Universe Expansion

Discussion in 'Pseudoscience' started by hansda, Aug 24, 2017.

  1. hansda Valued Senior Member

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    We know that our universe is expanding, as observed by Edwin Hubble.

    Is this expansion spherical, ie radial expansion in all directions?

    OR, this expansion is spiral, as if a coiled spring is uncoiling?
     
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  3. mathman Valued Senior Member

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    It appears to be "radial". Distance galaxies are moving away with speed depending only on distance.
     
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  5. timojin Valued Senior Member

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    If the universe is expanding does the temperature decreases also
     
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  7. origin Trump is the best argument against a democracy. Valued Senior Member

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    Yes.
     
  8. mathman Valued Senior Member

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    The temperature drop is best seen from the microwave background, which has a temperature ~ 3 deg K, compared to several thousand degrees around 300,000 years after the big bang.
     
  9. The God Valued Senior Member

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    This is very complex. It involves dependence of electromagnetic radiation on temperature, volume and of course the constancy of entropy under adiabatic expansion. Too many assumptions.
     
  10. The God Valued Senior Member

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    Einstein original equations leads to expansion (or collapse) but he proposed static universe with his cosmological constant. Later on Hubble observation could be explained with expansion only, which further on proposed as accelerating expansion based on redshifts observations. This could only be spherical with visible horizon till recession velocity becomes c.
     
  11. Boris2 Valued Senior Member

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    The Observable Universe is a spherical volume. We don't know the shape of the Universe, and it probably has no meaning anyway.

    Probably only in intergalactic space where expansion is manifest.
     
  12. James R Just this guy, you know? Staff Member

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    Everything moves away from everything else, on large enough scales.

    But don't let that give you the idea that there's a centre that things are moving away from. There was no big bang at a centre, from which everything then moved away. The big bang happened everywhere at once.
     
  13. Write4U Valued Senior Member

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    That seems to be the case which IMO argues for initial very fast expansion from a small singularity and it does so in a wave like manner. Is there a possibility that our expansion has its own frequency and may be we are caught in one of the frequency cycles and our spacetime expansion will slow or speed up in accordance to this frequency.
    There was an article on the "ringing universe" which illustrated the universe as having gone through , I believe 7 cycles of contraction and expansion during its 14.5 billion years existence. How can we tell where we are on the Pilot Wave, we may be expanding now but could there be a limit of expansion at the top of the wave and begin to decrease in the next 2 billion years ......

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  14. exchemist Valued Senior Member

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    I had understood it was very simple: the expansion of space leads to an increase in wavelength, which is a reduction in frequency, which shifts the envelope of the black body radiation towards the red.
     
  15. The God Valued Senior Member

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    So how does temperature decrease with increase in wavelength, decrease in frequency and subsequent shifting towards red ?
     
  16. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    Are you asking why the temperature decreases when there is a decrease in frequency, or are you asking the mechanism by which this occurs?

    Beyond that, if the universe is, in fact, a closed system, and we know that energy can neither be created nor destroyed, but only change form, and that the universe is expanding...

    Logically, it should follow, that the universe is cooling, as the energy density is decreasing (fixed value of energy against an increase value of volume, resulting in a reduction in density of energy).
     
  17. The God Valued Senior Member

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    All fine, volume increases but how does temperature decreases in this process?

    Please note that I have cautiously stayed away with a caution that it is quite complex and stated the required ingradients, but Exchemist feels that it is pretty simple as increase in wavelength etc will reduce T. How is it so simple?

    PS: BTW thanks for starting to follow me. I promise you a great, objective but not necessarily pleasing to authority, learning.
     
  18. timojin Valued Senior Member

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    Ok the black body. But in this case who the emission source that with increasing the distance that caused the shift of frequency ?
     
  19. DaveC426913 Valued Senior Member

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    Can you rephrase? I can't parse that sentence.
     
  20. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    If you have a set amount of energy that cannot increase, and the volume said energy is spread out across increases, the energy density will decrease. As a result, the temperature has decreased (after all, thermal emission is just a form of radiated energy).

    Conservation of Energy at work, I believe.


    As above - it is basic conservation of energy... unless I'm misunderstanding what it is you are questioning?
     
  21. exchemist Valued Senior Member

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    6,474
    Look up black body radiation, if you do not now what that is. But in a nutshell, (a) a thermal emitter gives off radiation with a characteristic frequency distribution, and (b ) the relative amounts of the various frequencies emitted depend on the temperature of the object. This is why a heated piece of iron will, as the temperature rises be first red hot, then yellow, and then white hot.

    The Wiki article on CMBR, here: https://en.wikipedia.org/wiki/Cosmic_microwave_background has, as usual, a good description.

    In the case of our universe, the initial temperature of the CMBR would have been defined at the moment the universe became transparent to radiation for the first time, and it has subsequently expanded with the expansion of space.
     
  22. The God Valued Senior Member

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    Kittamaru, that's very simplistic but actually it is not. The expansion here could be isothermal or adiabatic. Say it is not isothermal, so the next step is to establish that the adiabatic expansion of the universe will decrease the temperature, to establish that for non fluid expansion of this type you have to bring in maths which will involve V and T with some power and related inversely. Can you do it for radiation? Hint : It's complex and will involve entropy too, that's why I said, it's complex.
     
  23. timojin Valued Senior Member

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    When the red shift was measured . For us on the earth to se the shift taken place, who was the light source ?
     

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