Re: Dark matter/energy - is it real?


"Erik Max Francis" <max@xxxxxxxxxxx> wrote in message
news:ceKdnUQzxdHJt63ZnZ2dnUVZ_uWdnZ2d@xxxxxxxxxxxxxxxx

Dark matter is apparently supposed to be some form of non-luminescent
matter, but what is dark energy supposed to be?

The existence of dark matter is inferred by, among other things, looking
at galactic rotation curves.


All that tells us is that our theories of how fast they should spin are
wrong, it does *not* tell us why. Dark matter is a shim to make existing
theories work, nothing more. There are theories that explain the variation
without dark matter.




We can see galaxies spinning, and we can
measure how fast the matter in them is moving (due to Doppler shift). By
doing this, we see that they're moving much faster than they would be if
only the glowing matter we see were there. That is, if our theories of
gravity are anything like correct, there must be a lot of matter there we
can't see.

This really isn't all that surprising; the fundamental concept of dark
matter is not all that mysterious. Most of the matter around you consists
of dark matter: It does not emit its own light.


That is not what dark matter is.

Dark matter is not just matter that doesn't glow, it's entirely different.

Dark matter is non-baryonic. Which is to say it isn't made of baryons.
Since protons and neutrons are baryons, dark matter isn't made up of protons
and neutrons.

We know it's non baryonic because we know approximately how many baryons the
big bang made. For baryonic matter to be the missing mass there would have
to be about ten times as many as the theory predicts.

That leaves another form of matter. But there's a huge hole in the theory
of dark matter- if the universe is mostly made up of it, where is it? Why
don't we see any on Earth? Why do no known physical processes create it?
It's not that it's undetectible- we would notice that energy was missing
from reactions (which is how we found the neutrino).

Dark matter, if it exists and judging by the ways galaxies rotate, isn't
distributed right either. It would have to itself be unaffected by gravity
while affecting non-dark matter, but organize itself into halos around
galaxies for some unknown reason.




Dark energy is a more recent discovery (and is named to be similar to dark
matter even though it's not necessarily a related phenomenon).


It isn't a discovery because it hasn't been discovered. It's just a theory
to explain anomalous observations.





Dark matter and energy are really only the names we give to phenomenon
that we can logically conclude must be taking place if our understanding
of gravity and matter (and so on) are remotely correct.


There's no law that says our understanding *is* correct. Newton was fine
until applied at very high speeds. Now Einstein is fine until applied at
very long ranges and very high masses.




So far they are extremely good theories,


Except for the bits they don't explain, which means everything is a good
theory.




What would happen to the
calculations if the speed of light was variable over vast distances
(which we are currently unable to measure)? If the force of gravity was
variable on the large scale?

The speed of light somehow changing would result in all sorts of
detectable effects which we don't see -- after all, this would affect
spectra significantly. To explain away dark matter _and_ energy, the
force of gravity wouldn't have to just change, it would have to reverse at
large scales in bizarre ways that would probably be hard to make
consistent. (You'd also probably have to explain why our current
understanding of gravity coincidentally works so well despite being so
wrong.)


Newton works but is wrong too. All we really know is that our theories work
on a planetary scale, but not on a galactic scale.

There are theories that explain our observations without dark matter-
MOdified Newtonian Dynamics (MOND) in particular. But it is also a shim,
just like dark matter, but a different kind.



.

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