfect vacuum exists.''?
Isn't then empty space/vacuum just equal to space? Isn't space/vacuum an entity through which particles and waves move and matter an entity off of which the same particles and waves bounce?
Doesn't any place in between matter/atoms possess the same properties as vacuum and why isn't it considered as such then?
I hope someone can clarify this; thanks for your answers in advance.
I am not a physicist or any kind of professional scientist but I wish to learn.
EDIT: I need to copy and paste this from another place where I wrote this for further clarification:
As I said, I'm not a physicist, but simply logically, the definition can't be exact.
Because the logic ''there is no perfect vacuum since there are ~3 atoms in a cubic meter even in the rarest parts of the universe'' is used to prove there is no vacuum, surely the statement ''there exists perfect vacuum since we know there are cubic centimeters in the universe which contain NO atoms'' must be just as valid because it uses the EXACT same logic, which absolutely nothing changed except for the unit of measurement.
You see what I mean? To state that there is or is no vacuum, you would have to state the end points between which are or aren't any particles. So why would you use a cubic meter to determine that? Why not the smallest possible unit you could use?
I guess the point of my statement is that I think it's ridiculous to state that there are no cubic meter-sized vacuums in the universe, because that has no relation to physics since it unnecessarily complicates the issue with scale.
I hope the question makes sense now.
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The quality of a vacuum is a relative thing, and a temporary thing.
Although there may be no atoms in this cubic centimetre in this second, atoms are typically moving very quickly, so there probably will be an atom in that specific cubic centimetre, in the next few seconds or minutes.
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True.
But this would mean that this notion of vacuum is flexible and moves according to the position of the particles.
There is a vast number of cubic centimeters in the universe in this instant which contain no particles, ie. are vacuums. In any given instant in the future, the position and shape of these vacuumed areas would be shifted but the overall volume of these areas combined would be exactly the same, no?
Even if you were to bunch all the particles in the universe at one spot (meaning as close to each other as possible), there would be the same amount of vacuum in the universe, because there will be the same amount of overall particles which occupy space.
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You have drawn the atoms as "points" but actually they are diffuse clouds with no "edge".
There's nowhere in the green box where that atoms don't have at least a small chance of being, so there's nowhere in the box where there's a vacuum.
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This was a very simple drawing just to show the point.
Everything has a chance of being somewhere, but it only in one place at a given time.
So, we can say, that on average, 3 atoms will populate the green box, no matter their position. There will still be empty space between them.
Are you proposing that any space that CAN be populated with matter should be observed as though it is populated with matter, negating this vacuum idea?
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Everything has a chance of being somewhere, but it only in one place at a given time.
I take it you are not familiar with quantum mechanics.
Everything is (at least slightly) everywhere.
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I am not, but as I understand it, ''everything is everywhere'' only means that particles could be in any position due to movement, forces, etc.
Also, given enough time, all spaces or positions within this box will be passed through by atoms.
If this is what you mean, then it is true, but it only means that particles CAN and in time WILL be in any different position. If you look at a point in time, they will still be in a given place and there will be empty space between them. In any future point in time, all the particles will be in different position, but there will still be empty space between them. Any area between any particles is dynamic and changes shape according to movement of those particles.
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Nature abhors a vacuum
The early Greeks philosophers didn't like the idea of a vacuum - nor did they see the need for a zero.
I am happy with the concept of a vacuum, even though it may be a zero which is not quite zero all the time.
The thing that all nearly-vacuums have in common with the thin atmosphere of Mars - if you try to breathe it, you die (quickly!).
See: https://en.wikipedia.org/wiki/Horror_vacui_(physics)
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I am not, but as I understand it, ''everything is everywhere'' only means that particles could be in any position due to movement, forces, etc.
No.
The particles have no "edges". They spread out into space so they are always everywhere.
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Hm, interesting.
If that is the way it is, how would one be able to count the number of particles in anything? How would you be able to say that body x contains more particles (i.e. is more dense) than body y if there are no boundaries or edges of particles? Wouldn't that be one spread-out wave-particle no matter what?
I am not disproving what you are saying, I am just genuinely interested.
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If that is the way it is, how would one be able to count the number of particles in anything? How would you be able to say that body x contains more particles (i.e. is more dense) than body y if there are no boundaries or edges of particles? Wouldn't that be one spread-out wave-particle no matter what?
My understanding is that the scenario described by Bored Chemist exists only when it is not being observed. When being observed particles can be discrete; but as we cannot observe the entire cosmos, what we might identify as empty space might be “inhabited” by spread out particles from elsewhere.
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Strictly, you can't. But you can say something like "there is a better than 99.99% probability that there are between 999 and 1001 particles in this volume of space."
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What is your definition of perfect, vacuum and space?
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Let us also consider that with very few (if any) exceptions, all of space is full of photons (starlight, blackbody radiation from nearby "cold" objects, cosmic background radiation etc.)