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Author Topic: how many of you believe that a vacuum can have temperature?  (Read 5961 times)

Offline abhishek_singh

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as i heard it many times that vacuum persist temperature but i don't agree with this point


 

Offline PmbPhy

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Quote from: abhishek_singh
as i heard it many times that vacuum persist temperature but i don't agree with this point
You'll have to be more precise. What exactly did you hear? Interstellar space is filled with black-body radiation. If you don't know what that is please see
http://en.wikipedia.org/wiki/Black-body_radiation

Space is filled with this kind of radiation. It's called the Cosmic Microwave Background Radiation (CMBR). See
http://en.wikipedia.org/wiki/Black-body_radiation

But space is not a vacuum in the sense that nothing is there since it's filled with photons. It's called 3K radiation. It's said to have a temperature of 3 Kelvin because the radiation coming from it is just like the radiation coming from a body having a temperature of 3 Kelvin.
« Last Edit: 25/06/2014 13:12:48 by PmbPhy »
 

Offline yor_on

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A temperature needs particles (of rest mass), interacting with photons as its 'force carriers'. Virtual particles, or as I prefer to think of it, indeterminism, as well as Hup, may allow for a measurable temperature under some really weird conditions as at a Event horizon possibly?

Temperature is kinetic energy, becomes radiation, comes from rest mass interacting. The rest of it depends on how seriously you take the concept of 'virtual particles'. Heat is another concept discussing how 'energy' transfers from one system/object to another.
« Last Edit: 23/06/2014 11:41:46 by yor_on »
 

Offline yor_on

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The point is that there is nothing stopping a vacuum from being filled with bosons as photons. And you might want to call it 'heat', but there will be no measurable temperature unless you introduce rest mass to interact with it. So without introducing rest mass it becomes a meaningless concept to me. Think of the Big bang, and that moment of radiation, was it a heat, and was it a temperature? Without rest mass existing, interacting? Heat need a transfer as I get it, temperature s defined as kinetic energy of particles.

As I said, how seriously you take the concept of 'virtual particles' will decide the rest.
 

Offline PmbPhy

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Quote from: yor_on
And you might want to call it 'heat', ...
No. You can't do that. By definition heat is flowing energy. If the energy is not flowing then it can't be called heat. In any case he's looking for temperature, not energy. Two bodies with the same energy don't necessarily contain the same thermal energy.

Quote from: yor_on
..but there will be no measurable temperature unless you introduce rest mass to interact with it.
That is incorrect. You need more than something that has rest mass I order to measure temperature. E.g. you can't measure the temperature of the CMR by placing an electron in it and observer how it moves. You have to place a body into the CMBR that can itself have a temperature. I.e. all you have to do to measure the temperature is do the same thing you always do to measure temperature; place a body in the CMBR and wait for it to come to thermodynamic equilibrium with its surroundings. It will then take on the temperature of its surroundings and you then measure the temperature of the body. For example; place a thermometer in the CMBR and look at the temperature reading.
 

Offline yor_on

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What do you mean by 'body' Pete?
=

Ah, any collection of particles interacting, but not one particle. Ok, makes sense, I think ?:) That should mean that you need more than the random movement of one lone particle to create heat. So it is then particles of restmass interacting with each other that creates radiation, but one particle inserted in a field of radiation does not beget a temperature, although there should be a interaction there too?
==

This one was tricky, there are more types of heat than IR that we mostly see describing it. IR 'energy' apparently belong in the transitional region of a molecule and that's why we see it discussed so much in for example global warming. It's discrete energies (photons) and molecules have discrete vibrational quantum states fitting IR.
« Last Edit: 23/06/2014 22:56:39 by yor_on »
 

Offline yor_on

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That should pretty much end any idea of virtual particles having a temperature, shouldn't it? They are allowed because of their assumed 'indefinite existence' (too short to measure, as in prove, all as I get it) so there can be no 'flow' for them either, or can it? On the other tentacle, they are assumed to be force carriers, in which case they must interact somehow?
=

I find it easier imagining it as indeterministic, although obeying certain rules, than believing in a reality of virtual particles myself. Then one could see it as if it was a 'field' that makes it happen, and I don't need to think of it as virtual particles, somehow existing.
« Last Edit: 23/06/2014 23:28:34 by yor_on »
 

Offline yor_on

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So what about the Big bang folks? A lot of 'energy', but no rest mass, or collection of particles. That should mean no heat, if I'm thinking correctly. Can 'energy' create a photon by itself? As if a concentration of energy both create photons (bosons) and matter (fermions)? And if I got Einstein right, also define a SpaceTime with 'dimensions' and all? So where did the boundaries/limits defining this come from?
 

Offline yor_on

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Energy is a property of objects? I think of it as a result of transformations 'coins of exchange' as JP formulated it. Another aspect of it is the theory that energy can't be destroyed. That one is old, going back to around the French revolution as I think, or maybe even older (what about the Greeks, etc?). Anyway, you can only transform as I see it, and there must be objects to measuring this transformation. It's the same enigma as the one I was referring to with heat and temperatures. You need matter for measuring. Whether one particle is, or isn't, enough, as Pete points out? Maybe Pete, but if heat and temperature are properties belonging to rest mass, then why wouldn't they still be properties of a electron, even when unmeasurable?

Properties and constants.
==

Or could you think of it as something similar to decoherence in intent? The way something indeterministic becomes macroscopically deterministic (well, more or less at least :)? As some sort of statistical response to what 'reality' should be? then the threshold here is a 'collection of particles' isn't it? What would it mean? Two particles is enough for a transfer of kinetic energy, isn't it so? Not really the same, is it? Although, it doesn't really matter for it. It's about properties, isn't it?
« Last Edit: 24/06/2014 11:14:02 by yor_on »
 

Offline evan_au

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The solar corona is a pretty good vacuum, when considered by Earth standards. It has a temperature of around 1 to 4 million degrees Kelvin. Due to the very low density, it contains very little heat energy, despite its immense temperature.

If you put your thermometer in the solar corona, its temperature would gradually rise until it was at a temperature of millions of degrees - only it would evaporate into a plasma long before it reached thermal equilibrium. In practise, the temperature of the corona is measured by detecting spectral emissions from highly ionised metals like Iron.

If you want to consider a "perfect" vacuum, with no particles apart from your thermometer, you could put your thermometer in intergalactic space, far from any wandering planets, stars or gas clouds. In this case, the temperature of the thermometer would slowly decline until it approached around 2-3 Kelvin, which represents thermal equilibrium with the Cosmic Microwave Background Radiation.

So I would have to conclude that a vacuum does have a temperature.
 

Offline yor_on

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Only in relation to matter, as I think, Evan. And that one is about how matter (and photons) came to be to me. A photon is a discrete energy packet, the cleanest approach to 'energy' in itself that I know of. It has no dimensions as far as I've read, but we say it has a speed, and so a momentum, also dependent on its 'energy'. I could imagine a universe of photons, but for such a universe to create matter? We measure on the symbiosis of matter and light and we talk about 'regimes' of different temperatures and so 'energy'. Without matter, where is the temperature, and where is the heat?
==

If I would want to think of the Big Bang as a symmetry break instead, then heat and temperatures seems to become something isolated, as in specifically belonging, inside this 'symmetry break' of a universe, is that not so?
« Last Edit: 24/06/2014 11:53:58 by yor_on »
 

Offline burning

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Only in relation to matter, as I think, Evan.

What do you mean by this? Specifically, when you say that vacuum only has a temperature in relation to matter, how do you view that as different than the temperature of any other physical system?
 

Offline PmbPhy

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Quote from: yor_on
What do you mean by 'body' Pete?
Exactly what you'd think it means. A collection of atoms and molecules which are plenty enough for temperature to be meaningful. You can't meaningfully say that an atom contains thermal energy or has a temperature, can you! You cn extend this to a gas but the gas would have to be contained so that it doesn't disperse.

Quote from: yor_on
That should mean that you need more than the random movement of one lone particle to create heat.
As I said in my last post that is not what heat is. Heat is thermal energy which is flowing. No body can be said to contain heat. You're once a again confusing heat with thermal energy.

Quote from: yor_on
So it is then particles of restmass interacting with each other that creates radiation,..
No. Radiation is caused when either an atom collides with anothter atom and excites it to a higher energy level or a photon hits it and does the same thing. When the atom transitions to a lower energy state it emits a photon whose energy is the difference of the two energy levels of the atom.
 

Offline alancalverd

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If you want to consider a "perfect" vacuum, with no particles apart from your thermometer, you could put your thermometer in intergalactic space, far from any wandering planets, stars or gas clouds. In this case, the temperature of the thermometer would slowly decline until it approached around 2-3 Kelvin, which represents thermal equilibrium with the Cosmic Microwave Background Radiation.

So I would have to conclude that a vacuum does have a temperature.

Beg to disagree. Intergalactic space by definition is not a vacuum because it contains galaxies. If you isolate a bit of it that doesn't contain any matter and is a long way from any galaxy, it may indeed be permeated by CMB, but if you isolate a bit that is near the sun, for instance, your thermometer will get a lot hotter because there is a lot more radiation permeating your test space. And if you use a conducting box to isolate your test region, there won't be any CMB inside it. However the box will eventually equilibrate to 3K and start to radiate, hence warming your thermometer (assuming you cooled it to below 3K to start with).   
 

Offline Ophiolite

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Beg to disagree. Intergalactic space by definition is not a vacuum because it contains galaxies. 
Sorry, by definition intergalactic space is the space between galaxies. Consequently it contains no galaxies.
 

Offline PmbPhy

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People are getting too litteral when they use the term "vacuum" here. A vacuum is a region of space that is devoid of matter (in the classical sense). It isn't used to refer to regions of space that have absolutely nothing in it. The region of space such as that between the earth and moon is a very good vacuum but it's not a perfect vacuum because it has a few hundred atoms per cubit meter. That kind of region of space is referred to as a partial vacuum. So when you read a physics text which speaks about things such as the speed of light in free space or a vacuum this is what they mean. Otherwise they'd be talking about something that doesn't exist.
 

Offline yor_on

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Nice to see you too Burning :)
Long time no see.


as for what I mean, that depends, doesn't it? If I imagine a vacuum to be 'something', which I will do for this, then I also will say that we only have the properties of heat and temperatures when you have both existent. Am I wrong in this?
 

Offline yor_on

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Pete? What about the definition of a 'perfect vacuum' then? Don't you agree on that one? From relativity, or from some other interpretation?
 

Offline evan_au

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Quote
the speed of light in free space or a vacuum

The refractive index of air is 1.000277, ie the speed of light in air is just 0.3% slower than in a "perfect" vacuum. To a visible-light photon, the Earth's atmosphere is a pretty good vacuum (on a cloud-free day). And yet we feel the wind and need it air for life.

  • A cubic meter of holds 2x1025 molecules of air.
  • The Sun's corona has a density of around 1016 particles per cubic meter, or a billion times less dense than the Earth's atmosphere.
  • Some cosmological estimates put the density of the entire universe at around 1 proton per 4 cubic meters.
  • Presumably, the space between galactic clusters would be below this average.
So perhaps the question has no physical application, since there is no perfect vacuum.

But it's still useful as a thought experiment, to consider:
  • the photon temperature of the CMBR.
  • Dark matter still exists in a volume which contains no atoms or ions. There is an important theoretical question of the temperature of Dark Matter, as this temperature is thought to shape the cosmos that we see.
« Last Edit: 25/06/2014 21:22:53 by evan_au »
 

Offline jccc

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Suppose the outer part of the universe expending speed is equal or bigger than light speed, then we cannot detect any stars pass that distance, how can we know what's out there?

 

Offline yor_on

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If you want a Big Bang with a temperature, and heat, I would expect one to need this 'collection of particles' first, to interact with whatever definition of 'energy' one might define (pre)existing. That's about it I think and admittedly a weird proposal, still it seems to be correct. And it uses two uncertainties, first of all it defines 'energy' as something existing on its own, which I know no experimental agreement on? Is there any proof for this? Secondly it seems to me to define a preexisting dimension for it, in which it then interact with itself, creating 'bosons' and 'fermions'. How else can it be 'contained'?
 

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