121–130 of 131 posts
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Thank you! 2.5% of the universe's missing matter has been found.
Not 2.5% of the missing matter. 2.5% of the matter.
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> Not sure who you're referring to. These results are completely consistent with the standard model of cosmology. Not if what is being detected is simply mass associated with filamentary currents of energy (with attendant magnetic fields) rather than particular particles.
They're modelling filaments as cylindrical tubes of hot electrons connecting pairs of galaxies. I don't know what you mean by "mass associated with filamentary currents of energy", but while the electrons are hot (~million Kelvin), they're non-relativistic and their kinetic energy is negligible.
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Can you please give any usable link for this: > What does not match observation extremely well is naive quintessence models where the metric expansion works within galaxies and is simply checked by the gravitational interactions of the matter within them Or write some additional details about it. I know that the "popular" explanations claim that "everything" expands, and I understood from your reply that what we see…
> "usable link" How much technical detail do you want? Starting with the "gimme hardcore!" end, I was thinking of how to construct an argument using vierbiens and then how to boil it down to something accessible (or at least representable on LaTeX-free HN), and then remembered that it had already been done by Cooperstock et al.: http://xxx.lanl.gov/abs/astro-ph/9803097 The tl;dr is that if the cosmological expansion…
(To anybody who's also interested, I've found the thesis by Elise Jennings here: http://etheses.dur.ac.uk/616/ )
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An implicit assumption is that the universe is isotropic and homogenous at that scale. Meaning, it looks the same from any point and any direction. So you might not detect photons in one particular direction, but we should assume that they should be going in all directions. Otherwise that theory is just moving the goal from "where's this energy" to "why is it pointing towards that". CMB is consistent with, every dire…
But isn't it a hell of a lot less of a stretch to imagine there are more photons in other parts of the universe than here, than to imagine there is some sort of mysterious dark matter permeating all of the universe? If we're going to be unable to interact with whatever dark matter is to test may hypothesis, we might as well propose the hypothesis that requires the least radical changes to our fundamental theories of…
However there's this one experiment that says the answer is `Energy = 42`. `f(x)` is still useful, everything else works.
We can just amend the equation to be: `Energy = Mass + Photons + DarkMatter` where `DarkMatter = -42` and `f(DarkMatter) = 0`.
Or we can keep the E=M+P but change the way f works to be: `f(Photons, X) = Y` where for almost any value `f(Photons, X') = 0` and in this one case `f(Photons, X") = 42`.
To me it's clear that the first approach is less complicated. The first approach raises one question, "why -42?" The second approach raises "why does X?" exist and "why 42?"
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By the way, you are mistaken, we do interact with Dark Matter, that's how we detected it (Bullet Cluster). Gravity does interact with it.
"made of particles called baryons rather than dark matter" That's clumsily worded, as it makes it sound like it's still something exotic. _We're_ made of baryons: this is just normal matter.
As a former physics student, I see your point but disagree. Apologies for the wall of text about just this one choice of wording, but discussing why science communication is a very difficult trade-off takes a bit of space. One reason to stick to "baryons" is that it is the term used by the researchers in their papers. So it is more true to the research that is being summarised. The start of the article (unlike its ti…
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Photons lack mass right?
not exactly. As photons are constantly moving at the speed of light (citing the theory of relativity I don't really understand) they have no resting mass . But they have an impuls and create a force of impact (used in sun sails) from which a theoretical notion of ... mass (kinetic, perhaps?) can be derived. I'd like to know how it's derived originally, too though. edit: if E=mc² with E(photon)=f•h and f=c/λ, then m=h…
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not exactly. As photons are constantly moving at the speed of light (citing the theory of relativity I don't really understand) they have no resting mass . But they have an impuls and create a force of impact (used in sun sails) from which a theoretical notion of ... mass (kinetic, perhaps?) can be derived. I'd like to know how it's derived originally, too though. edit: if E=mc² with E(photon)=f•h and f=c/λ, then m=h…
Normally when discussing mass, people are referring to resting mass, not relativistic mass.
Can I just check - my understanding is that we can only see 5% of the expected mass in the universe - so we have just found another 5%? meaning dark matter needs to account for 90%? plus, how awesomely beautiful is the idea of tendrils of has connecting the galaxies through space.
Tendrils between galaxies is mind-blowing. Aren't galaxies very very far apart? And there is basically nothing in between? How are subatomic particles - baryons - able to survive the constant expansion? Do the tendrils keep getting thinner? Can they be a medium to transmit intergalactic information someday?
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Normally when discussing mass, people are referring to resting mass, not relativistic mass.
normally, people don't discuss mass. rather they are simply heavy. most don't even really care why. and those who do, conflate the idea with weight often enough.