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Could it be that darkmatter is actually the gravitational influence of regular matter that is situated out of the observable universe?

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  • $\begingroup$ Do you really mean dark matter, or in fact dark energy? $\endgroup$
    – ProfRob
    Jun 11, 2021 at 7:35
  • $\begingroup$ Dark matter is not situated outside the 'observable universe', it is mainly expected to be found clumped together surrounding most of the galaxies in our universe as dark matter halos. Dark energy instead is spread evenly through the universe and causes the accelerated expansion of the universe. Both of these have not been observed experimentally and we don't have much idea about them. $\endgroup$ Jun 14, 2021 at 15:37

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Scientists do not know what dark matter is. It is a placeholder name. It is called "dark" for two reason:

  • If it exists, it interacts at most very weakly with electromagnetic radiation. It is "dark" in this sense.
  • If it exists, we do not yet know what it is. Science is "in the dark" regarding dark matter in this sense.

Dark matter, whatever it is, and if it exists, is not "regular matter that is situated out of the observable universe". It acts at the galactic scale. A more descriptive name is perhaps "a mystery substance that makes galaxies rotate at rates contrary to the rate suggested by luminous matter". "Dark matter", for short.

I am not denigrating the concept of dark matter. Despite not being able to find candidates for what constitutes dark matter, the alternative attempted explanations for these galactic scale disparities between galactic rotation rates as suggested by luminous (i.e., non-dark) matter are that much worse than dark matter. A more descriptive name for these conjectures is "a mysterious non-substance and non-uniform variation to gravity that makes galaxies rotate at rates contrary to the rate suggested by luminous matter".

Could it be that dark matter is actually the gravitational influence of regular matter that is situated out of the observable universe?

You are perhaps thinking of dark energy, the need for which was only discovered recently. Science is even more "in the dark" regarding the nature of dark energy than it is regarding dark matter. Dark matter was first conjectured to exist in the 1930s to explain the galaxy rotation curve problem. Dark energy was first conjectured to exist in the 1998 to explain the accelerating expanding universe problem.

Just as there are contrarians who dispute the existence of dark matter, there are also contrarians who dispute the existence of dark energy. In both cases (dark matter and dark energy), the contrarians are in the minority. These contrarians do not however fall into the realm of crackpotism, at least not yet. The galaxy rotation curve problem and the accelerating expanding universe problem remain unsolved problems in science at the present time, with the leading candidates having the placeholder names "dark matter" and "dark energy".

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  • $\begingroup$ I think you could argue that dark energy, in the form of the cosmological constant in GR, was first postulated in 1917 to solve a different problem (which it didn't solve, and which was not in fact a problem). (Note, I'm not disagreeing with your answer!) $\endgroup$
    – user38308
    Jun 11, 2021 at 11:37
  • $\begingroup$ As well as galaxy rotation curves, dark matter is also important in gravitational lensing. $\endgroup$
    – PM 2Ring
    Jun 12, 2021 at 20:18
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    $\begingroup$ @PM2Ring Gravitational lensing is one of many things that show that something that is local, that is not visible, but that does have a gravitational effect does indeed exist. We don't know what it is, but it is there. Let's call it "dark matter" for short. $\endgroup$ Jun 12, 2021 at 20:34
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If dark matter exists (rather than some strange rewrite of physical laws), then it is required to be all around us. It could not be simulated by the effects of normal matter at great distances.

There are two other things to bear in mind.

(1) If you postulate there is stuff beyond the observable universe then, by definition, it can have no effect on us or our locality. Otherwise it would be observable, since the effects of gravity, like light, travel at the speed of light.

(2) There is other evidence found by combining what we know about the geometry of the universe (e.g., from the cosmic microwave background) and observations from which the primordial big-bang-produced chemical abundances of helium and deuterium are inferred, that most of the gravitating matter in the universe is not "normal matter" made of neutrons and protons.

If, as I suspect, you are actually trying to replace dark energy with matter beyond the observable universe then firstly, the caveat about things beyond the observable universe not affecting us locally still applies.

Secondly, in cosmology you need to use General Relativity to describe the dynamics of the universe as a whole. But, even if we were to adopt Newtonian gravity and consider some "shell" of material around the observable universe; that would not cause a stretching effect, because Newton's shell theorem tells us that the gravitational field inside a uniform shell is zero.

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  • $\begingroup$ So, what happens if we consider the observable universe of objects(stars, galaxies...), that are near the limit of earth's observable universe? Would they be affected by gravitational influence of objects outside earth's observable universe? A say that because it seems that the observable universe of such objects would extend beyond earth's, allowing them to be causally connected. Or am i just saying nonsense? $\endgroup$
    – sir_pi
    Jun 13, 2021 at 19:41
  • $\begingroup$ @sir_pi Sure, but that can't explain the dark matter required locally and also take note of what I said about the gravitational influence inside a shell being zero. $\endgroup$
    – ProfRob
    Jun 13, 2021 at 20:23

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