Possible interaction between baryons and dark-matter particles revealed
nature.com
nature.com
Being the skeptic I am, I suspect that it's more likely that there is some systematic error that is being underestimated or overlooked rather than new physics. Fortunately the experiment is simple enough that it can be reproduced elsewhere relatively easily.
Interestingly, the region around 75 MHz is between two ITU broadcasting allocations. They claim to rule out the FM band as the source of the higher spectral edge through several possible channels, but I wouldn't be surprised if there was some way to get excess power in those bands in some way they hadn't considered (although I guess any strange propagation mechanisms would probably be time-dependent).
http://www.preposterousuniverse.com/blog/2018/02/28/dark-mat...
I am wondering, can't there be something like gravitational cooling? When playing around with gravitation simulators one observes that sometimes high velocity parts leave the bulk, which in my understanding leads to a cool down of the pack (the escaping part carries away kinetic energy, after all). If I let some "cool" matter interact with "hot" matter only gravitationally, I'd expect that this leads to an equal "temperature" eventually. Is it, that due to the very weak interaction, time scales are too long for this?
The period between recombination and "first light" from the first stars (triggering reionization) is not especially well understood, but the expectation is that the expansion of the universe would be pretty smooth in that epoch. So the neutral hydrogen around the time of first light being cold enough to produce the unexpectedly strong 21cm absorption line is an oddity.
If evidence holds up suggesting that this gas is uniformly colder than expected then we could take the position that our idea of the history of the expansion is somehow wrong, or alternatively that some other process was at work at the end of the dark ages. We have constraints on both; and in particular "some other process" is tricky because the almost-exactly-black-body spectrum of the CMB puts constraints on early cooling-by-clumping (where cooling is up to "chemistry", where that's a(n exothermic, in this case) reaction between particles of different species).
There could be "chemistry" in the dark matter sector that allows dark matter to cool by extremely local clumping (for example, if in the "dark ages" before recombination there are two oppositely-charged dark matter particles and at recombination they combine into one neutral dark matter composite particle, analogously to how electrons and protons recombined into neutral hydrogen), but then you have to figure out how to have the dark matter be colder than the hydrogen and how to thermalize the hydrogen to the dark matter. You also have to avoid smearing out small matter density fluctuations.
If structure formation works the way we think, everything at recombination seems too uniform and diffuse for local gravitational interactions to do the job of transferring much momentum from the matter sector to the dark matter sector in time for the 21 cm absorption line seen by EDGES. There are also constraints on extra long-range interactions, so Carroll's raising the idea of a zero-mass boson mediating the interaction is hard to imagine (a massive mediator would be shorter-range, in general, and could carry more momentum between matter and dark matter, but there are constraints on such interactions from the much later universe -- for instance, we would expect missing momentum in particle physics experiments, along the lines of the missing momentum that led to the discovery of the neutrino).
The problem is that there are lots of strongly correlated observations and pushing at one tends to cause problems with one or more of the others. But that's what theorists in this area (model building) seem to like to do. :-)
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[1] Peter Coles (cosmology, Cardiff) has a good, accessible write-up from some years ago, adapted here: https://ned.ipac.caltech.edu/level5/Glossary/Essay_lss.html
[2] https://en.wikipedia.org/wiki/Horizon_problem?oldformat=true
In that case, if the DM and matter can only interact gravitationally (and DM-DM interactions are also gravitational), then you have a dance wherein the collisional normal matter sheds momentum via radiation, letting the normal matter fall into the DM eventually. The momentum exchanged between the DM and the normal matter will be pretty small.
(This is similar to what people pursuing the cosmic web hypothesis try to model, essentially, and is what's conjectured to be happening during the dark ages).
ETA: the key thing here is that the collisionless cold dark matter will stay cold, while the normal matter will get much hotter (and light up normal matter further away still). Isn't this the nub of the EDGES result?
If you arrange the matter galaxy so that its internal structure is sufficiently stable then the whole binary system would lose momentum-energy to gravitational radiation. It won't be much, and that's a big "if" (and the "if" also works against trying to see the matter galaxy cool, especially as the energy loss would tend to contract the "bar").
It seeks to examine gravitatonal waves shed by a 2-galaxy cluster.
"pessimistic point of view justified by the combination of great numerical difficulties (three-dimensional calculations) together with very disappointing small values expected for the gravitational-wave luminosity, the amplitude, etc"
"In brief, our simulated cluster produces changes in the relative distance of the order of 10-22—detectable with current technology—in a short period of 4 days."
(LIGO 2015 was about the same relative length change (h), but with a frequency of 35 - 250 Hz. I'm not sure how catching part of a gravitational wave of ~ 10^-17 Hz could be caught by a LIGO-like detector, since only higher derivatives of h are useful for identifying gravitational radiation).
http://iopscience.iop.org/article/10.1086/311446/fulltext/98...
(but of course for cooling we're more interested in the luminosity, which is small compared to that of an ordinary galaxy, but a bit more interesting compared to the blackbody radiation of a galactic-mass diffuse cloud of atomic hydrogen, although that's only considering the normal-matter member of the binary, rather than the total energy leaving the region of spacetime the binary is in.)
Also, if you let the hot and cold clouds fall into each other, then electromagnetic scattering will do the bulk of the work of thermalization (or more likely the heating of both clouds of inelastically colliding matter; cf. collisonless dark matter clouds sliding through one another).
I see a low res 2d picture and apparently they see cold particles that are around 3x the mass of protons and the structure of the universe.. kinda nuts..
Thinking of things in terms of math in order to solve problems is intrinsically creative :). I'd agree there is nothing mystical about creativity or mathematics, though.
In the end I loved (pure) maths more than philosophy so graduated with Theoretical Physics and Mathematics. There were probably a quarter of the physics students doing the Philosophy of Science module (the only things I remember covering were Aethers, Xeno's Paradox, maybe also the Realism of QM Interpretations [it was a couple of decades ago]).
First I want to make an observation. Do you know the history of how the study of complex algebra/calculus came about? If so, I assume you will agree that it was initially a completely abstract thought experiment with no connection to anything in the “real” world.
Given your assertion that math is without meaning, it would seem to me that mathematical ideas that originate purely out of human imagination would just be arbitrary semantics.
Then how can it be that complex analysis only several decades after it was formulated turned out to be not only useful, but necessary to formulate the theory of quantum mechanics in a way that agrees with physical observation?
I can name numerous other examples of the same phenomenon; namely that a purely abstract mathematical idea is long after its formulation shown to be profoundly reflected in physical reality.
To me it seems obvious that the way these phenomena occur implies that part of the process by which humans use their imagination and reasoning to come up with abstract mathematical ideas, is more akin to using their intuition to map out objective ‘structures’ of logic (that are also reflected in the underlying structure of physical reality) than to simply play with semantics, as it seems you are asserting.
Tl;dr Post modernist philosophers are fools and they should be ashamed. Qed
Thanks for biting =)
I agree that the symbolic language we call mathematics and reality are not one-to-one as you say. But the fact that we can use abstract reasoning around these symbols to uncover new ways of understanding of the physical world, especially in cases like the one I lined out in my example, implies to me that there must be some objective reality that is in some way captured by these symbols, in a way that plain philosophy cannot.
Personally I subscribe to Roger Penrose's lines of thought on these matters: http://theeternaluniverse.blogspot.no/2012/09/penrose-on-whe...
So to answer your question, I agree that math is a tool, but I think in some sense it also more than a tool. I believe it can also be seen as a map into a platonic reality, and that there is some element of our mind that is able to observe this realm which allows us to draw the map (using mathematical symbolic language) and come to an agreement about how it should be drawn. And that elements of this platonic realm are for some mysterious reason also reflected in the structure of our physical reality.
A close friend of mine refers to humans as "symbol makers" and I hold firmly that everything in the flow of life is meaningful, but it's really astounding that we can filter out useful patterns from our surroundings. Your point alludes to me in a similar way the beauty of a leaf or a tree: it's been speculated and suggested that over many millennia our sensory systems (namely sight) have tuned in and honed in on being able to find tasty ripe fruits and berries (why they may appear red and bright or purple and bright when in full ripeness and before ruin .. to pilfer an Alt-J lyric).
In that way, perhaps maths is some sort of tree or leaf or forest that is naturally existent, not actually separate from the earth or the forest or the consciousness of man, but still somehow a useful set of patterns our [mind] intellect-sense has been able to pick out and find the tasty and juicy bits of.
One very fascinating part of the whole narrative of mathematics is Progress. For example, Kepler and his assistant's calculated observations of the planets, mathematicians dedicating their lives to figuring out n-many decimal places of logarithms and creating reference books, and also equations and derivations. Although maths may somehow "exist" naturally because a set of equations or a set of inferences or physical phenomena may have a mathematical representation, they still need to be discovered (and often re-discovered) to stick around and be of any use to us. To me it still echoes of the personal mission of understanding and critical thinking -- one must come to the solution on their own and verify it in their personal experience to truly feel it and know it to be truthful.
Would you categorize maths as more of an invention or as a discovery? Pure discovery would imply that maths exists on its own like a tree does (or "might" if we consider that a perceiving consciousness must also be part of the 'tree'). Whereas, an invention is something deliberately put together to solve a functional need in the life of man.
Maybe in the sense the Von Braun solved rocketry. I agree that everything that has come since have been refinements to Nietzsche's developments (dare I say models) but those refinements have brought about the real-world application of philosophy more than Nietzsche ever did.
See Mao, or Popper, or even though I can't stand the guy Chomsky.
I wasn't aware that philosophy was a problem for which a "solution" could be found?
I'm not sure I agree that solving a lot of the then/now "problems" with philosophy is the same as solving the entire field of philosophy. Especially since it requires mobile goalposts.
Also, it's a hilarious and an absurd claim "x Solved Philosophy" because that's like saying "Tony Hawk solved the skateboard." Perhaps Tony Hawk is great at skateboarding, but you can never personally know what it's like until you try yourself. Philosophy is not something that can be solved by someone outside of yourself, not even Nietzsche can wipe away your ignorance, only you can do that for yourself.
No. I suppose when you say "nothing" you're talking about philosophical propositions, which can be mapped to computer programs. In which case we can note that (1) the vast majority of programs have never been generated before by any process and (2) the vast majority of possible programs cannot be reduced to simpler programs that might have been expressed earlier.
https://en.wikipedia.org/wiki/Kolmogorov_complexity https://en.wikipedia.org/wiki/Algorithmically_random_sequenc...
In particular, this new observation constrains the nature of dark matter (lower particle mass than expected and "highly non-relativistic").
Dark energy is the "why is the universe expanding so fast"-stuff and dark matter is the "why are galaxies so heavy"-stuff of the universe.
Galaxies appear to be heavier than what you get by adding up all the visible mass (you can tell by how much a galaxy bends light coming from behind it), so it makes sense to talk about matter. It's dark because it doesn't seem to interact electromagnetically with ordinary matter.
Looking at just all the gravity (dark or not) in the universe you'd expect all the matter in the universe to slowly start clumping together, or at least slow down the expansion of the universe, but we find that things are flying apart, and increasingly quickly so. So there's some force at play, and that's dark energy.
edit: letters
https://www.nature.com/articles/d41586-018-02616-8
It's more about the light from the first stars but it explains why the signal hints to light and cool dark matter.
http://www.watoday.com.au/national/western-australia/antenna...
[1] https://arstechnica.com/science/2018/02/signal-of-the-univer...
laying immaginary tiles upon immaginary tiles