Could Dark Energy be a form of Dark Matter

  • #1
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Main Question or Discussion Point

Dark Energy is said to be present in order to drive the observed acceleration of the expansion of the universe and Dark Matter is hypothesised to be present to drive observed gravitational effects.

Would a large mass of dark matter distributed around the outer parts of the universe have the same effect as the mooted Dark Energy, as its attraction would tend to draw all the other material towards it, thus accelerating the outward movement.
 

Answers and Replies

  • #2
Drakkith
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No, dark energy and dark matter are distinctly different things. Furthermore, there are no "outer parts" of the universe. The universe is not believed to have any edges.
 
  • #3
Chronos
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The only connection between dark matter and dark energy is linguistic - dark, meaning we don't know what it is. If they are connected, that would be a remarkable coincidence.
 
  • #4
mathman
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Dark matter is stuff - we just don't know what. It is "observed" by its gravitational effect.

Dark energy, which may not even be energy, is something responsible for the acceleration of the universe expansion.
 
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  • #5
Chronos
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The 'we don't know what it is' meaning of the term dark was applied to this weird 'energy' hypothesized to exist as a result of supernova studies [re: Perlmutter, et al]. But 'we don't know what it is' could have been applied to the coelacanth and the recently discovered algae prototheca cutis. If biologists had the same laid back attitude as cosmologists, they could have just as easily allowed them to be called 'dark fish' and 'dark algae'. Similarly, the recently discovered meteoritic mineral, panguite, could just as easily been called 'dark mineral' by indifferent geologists. It would not have taken much to grow legs for conspiracy theories linking the three, and then with dark matter and dark energy. Imagine the pandemonium that would ensue should physicists discover a weird new elementary particle and, unable to decide who gets the credit, chose to allow the media to call it the 'dark particle'.
 
  • #6
mathman
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The 'we don't know what it is' meaning of the term dark was applied to this weird 'energy' hypothesized to exist as a result of supernova studies [re: Perlmutter, et al]. But 'we don't know what it is' could have been applied to the coelacanth and the recently discovered algae prototheca cutis. If biologists had the same laid back attitude as cosmologists, they could have just as easily allowed them to be called 'dark fish' and 'dark algae'. Similarly, the recently discovered meteoritic mineral, panguite, could just as easily been called 'dark mineral' by indifferent geologists. It would not have taken much to grow legs for conspiracy theories linking the three, and then with dark matter and dark energy. Imagine the pandemonium that would ensue should physicists discover a weird new elementary particle and, unable to decide who gets the credit, chose to allow the media to call it the 'dark particle'.
Your point?
 
  • #7
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Would a large mass of dark matter distributed around the outer parts of the universe have the same effect as the mooted Dark Energy, as its attraction would tend to draw all the other material towards it, thus accelerating the outward movement.
could be...if by 'outer parts' you mean beyond the observable universe.....but there is no mainstream theory to provide such a configuration...nor a reasonable rationale. In fact the mainstream FLRW cosmological model posits something quite different.....that space looks everywhere the same on large scales....The FLRW metric starts with the assumption of homogeneity and isotropy of space.


also, why posit 'large dark matter', just posit lots of regular mass, way out there.
 
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  • #8
Drakkith
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could be...if by 'outer parts' you mean beyond the observable universe.....but there is no mainstream theory to provide such a configuration...nor a reasonable rationale. In fact the mainstream FLRW cosmological model posits something quite different.....that space looks everywhere the same on large scales....The FLRW metric starts with the assumption of homogeneity and isotropy of space.


also, why posit 'large dark matter', just posit lots of regular mass, way out there.
I don't think it would be the same. The expansion causes recession velocities to increase linearly, while gravity should cause it to increase exponentially, right?

Also, wouldn't this kind of setup be similar to a hollow sphere where the net force inside is zero?
 
  • #9
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I don't think it would be the same. The expansion causes recession velocities to increase linearly, while gravity should cause it to increase exponentially, right?

Also, wouldn't this kind of setup be similar to a hollow sphere where the net force inside is zero?
I can't think of anything that would really be the 'same' as a uniform cosmological constant or an equivalent uniform distribution throughout all of space.....That's likely a better answer.
 
  • #10
Astronuc
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This may help somewhat with the distinction between DE and DM.
http://home.web.cern.ch/about/physics/dark-matter

Dark matter
Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter. Dark matter seems to outweigh visible matter roughly six to one, making up about 26% of all the matter in the universe.
Dark energy
Dark energy makes up approximately 70% of the universe and appears to be associated with the vacuum in space. It is distributed evenly throughout the universe, not only in space but also in time – in other words, its effect is not diluted as the universe expands. The even distribution means that dark energy does not have any local gravitational effects, but rather a global effect on the universe as a whole. This leads to a repulsive force, which tends to accelerate the expansion of the universe.
My embolding for emphasis.

See also - http://hubblesite.org/hubble_discoveries/dark_energy/de-what_is_dark_energy.php
 
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