A new paper on the arXiv by Hossenfelder and Mistele shows impressive
agreement between the predictions of a
superfluid dark matter model and actual measurements on 64 of a set of 65
galaxies. The model falls somewhere between particle dark matter models and
modified gravity models. I find that while the model gets the effects right it
attributes them to the wrong physics. However, it may be the best that can be
done by physicists who are working in the current paradigm and are unaware of
the spacetime model that I’ve been covering in this blog. In this post I’ll
show where Sabine is right and where she’s wrong.
Here’s Sabine, in a blog
post about her paper:
Physicists
still haven’t figured out what dark matter is made of, if anything. The idea
that it’s made of particles that interact so weakly we haven’t yet measured
them works well to explain some of the observational evidence. Notably the
motions of galaxies bound to clusters and the features of the cosmic microwave
background fit with theories of particle dark matter straight-forwardly. The
galaxies themselves, not so much.
Astronomers
have found that galaxies have regularities that are difficult to accommodate in
theories of particle dark matter, for example the Tully-Fisher relation and the
Radial Acceleration Relation. These observed patterns in the measurements don’t
follow all that easily from the simple models of particle dark matter.
One of
the proposals ,,, has long been that gravity must be modified. ,,, modified
gravity works dramatically well for galaxies and explains the observed
regularities.
She explains that three years ago she read a
paper that proposed that dark matter is a superfluid—light particles that
condense under pressure to form a superfluid. The proposed superfluid is
crawling with phonons, which result in a force that interacts with normal
matter. She goes on:
This
force looks like modified gravity. Indeed, I think, it is justified to call it
modified gravity because the pull acting on galaxies is now no longer that of
general relativity alone.
Here Sabine correctly concludes that dark
matter causes an additional force that modifies the effects of gravity. However,
there is no superfluid matter. In fact, there is no matter at all, just energy
in the form af oscillations of space that are left over at the end of inflation
after the reheating or particle formation period, as I explained here.
These oscillations are not phonons, buy they are energy and therefore have a
gravitational force, which is dealt with quite well, thank you, by General
Relativity alone. The force doesn’t modify gravity, it simply increases the
gravitational force acting on the normal matter. But yes, it does look like
modified gravity. Back to Sabine, on getting the dark matter to condense and
form a superluid:
However,
to get the stuff to condense, you need sufficient pressure, and the pressure
comes from the gravitational attraction of the matter itself. Only if you have
matter sufficiently clumped together will the fluid become a superfluid and
generate the additional force. If the matter isn’t sufficiently clumped, or is
just too warm, it’ll not condense.
Again, the effect is right but the physics is
wrong. There’s no matter, but the regions of space where the postinflation
oscillations are found are scattered by the continuing expansion of the
universe, and only where this energy is sufficiently clumped together will its
gravitational force be large enough to look like dark matter. Sabine again:
This
simple idea works remarkably well to explain why the observations that we
assign to dark matter seem to fall into two categories: Those that fit better
to particle dark matter and those that fit better to modified gravity. It’s
because the dark matter is a fluid with two phases. In galaxies it’s condensed.
In galaxy clusters, most of it isn’t condensed because the average potential
isn’t deep enough. And in the early universe it’s too warm for condensation. On
scales of the solar system, finally, it doesn’t make sense to even speak of the
superfluid’s force, it would be like talking about van der Waals forces inside
a proton. The theory just isn’t applicable there.
OK there, just read “clumped” for “condensed,” and
“dark matter” for “superfluid.” Sabine again:
I was
pretty excited about this until it occurred to me there’s a problem with this
idea. The problem is that we know at least since the 170817 gravitational wave
event with an optical counterpart that gravitational waves travel to good
precision at the same speed as light. This by itself is easy to explain with
the superfluid idea: Light just doesn’t interact with the superfluid. There
could be various reasons for this, but regardless of what the reason, it’s
simple to accommodate this in the model.
The reason is that light doesn’t react with vacuum spacetime.
This has
the consequence however that light which travels through the superfluid region
of galaxies will not respond to the bulk of what we usually refer to as dark
matter. The superfluid does have mass and therefore also has a gravitational
pull. Light notices that and will bend around it. But most of the dark matter
that we infer from the motion of normal matter is a “phantom matter” or an
“impostor field”. It’s really due to the additional force from the superfluid.
And light will not respond to this. As a result, the amount of dark matter
inferred from lensing on galaxies should not match the amount of dark matter
inferred from the motion of stars.
Wrong again. Hossenfelder and Mistele didn’t
observe any significant difference in their study. There’s no phantom matter or
impostor field. However, the idea that dark matter is extra, invisible energy in
space that is clumped together in galaxies and not so much in galaxy clusters,
so its gravitational pull is stronger or weaker accordingly, is correct. And we
know what this energy is and where it comes from, even if the physicists don’t.
