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Dark Matter/Energy

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17 years 11 months ago #26792 by Son Goku
Dark Matter/Energy was created by Son Goku
I've been reading over old posts and it seems that quite a few people disagree with the ideas of Dark Matter and Energy in modern cosmology.

What do people find dubious about it?

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17 years 11 months ago #26813 by JohnMurphy
Replied by JohnMurphy on topic Re: Dark Matter/Energy
In a previous thread it was described as another "luminiferous ether".
I can understand to some extent peoples reservations on this topic. Again it is probably down to lack of observation, but that has been changing in recent times. You can't yet go into Lidl and buy a bag of dark matter, though I believe they're selling positrons for €25 a gram.

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John Murphy
Irish Astronomical Society
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17 years 11 months ago #26816 by voyager
Replied by voyager on topic Re: Dark Matter/Energy
Personally I have no problems with Dark Matter, there is ample evidence that there is mass galaxies that we cannot see. It may proove to be Nutrions since it is looking like they are not QUITE massless or if could be some cool non-barionic matter. Either way I'm happy to accept that there is matter that does not emit light in galaxies.

Dark energy on the other hand seems to be going out on a bit of a limb to me. The experimental data is not as clear cut and it just strikes me as a desperate attempt to hold on to old theories we like despite observations not really agreeing with the old theories.

I'm open to a more enlightened and educated perspective on this lot though.

Bart.

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17 years 11 months ago #26823 by Son Goku
Replied by Son Goku on topic Re: Dark Matter/Energy

Dark energy on the other hand seems to be going out on a bit of a limb to me. The experimental data is not as clear cut and it just strikes me as a desperate attempt to hold on to old theories we like despite observations not really agreeing with the old theories.


Funnily enough most people on the net have more of a problem with Dark Matter, even though, as you said, it is the one with more experimental evidence.

For anybody whose is interested, the motivation for Dark Energy is as follows:
General Relativity is described by the following equation:

It doesn't matter what the terms mean, just the lambda term, which is the cosmological constant.
In the early years of General Relativity, most relativists set this to zero since it makes General Relativity much easier to solve.
(Although even then GR is pretty much impossible to solve.)
At one point Einstein, as I'm sure you've all heard, assumed it had a small value which turned out to be incorrect.

However in recent years it has been seen that the universe is expanding, so Cosmologists went back to General Relativity to see if this matched what it predicted.
It turns out General Relativity does predict it, when you have a very small lambda.

The problem is General Relativity doesn't say were lambda comes from.
So now we're in the unusual position of having something which matches our theory, but as no explanation.

In recent years, some people have proposed that lambda is caused by Dark Energy.

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17 years 11 months ago #26840 by JohnMurphy
Replied by JohnMurphy on topic Re: Dark Matter/Energy
Also, the value of lambda has probably changed over the evolution of the universe. It is not necessarily a constant, and I believe Einstein must have been very frustrated at having to introduce a constant with an unknown value, that will likely have different values at different points in time.

In recent years, some people have proposed that lambda is caused by Dark Energy.

i.e. that an increase in Dark Energy will cause greater expansion of the Universe - if I'm reading that correctly.
This then starts a chain of questions like:
where is the 'new' dark energy coming from?
for a given amount of dark energy we get a period of expansion which must eventually equalize.?
Maybe we need a "new" equation:
Dark E = Dark m (c*c)
Therefore dark energy and dark matter are interchangeable.
The question I would have is - is dark matter and dark energy interchangeable with energy and matter as we currently know it - probably not as it would be a lot easier to detect etc.

Speaking of detection - there are currently surveys going on into the distribution of dark matter in our own Galaxy. I don't know how they are doing this, but I would presume that they look at the angular momentum of stallar objects in say clusters, the total mass and then ask the question "can we see enough mass to justify the angular momentum?", if not then just add quantity x amount of dark matter to that area of the galaxy and hunky dory everything is now balanced. Please tell me I'm wrong - that there is a neater way of detecting dark energy.

Clear Skies,
John Murphy
Irish Astronomical Society
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17 years 11 months ago #26851 by dave_lillis
Replied by dave_lillis on topic Re: Dark Matter/Energy
What do people think of the theory regarding the source of "dark matter" or more accurately its gravitational effect, in that this excess gravity is actually normal gravity leaking from other parallel universes into ours.
The theory suggests that matter seems to be unable to crossover, except gravitons which supposedly can. This explains the extra gravity that
"dark matter" supplies.
Given that dark matter cannot emit nor reflect light and seems to be completely undetectable so far except through gavity, is this theory totally off the wall, has it been debunked/surpassed or is there serious work going on in this.

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