Taking the universes temperature

[higginsdj]

COBE and the Planke Explorer were/are designed to map the CMB which is effectively, the temperature of the 'universe'. Is this a correct statement?

if the statement is correct, then aren't they just taking the temperature of whatever is 'seen'? Now we are supposedly surrounded by a large volume of dark matter. Matter, must be warmer than its surrounding space, even if it is very cold, so might these CMB pictures be showing the location of Dark Matter?

(just been watching Stephen Hawkings Universe again)

Cheers

[xelasnave]

Have a look at this ..it is very basic but may help you understand a little more about dark matter
http://www.youtube.com/watch?v=9fIrmjxlT18
alex

[xelasnave]

You may find this of interest also
http://www.youtube.com/watch?v=pnLVZ4TbrCU
alex

[sjastro]

Originally Posted by higginsdj

COBE and the Planke Explorer were/are designed to map the CMB which is effectively, the temperature of the 'universe'. Is this a correct statement?

if the statement is correct, then aren't they just taking the temperature of whatever is 'seen'? Now we are supposedly surrounded by a large volume of dark matter. Matter, must be warmer than its surrounding space, even if it is very cold, so might these CMB pictures be showing the location of Dark Matter?

(just been watching Stephen Hawkings Universe again)

Cheers

What we are observing are photon energies at the time of recombination (when photons are absorbed/emitted by the earliest atoms formed in the Universe).

The photons are cosmologically red shifted into the microwave region. Since the CMB is a near perfect black body, we can calculate the temperature as a function of the photon energies. In our frame of reference this temperature is 2.7K.

The small variations in the CMB is due to temperature differences in the environment in which the photons existed at the time of recombination.
The cooler regions are where matter is ultimately able to form.
A smaller variation in the CMB is believed to have been caused by the effect of gravitiational waves caused by Inflation.

Regards

Steven

[CraigS]

Dark Matter is defined as being undetectable by emitted or scattered electromagnetic radiation (such as the CMBR). It is inferred to exist through its interaction with gravity and is thus observable via several means such as gravitational lensing or hi-energy neutrino emissions (via mutual annihilation).

The most likely candidate for dark matter in the current standard cosmological model is in the form of WIMPs (Weakly Interacting Massive Particles). They are theorized to be of relatively large mass, relatively slow moving (non-relativistic) and hence energetically, ‘cold’. They may be entirely transparent to the EM spectrum and thus, they wouldn’t be visible (or appear as ‘holes’), in the measured CMB spectra. Dark matter density information however, can be derived from part of the CMBR power density spectrum.

The Planck spacecraft has multiple objectives. One is to observe gravitational lensing of the CMB. We may learn more about the ‘clumpiness’ and locations of Dark Matter from the onboard technology. Lensing observed with the Hubble telescope has been used to create a 3D model of the large scale distribution of Dark Matter.

Hope this helps as an adjunct to Steven’s description of the CMBR.

Cheers.

[higginsdj]

Originally Posted by CraigS

Dark Matter is defined as being undetectable by emitted or scattered electromagnetic radiation (such as the CMBR).

I do find that definition a little odd. Its a bit like saying, a tree falls in the woods (because I heard it) but because I didn't see it, one can't ever see a tree falling.

Cheers

[CraigS]

Originally Posted by higginsdj

I do find that definition a little odd. Its a bit like saying, a tree falls in the woods (because I heard it) but because I didn't see it, one can't ever see a tree falling.

Cheers

The definition mentioned was not intended as the sole justification for Dark Matter’s hypothesized existence.

The mentioned aspect was only intended as an aspect relevant to CMBR measurements.

There are other reasons for it to exist in the Standard Model.

Cheers