*3D map of the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing with the Hubble Space Telescope.*

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Posts tagged with **dark matter**

*3D map of the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing with the Hubble Space Telescope.*

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hi-res

** The origins of mass & the feebleness of gravity** by Frank Wilczek

**tl,dr:**

@jshadlen quarks & gluons ∃ in a virtual-particle soup. The energy quanta where heisenberg locality−strongcharge balance = particle masses.

— isomorphismes (@isomorphisms) November 19, 2012

- dark matter & dark energy
- "Even though protons, neutrons, and electrons comprise only 3% of the universe’s mass as a whole, I hope you’ll agree that it’s a particularly significant part of the mass." lol
- "Just because you can say words and they make sense grammatically doesn’t mean they make sense conceptually. What does it
*mean*to talk about ‘the origin of mass’?” - "Origin of mass" is meaningless in Newtonian mechanics. It was a primitive, primary, irreducible concept.
- Conservation is the zeroth law of classical mechanics.
`F=MA`

relates the dynamical concept of force to a kinematic quantity and a conversion factor (mass).- rewriting equations and they “say” something different
- the US Army field guide for radio engineers describes “Ohm’s three laws”:
`V=IR`

,`I=V/R`

, and a third one which I’ll leave it as an exercise for you to deduce” `m=E/c²`

- Einstein’s original paper
*Does the inertia of a body depend on its energy content?*uses this ^ form - You could go back and think through Einstein’s problem (knowing the solution) in terms of free variables. In order to unite systems of equations with uncommon terms, you need a conversion factor converting
`a ∈ Sys_1`

to`b ∈ Sys_2`

. **Min 13:30**“the body and soul of QCD”- Protons and neutrons are built up from quarks that are moving around in circles, continuously being deflected by small amounts. (chaotic initial value problem)
- supercomputer development spurred forward by desire to do QCD computations
**Min 25:30**“The error bounds were quite optimistic, but the pattern was correct”- A model with two parameters that runs for years on a teraflop machine.
**Min 27:20**The**origin of mass is this**(`N≡nucleon`

in the diagram): QCD predicts that energetic-but-massless quarks & gluons should find stable equilibria around .9 GeV:

Or said alternately, the origin of mass is the balance of quark/gluon dynamics. (and we may have to revise a bit if whatever succeeds QCD makes a different suggestion…but it shouldn’t be*too*different)- OK, that was QCD Lite. But the assumptions / simplifications / idealisations make only 5% difference so we’ll still explain 90% of the reason where mass comes from.
- Computer ∋ 10^27 neutrons & protons
- The supercomputer can calculate masses, but not decays or scattering. Fragile.
**Minute 36.**quantum Yang-Mills theory, Fourier transform, and an analogy from`{ a stormcloud discharging electrical charge into its surroundings }`

to`{ a "single quark" alone in empty space would generate a shower of quark-antiquark virtual pairs in order to keep a balanced strong charge }`

**Minute 37.**but just like in QM, it “costs” (∃ a symplectic, conserved quantity that must be traded off against its complement) to localise a particle (against Heisenberg uncertainty of momentum). And here’s where the Fourier transform comes in. FT embeds a frequency=time/space=locality tradeoff at a given energy (“GDP" in economic theory). The “probability waves" or whatever—spread-out waveparticlequarkthings—couldn’t be*exactly*on top of each other, they’ll settle in some middle range of the Fourier tradeoff.- "quasi-stable compromises"
- This is similar to how the hydrogen atom gets stable in quantum mechanics. Coulomb field would like to pull the electron on top of the proton, but the quantum keeps them apart.
- "the highest form of musicality"
- Quantum mechanics uses the mathematics of musical notes (vibrating harmonics).
- Quantum chromodynamics uses the mathematics of chords, specifically triads since 3 colour forces act on each other at once.
- Particles are nothing more than stable tradeoffs that can be made between localisation costs (per energy) from QM and colour forces.
- (Aside to quote Wikipedia: “Mathematically, QCD is a non-Abeliangauge theory based on a local (gauge) symmetry group called SU(3).”)
**Minute 40.**Because the compromises can’t be evened out exactly due to quanta, there’s some leftover energy. It’s the same for a particular kind of quark-gluon interaction (again, because of the quanta). The .9 GeV overshoot | disbalance | asymmetry in some particular quark-gluon attempts to balance creates the neutrons and protons. And that’s the origin of mass.

**Minute 42. Feebleness of gravity.**

- (first of all, gravity
*is*weak—notice that a paperclip sticks to a magnet rather than falling to the floor) - (muscular forces are the result of a lot of ATP conversions and such. That just happens to be even weaker—but if you think of how far removed those biochemical electropulses and cell fibres are from the fundamental foundation, maybe that’s not so surprising.)
- Gravity is 40 orders of magnitude weaker than the electrical force. Not forty
*times*, forty*orders of magnitude*. - Planck’s vision; necessary conversion; a theory of the universe with only numbers.
- The Planck distance, even for nuclear physicists, is about 20 orders of magnitude too small.
- The clunkiness of Planck’s constants mocks dimensional analysis. “If you measure natural objects in natural units, you should get something of the order of unity”.
- "If you agree that the proton is a natural object and the Planck scale is a natural unit, you’d be off by 18 orders of magnitude".
- Suppose gravity is a primitive. Then the question becomes: “Why is the proton so light?” Which now we can answer. (see above)
- Simple physics (local interactions, basic = atomic = fundamental = primitive behaviours) should occur at Planck scales. (More complex behaviours then should “emerge” out of this reduction.)
- So that should be, in terms of energy & momentum, 10^18 proton masses, where the fundamental interactions happen.
- The value of the quark-gluon interaction at the Planck scale. “Smart” dimensional analysis says the quantum level that makes protons from the gluon-quark interactions then gets us to ½, “which I hope you’ll agree is a lot closer to unity than 10^−18”.
**Minute 57.**“A lot of what we know about the deep structure of the Standard Model is summarised on this slide”- weak force causes beta decay
- standard model not so great on neutrino masses
- SO(10)’s spinor representation has all the standard model’s symmetries as subgroups
**Minute 67.**Trips my regression-analysis circuits. Slopes & intercepts. Affine!- Supersymmetry would have changed the clouds and made everything line up real nicely. (The talk was in 2004 and this week, in 2012, the BBC reported that SuSy was kneecapped by the latest LHC evidence.)
- "If low-energy supersymmetry turns out to be false, I’ll be very disappointed and we’ll have to think of something else."

(Source: mit.tv)

Lawrence Krauss, author of *A Universe from Nothing* lecturing on **cosmology**.

- Don’t really agree with or like his monolithic straw-man representation of “religion" versus "science" at minute 6. "Religion pretends to know all the answers" .

Sub-i, sub-j, larry. There are many religions and many sciences. - Minute 14.
**Edwin Hubble’s original data!**straight-line plot through a bunch of dispersed points. “That’s why we know he was a great scientist” — nobody laughed in the tape, but I did — “he knew that he should draw a straight line through a cloud of points”. I also love it when people take the time to go through an old paper, pull things out, and present them anew. - I have never understood the business of
**standard candles**. To me it seems like you have two degrees of freedom (distance and brightness), only one of which can be knocked out by the measurement of apparent brightness.

So say we figure out a “standard candle” — a star with a particular colour signature that tells us “The star is at X phase of its life, is made up of Z, and such stars always shine at a constant brightness of 1 for Q million years.”

But still — how do we know that our theory is right? How do we*know,*know, know that it’s really brightness of 1? It’s not like we can triangulate. And it’s certainly not like we’ve been there and seen it first-hand. - I had the same problem in a discussion with a geologist a few months ago. I sometimes get the sense that working scientists are so immersed in the practical fact that, yes, for all intents and purposes we know X to be true, that they’re not willing to step back to an abstract, philosophical level and say: “Well, if you really keep pulling on the threads, there are assumptions at the bottom of everything, so yes, we really don’t
*absolutely know*X to be the case. However, Philosophical Prig, we don’t*really know*we’re not living in The Matrix either! So hush up and get back to doing something relevant.” But that’s the kind of answer I really want to hear: no, we don’t know know know, but for all practical purposes, yes we know. - Minute 15.
**How old is the universe?**So Hubble got the answer wrong in 1929, and it was obviously wrong. “Scientists don’t know what they’re doing”

But I had the same reaction to people talking about dark matter in the 90’s. “What is this*stuff*we call dark matter? Or dark energy?” As I understood it at the time, “dark matter” just represented a 90% fudge factor in astronomical measurements. It could be that gravity or quarks or anything else about the laws of physics is simply different in other parts of the universe. And how would we rule out that hypothesis? We just rule it out by assuming that the laws of Nature are the same everywhere, because that’s what we’ve assumed for the last few hundred years and it’s always worked out. Straight-line extrapolation to “That assumption must be true now and everywhere” despite that we’re now talking about multiple galax*ies*so unimaginably far away. - Minute 18:30
**"This is a Hubble plot, much better than Hubble’s plot. It was made after the discovery that on a log-log plot, everything is a straight line.”**Again, no laughs, but I thought that was hilarious. - Calculations that estimate the
**total energy in all vacuums**add up to 10^28 times the observed mass of the universe. Whoops. **Dark matter**here on Earth? Let’s go down into the mines and measure it. (By the way, where would the physicists be if those evil resource-extraction companies in Lead, South Dakota hadn’t negotiated with the legal entities that be and drilled into the Earth’s crust? Way to play it as it lies, Sandia Labs. #scruples)- Flat, closed, or open universe? (also why are these the only three options?) Well, we only observe 30% of the mass thta would be required to make the universe flat.
- A gigantic, gigantic, um, really gigantic triangle — to measure the curvature of the universe.
- That’s what those microwave-background radiation detecting
**balloons in Antarctica**have been doing. - There’s always something there, even when there’s nothing. (see this video of the quantum fields flickering about in empty space)
- 90% of the mass of a proton is due to the vacuum. (not delta spikes, more like 1/x or
`exp(−x)`

integrals.) Therefore**your mass is 90% due to quantum fluctuations around the zero point energy.** - The universe also has a net total energy of 0. Hence the possibility of “a universe from nothing” (our universe needn’t have a Creator since there is enough mass/energy in the physical vacuum that those virtual fluctuations could have acted as a Prime Mover).
- 70% + 30% = 100%
- Making our place in the Universe even less special. “Regular” matter—the stuff we observe—is only a 1%
in the uniform dark-energy / dark-matter background of the universe.**pollution** - Deep-future scientists (like in a few billion years) won’t be able to observe other galaxies. Measuring the universe, they will observe (correctly) that their galaxy is the only one around, and that there is nothing but empty, eternal space around them.
- So they will be “Lonely and ignorant, but dominant. Of course those of us who live in the United States are already used to that.”