# The Naked Scientists Forum

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Background electromagnetic radiation in space
« on: 07/10/2014 16:29:35 »
We are informed that the temperature of outer galactic space is 2.7 deg.K in all directions.   The space is empty and dark so does anyone know how many joules of energy a cubic kilometre will contain  to keep itself warm?
CliveS

#### evan_au

• Neilep Level Member
• Posts: 4109
• Thanked: 245 times
##### Re: Background electromagnetic radiation in space
« Reply #1 on: 08/10/2014 08:47:50 »
There is a big difference between the energy space contains, and the energy you can extract from it.

We are used to extracting energy by a "heat engine", which relies on having a difference of temperature between two adjacent points. However, if your cubic kilometer of space at 2.7K is surrounded by other cubic kilometers also at 2.7K, then you can't extract any energy via a heat engine.

This just leaves the energy you can extract from the very low energy microwave photons that make up the 2.7K black-body background radiation.

There is still dark matter & dark energy - but we currently don't know of any way to extract energy from these sources.

#### syhprum

• Neilep Level Member
• Posts: 3818
• Thanked: 19 times
##### Re: Background electromagnetic radiation in space
« Reply #2 on: 08/10/2014 11:27:23 »
We know that the 6000K radiation from the sun deposits approximately 1.2KW per square meter at 1 AU from this can we derive how much power per square meter we could obtain from the CMBR ?.
My sub "O" level maths says .004nW !

WIKI says 3 microwatts !
« Last Edit: 08/10/2014 15:27:01 by syhprum »

#### JohnDuffield

• Sr. Member
• Posts: 488
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #3 on: 08/10/2014 12:31:51 »
We are informed that the temperature of outer galactic space is 2.7 deg.K in all directions. The space is empty and dark so does anyone know how many joules of energy a cubic kilometre will contain to keep itself warm?
See what evan said. If you took away all the energy associated with that 2.7 degrees, space still contains "vacuum" energy. As to how much, nobody knows. For an analogy, imagine you're in a boat out at sea. The little ripplets on the surface of the sea equate to the CMBR. The vacuum energy equates to the depth of the sea.

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #4 on: 08/10/2014 14:05:41 »
John
That is very interesting. I tend to agree that intergalactic space is not empty but contains some magnetic vacuum massless energy; otherwise the temperature would be 0deg.K wouldn't it?
CliveS

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1872
• Thanked: 143 times
##### Re: Background electromagnetic radiation in space
« Reply #5 on: 08/10/2014 17:54:53 »
There are many reasons that none of the universe is 0 K. Some has to do with zero point energy, some has to do with the fact that nothing will spontaneously surrender thermal energy to anything that isn't colder than it is, so there is no mechanism for thermal equilibration to achieve 0 K anyway.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11987
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: Background electromagnetic radiation in space
« Reply #6 on: 08/10/2014 18:32:11 »
It's difficult. Some define EM radiation as a temperature. The temperature we normally mean though is a interaction between radiation (sun light) and rest mass (your skin). Myself I lean to the last definition and therefore have a clear problem with stating that 'photons' left over from a Big Bang in 'deep space' has a temperature in themselves, without interaction with some type of other particles of rest mass. It's the kinetic energy of the rest mass that then express itself as a temperature when interacting with the sun for example, and that goes for a vacuum too. There are some arguments why nothing can reach a temperature of zero. One is HUP (Heisenberg's uncertainty principle) forbidding it. http://www.thescienceforum.com/chemistry/2512-absolute-zero-print.html and http://www.physlink.com/education/askexperts/ae380.cfm

The other should be "that the efficiency of heat pumps as coolers falls to zero as the temperature falls to zero. So with any heat leak, no matter how small, it would require an infinite amount of work to cool something to absolute zero. " which then is a argument from thermodynamics. http://van.physics.illinois.edu/qa/listing.php?id=1046

Temperature as such is a interaction between radiation and some measurement by rest mass. So sure, those 'photons' when connecting with our instruments will give us a temperature. That doesn't mean that deep space in itself has this temperature by itself, although as soon as it meet a particle of rest mass out there, that rest mass will start to 'vibrate'.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11987
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: Background electromagnetic radiation in space
« Reply #7 on: 08/10/2014 18:53:19 »
What I think I'm trying to say is that a pure vacuum, ideally :) should be defined as without radiation. Now, such a vacuum, can it exist? What about HUP, if so?

#### evan_au

• Neilep Level Member
• Posts: 4109
• Thanked: 245 times
##### Re: Background electromagnetic radiation in space
« Reply #8 on: 09/10/2014 02:25:59 »
Quote from: chiralSPO
there is no mechanism for thermal equilibration to achieve 0 K anyway
I agree that you will never reach 0 K, but the general expansion of the universe will make the temperature of the background radiation approach 0 K (as a limit).

If we ignore major effects like Dark Energy and Starlight, I assume that the background temperature would drop to something like 1.3 K after another 13 billion years or so?

As for me, I think I'd like to stay toasty warm with my 1kW/m2 from the Sun.

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #9 on: 09/10/2014 09:21:01 »
On one of the other forums, I received a reply that as Stefan Boltzmann constant is 5.67 * 10^-8 that the background energy at 2.7 deg.K should be 1.04 joules per square metre which he thinks makes 1.96 * 10^-5 Joules per cubic metre?  Seems high to me as I would expect the magnetisation energy of empty space to be much less even Pico-joules per cubic kilometre.
CliveS

#### JohnDuffield

• Sr. Member
• Posts: 488
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #10 on: 09/10/2014 12:12:16 »
That is very interesting. I tend to agree that intergalactic space is not empty but contains some magnetic vacuum massless energy; otherwise the temperature would be 0deg.K wouldn't it?
Don't get distracted by "magnetic vacuum massless energy". An  electromagnetic field has energy, and that energy has a mass equivalence. In addition, an electromagnetic wave is a field variation. There's an electromagnetic field of sorts right there in empty space. In QED they refer to it as the photon field. Have a look at http://arxiv.org/abs/1209.0563 which is about vacuum energy, and check out the vacuum catastrophe.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11987
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: Background electromagnetic radiation in space
« Reply #11 on: 09/10/2014 17:06:48 »
all of it interesting, but what is a perfect vacuum?

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4704
• Thanked: 153 times
• life is too short to drink instant coffee
##### Re: Background electromagnetic radiation in space
« Reply #12 on: 09/10/2014 19:11:37 »
A hole with nothing in it.

#### syhprum

• Neilep Level Member
• Posts: 3818
• Thanked: 19 times
##### Re: Background electromagnetic radiation in space
« Reply #13 on: 09/10/2014 21:56:02 »
I was hoping that someone with better than "sub O level maths" would tell me why my estimate is so different from the WIKI value.

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3916
• Thanked: 53 times
• The graviton sucks
##### Re: Background electromagnetic radiation in space
« Reply #14 on: 09/10/2014 22:32:15 »
That is very interesting. I tend to agree that intergalactic space is not empty but contains some magnetic vacuum massless energy; otherwise the temperature would be 0deg.K wouldn't it?
Don't get distracted by "magnetic vacuum massless energy". An  electromagnetic field has energy, and that energy has a mass equivalence. In addition, an electromagnetic wave is a field variation. There's an electromagnetic field of sorts right there in empty space. In QED they refer to it as the photon field. Have a look at http://arxiv.org/abs/1209.0563 which is about vacuum energy, and check out the vacuum catastrophe.

Vacuum catastrophe. Why? It is just we don't know the cause. Maybe catastrophic for physicists. Is anything a contributor to this energy? Surely there must be. Energy is radiated into the vacuum.

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #15 on: 10/10/2014 10:27:45 »
I have just been advised from another forum that the estimated value of energy per cubic metre for the whole universe is 10^-9 Joules/m^3 which assumes that 4.5% is baryonic matter and 95.5% dark energy and dark matter.  If dark energy and dark matter do not exist then the total energy in the universe would average at 4.5*10^-11 Joules/m^3 and the dark force pushing the galaxies apart could just be a magnetic force provided by the 2.7deg.K background space energy.
CliveS

#### yor_on

• Naked Science Forum GOD!
• Posts: 11987
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: Background electromagnetic radiation in space
« Reply #16 on: 10/10/2014 18:06:44 »
Thanks Alan, a hole with nothing in it should be sufficient for defining a perfect vacuum.
Now, does such a thing exist?
=

Maybe we should define it as a SpaceTime location, containing nothing except that vacuum. No radiation and no 'virtual particles', just to be on the safe side :)
« Last Edit: 10/10/2014 18:10:06 by yor_on »

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4704
• Thanked: 153 times
• life is too short to drink instant coffee
##### Re: Background electromagnetic radiation in space
« Reply #17 on: 10/10/2014 22:35:18 »
Thanks Alan, a hole with nothing in it should be sufficient for defining a perfect vacuum.
Now, does such a thing exist?

No. The gap between galaxies contains fewer molecules per unit volume than anything we can manufacture, but there are still a few bits of stuff out there. The Bohr atom has a perfect vacuum between the electrons and the nucleus, but Schrodinger allows the electron to be anywhere and everywhere if we wait long enough.

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #18 on: 11/10/2014 09:40:43 »
If we have a perfect vacuum it will have a volume but no mass. If I magnetise that vacuum it still has no mass and the same volume but it has aligned itself in orientation and that is the difference.  Is it possible to re-orientated a vacuum without expending energy??  CliveS

#### PmbPhy

• Neilep Level Member
• Posts: 2760
• Thanked: 38 times
##### Re: Background electromagnetic radiation in space
« Reply #19 on: 11/10/2014 10:50:54 »
Where there are charges present there is a field even in what you'd call a vacuum and a field has mass density.

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4704
• Thanked: 153 times
• life is too short to drink instant coffee
##### Re: Background electromagnetic radiation in space
« Reply #20 on: 11/10/2014 11:27:23 »
If I magnetise that vacuum it still has no mass and the same volume but it has aligned itself in orientation and that is the difference.

Beware of imprecise language. You can create a magnetic field in a vacuum, but "magnetise" means to orient particles with magnetic dipoles. The magnetic resonance signal from a vacuum is zero.

#### acsinuk

• Sr. Member
• Posts: 235
• Thanked: 1 times
##### Re: Background electromagnetic radiation in space
« Reply #21 on: 11/10/2014 20:06:33 »
Thanks, but we need an answer to the question? Can we magnetise dipole space with zero energy?  It is accepted that quadrupole molecules have hysteresis loss so are a special case.
Does the constant nuclear magnetron of 3.1*10^-9 Kelvin/turn refer to these molecules only?
CliveS

#### The Naked Scientists Forum

##### Re: Background electromagnetic radiation in space
« Reply #21 on: 11/10/2014 20:06:33 »