What will the universe be composed of

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In summary, the conversation discusses the values of dark matter and mass in the universe, specifically when the universe is five times its current size. The person speaking mentions previous calculations they have done and asks for a second opinion on the numbers. Another person confirms the calculations and notes that it's always good to have someone else check for errors.
  • #1
jc09
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How can we tell the values of dark matter and mass in the universe when it is say five times its original size?
 
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  • #2
jc09 said:
five times its original size?

What do you mean by "original size"?
 
  • #3
jc09 said:
How can we tell the values of dark matter and mass in the universe when it is say five times its original size?

Nabeshin said:
What do you mean by "original size"?

That's the logical question to ask, for sure. Nabeshin you seem really knowledgeable and reliable----would you be willing to check me on some numbers?

Some years back I took the usual numbers we were hearing, on critical (energy) density and dark matter fraction and dark energy fraction and I imagined everything put into energy terms (instead of grams per unit volume, say joules).

And I recall getting something like this for the CURRENT energy densities:

Critical density today was around 0.85 nanojoule per cubic meter, and the U looks flat or nearly flat so let's say the real overall average density is 0.85 nJ/m3

And then dark energy density (which in the standard cosmo model stays constant) comes out to about 0.6 nJ/m3.

I suppose the OP ("jc09") could be asking what the densities would be like when distances have expanded by a factor of cuberoot 5 and when volumes are 5 times what they are NOW.
(he could mean "present" instead of "original")

So then because the dark matter fraction is around 23 or 24% of the mix now, which translates to
about 0.20 nJ per cubic meter, it would then be 0.04 nJ per cubic meter.
And ordinary matter is now about 0.03 nJ per cubic meter, so when volume is 5 times what it is now the ordinary would be down to the level of roundoff error.

What is 0.03 divided by 5? 0.006. Doing rough estimates we can forget that.

So the present densities are about 0.6 nJ per cubic meter DE
and about 0.2 nJ per cubic meter DM

and in future when volume has increased by factor of 5 we will have
0.6 nJ per cubic meter DE (because in standard LCDM cosmology it does not change) and
0.04 nJ per cubic meter DM

My aim is to say something concrete at an effective pedagogical level. I'd welcom any comment correction or improvement
It may also be irrelevant to the OP question since he or she may not have meant 5 times bigger than present, when they said 5 times bigger than original.
 
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  • #4
marcus said:
would you be willing to check me on some numbers?

Yep, checks out!
 
  • #5
Nabeshin said:
Yep, checks out!

Thanks! This is an example of how well PF astro/cosmo forum can work sometimes. I probably trust you on numbers and technical detail more than I trust myself, so it's reassuring to hear from you something checks out.
 
  • #6
marcus said:
I probably trust you on numbers and technical detail more than I trust myself, so it's reassuring to hear from you something checks out.

Haha! This is a scary thought though!

It definitely is nice to have someone check your work, especially when you're doing numerical answers where order of magnitude errors sometimes creep in unnoticed :)
 

What will the universe be composed of?

The exact composition of the universe is still a mystery, but we do have some understanding of its major components. According to current theories and observations, the universe is composed of ordinary matter, dark matter, and dark energy.

What is ordinary matter?

Ordinary matter, also known as baryonic matter, is the type of matter that we can see and interact with. This includes atoms, which are made up of protons, neutrons, and electrons. Ordinary matter only makes up about 5% of the total mass of the universe.

What is dark matter?

Dark matter is a type of matter that does not emit or absorb light, making it invisible to telescopes. It is estimated to make up about 27% of the universe's mass. Its presence is inferred through its gravitational effects on visible matter and the structure of the universe.

What is dark energy?

Dark energy is a mysterious force that is believed to be responsible for the accelerated expansion of the universe. It makes up about 68% of the universe's energy density. Its exact nature is still unknown, but it is thought to be a property of space itself.

Will we ever fully understand the composition of the universe?

As our understanding of physics and the universe continues to evolve, we may eventually have a better understanding of the composition of the universe. However, it is possible that some aspects may always remain a mystery, as there is still much we do not know about the universe and its origins.

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