Sunday, May 15, 2016

Comments of the Week #110: from dark matter and black holes to supernovae and dark energy

Comments of the Week #110: from dark matter and black holes to supernovae and dark energy:

“If I can’t make it through one door, I’ll go through another door – or I’ll make a door. Something terrific will come no matter how dark the present.” -Rabindranath Tagore
Time continues marching on here at Starts With A Bang, just as it does everywhere. My Patreon supporters have stepped up their game, and we’re just $21 shy of unlocking our next goal! There are two great new items this week I’d love to share with you: first, our newest Podcast on dark energy and the fate of the Universe,

and second, a video whose script I helped write (with a bonus coming up) for Kurzgesagt – In a Nutshell, who make some of the best science videos I’ve ever seen:


We’ve also produced a fine suite of articles this week, and here’s a look back at them all:


For those of you in Washington State, head on over to Centralia College on May 20th at noon, where I’ll be speaking on Fate of the Universe. (And autographing books, too!) Now let’s jump on in to the best of the second week in May, and dive into our Comments Of The Week!



Image credit: NCEP CFSR 1981-2010 Climatology / Ryan N. Maue / WeatherBELL.


Image credit: NCEP CFSR 1981-2010 Climatology / Ryan N. Maue / WeatherBELL.
From Apeon LastnmUnk on the concept of settled science: “Your description of science as continually seeking, and never being absolute, refutes the “Settled Science” of Global Warming.”
By that logic, the attributes of continually seeking and never being absolute would refute any scientific conclusions one would ever make. See if you can follow this train:

  • Science accumulates large amounts of data through experiment, measurement and observation: a suite of evidence.
  • In that suite of evidence are uncertainties: uncertainties in the measurements/observations themselves and uncertainties about what results other experiments-not-performed and observations-not-made would yield.
  • And then, to explain it all, we have scientific theories that are valid over a certain range, with a certain degree of confidence we can express.
The Global Warming theory — that the Earth is warming and that human-caused changes to the atmosphere is the culprit — has been quantified to be valid at approximately 4.8-sigma statistical significance: to a 99.999%+ probability. Yes, there are more things to understand about it, but my description is not a refutation, unless you’re being completely dishonest about what science is and isn’t.



Image credit: Rutgers, retrieved from http://www.physics.rutgers.edu/~zrwan/physics/.


Image credit: Rutgers, retrieved from http://www.physics.rutgers.edu/~zrwan/physics/.
From Sinisa Lazarek on the Stern-Gerlach experiments: “Concerning entanglement: “So what if you took the ones you measured to be +ħ/2 in the x-direction, then measured the y-direction …. ”

Because you simply CAN’T do that in real life. Once you made ONE measurement, that’s it… game over. No more entangled pair.

You can entangle them again, but this is a completely new [measurement], absolutely unconnected to the one you did before, in all practical sense.. they are new particle pairs.”
I think there has been a misunderstanding here. The Stern-Gerlach experiment isn’t about entanglement, it’s about quantum indeterminism and the nature of quantum systems. If you have a spin-ħ/2 particle, it will have a spin along the x-axis that’s either +ħ/2 or -ħ/2, right? Same with the y-axis and the z-axis. It’s all in an indeterminate state, until you measure it.

Yet if you measure the spin in the x-direction and get, say, +ħ/2, you destroy all the information about the y-axis and z-axis directions. They now have 50/50 shots of being +ħ/2 and -ħ/2. If you then measure the y-axis spin and get -ħ/2, the x-direction is now re-randomized, and has a 50/50 shot of being +ħ/2 and -ħ/2. That’s the point of Stern-Gerlach; nothing to do with entanglement.

From See Noevo on flippancy: “Welcome to the SciFi Channel.”
Here’s a quote for you that I think applies: “Don’t waste your time trying to explain yourself to people that are committed to misunderstanding you.” You clearly have all the answers you want or need, so there’s no need for me to provide anything further to you, right?



The giant elliptical galaxy, M87, and its 5,000+ light year-long jet, highly collimated, as imaged by the Hubble Space Telescope. Image credit: NASA and The Hubble Heritage Team (STScI/AURA).


The giant elliptical galaxy, M87, and its 5,000+ light year-long jet, highly collimated, as imaged by the Hubble Space Telescope. Image credit: NASA and The Hubble Heritage Team (STScI/AURA).
From Denier on black hole jets and their cause: “How is the inability to discern the electric charge of the matter that makes up a black hole reconciled with the jets emanating from the poles of feeding black holes? As I understand the theory, the particles in the jets are accelerated by the magnetic field of the black hole. The magnetic field should vary with the make-up of the black hole, no?”
This is actually a hotly debated topic! There certainly are magnetic fields accelerating charged particles here, and that’s what causes the jets. But are these magnetic fields:

  1. Relics of the magnetic fields that existed in the stellar core/neutron star that existed before a black hole formed, remaining due to a process like flux pinning?
  2. A fundamental property of a charged black hole that’s rotating?
  3. Due to electric currents from outside the black hole’s event horizon, due to the accretion disk or other matter outside it?


Image credit: ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al. (microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray).


Image credit: ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al. (microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray).
Of these three options, number 2 is the least favored explanation, as a galaxy like Centaurus A (above) has only a 55 million solar mass black hole; just 13 times as massive as our own. It’s unlikely that such a large electric charge differential will exist in the black hole; what would segregate billions of Coulombs’ worth of charge, keeping ~10^30 extra charges of one type inside the black hole while expelling that amount outside of it? The numbers seem too great to be explained by that possibility, but we have been surprised before.



The Hubble eXtreme Deep Field (XDF), which revealed approximately 50% more galaxies-per-square-degree than the previous Ultra-Deep Field. Image credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team.


The Hubble eXtreme Deep Field (XDF), which revealed approximately 50% more galaxies-per-square-degree than the previous Ultra-Deep Field. Image credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team.
From Naked Bunny with a Whip on the vastness of the Hubble eXtreme Deep Field: “Photos like this make me glad I’m so ill-equipped to fathom the vastness on display. I think it’d be overwhelming if I could even approach it.”
Personally, I can’t wait for the James Webb Space Telescope to push these limits back even farther. Is 170 billion galaxies in the observable Universe the right number? Certainly not; it’s surely too low. But by how much? Is the number more like 300 billion? 1 trillion? 100 trillion? And where is the cutoff for what we consider a galaxy: 1% the mass of our Milky Way? 0.1%? 0.001%?

These are questions that we’ll actually have quantifiable answers to over the next generation. It may bend your mind, but it should bend your mind!



The exoplanet Kepler-452b (R), as compared with Earth (L), a possible candidate for Earth 2.0. Image credit: Image credit: NASA/Ames/JPL-Caltech/T. Pyle


The exoplanet Kepler-452b (R), as compared with Earth (L), a possible candidate for Earth 2.0. Image credit: Image credit: NASA/Ames/JPL-Caltech/T. Pyle.
From eric on the exoplanet problem: “This seems a big step to me. AIUI our atmosphere is a result of the particular evolutionary pathway that life took on Earth. Specifically, we have an oxygen rich atmosphere with few sulfides, carbonates, nitrides, etc. because (we think) the earliest forms of life ate the latter and pumped out oxygen as a waste product. If Gould is right and rewinding the tape of life couldn’t be expected to lead to a similar end-state, then there is very little reason to believe that a different rocky planet in a habitable zone with life would develop atmospheric conditions similar to ours.”
It is a big step, but I don’t think it’s necessarily as big a step as you fear. It’s a question of biochemistry, but a relatively simple one: if you’re living in a methane-rich (carbon), ammonia-rich (nitrogen), and water-rich environment (oxygen), what are the good, possible pathways to construct molecules that allow you to gather, store, and harness energy? It turns out a considerable number of successful pathways result in the production of molecular oxygen as a waste product, and hence would severely enrich the atmosphere.

You don’t need a similar end-state to get some similar generic properties, and an oxygen-rich atmosphere may be one of those properties. We’re not sure, as it’s pretty hard to extrapolate probabilities from an N=1 sample size, but certainly examining habitable-zone exoatmospheres will teach us a lot about what’s out there!



Artist’s depiction of the worlds found by Kepler thus far. Image credit: NASA/W. Stenzel.


Artist’s depiction of the worlds found by Kepler thus far. Image credit: NASA/W. Stenzel.
From Sinisa Lazarek on an objection to 60 billion habitable-zone super-Earth-or-smaller planets in our galaxy: “If of the 150.000 sampled stars, we found 2.000 exoplanets, of which 40% are rocky… that would mean (to round it).. 1000 rocky planets for 150.000 stars, or in other words.. a little less then 1% of the numbers of stars. How can then we have 60 billion estimated habitable worlds in our galaxy, if our galaxy has 100 billion stars. By math above, we should less then 1 billion rocky worlds.. of which some would be in habitable zone. In other words.. in millions.. but not in billions. One order of magnitude lower.

I’m either missing something important, or there’s a mistake somewhere in numbers.”
Which is a good objection; you should be able to run the math for yourself. But this was answered in spirit very well by Denier: “Kepler is finding exoplanets via the transit method which means the orbital plane of the solar system has to be inline enough for Kepler’s cameras to see the planet cross the face of the star. Your back-of-the-napkin calculations left out the odds of that alignment.”

The odds of a good alignment are significantly higher for very close-in planets, and are actually <1% by time you get out to a star’s habitable zone. So that accounts for more than two orders of magnitude in your back-of-the-napkin calculation, and the fact that our galaxy has more like 400 billion stars than 100 billion and that finding inner planets likely means there are many more, outer planets greatly changes the estimates.



The 21 Kepler planets discovered in the habitable zones of their stars, no larger than twice the Earth's diameter. Image credit: NASA Ames/N. Batalha and W. Stenzel.


The 21 Kepler planets discovered in the habitable zones of their stars, no larger than twice the Earth’s diameter. Image credit: NASA Ames/N. Batalha and W. Stenzel.
From Denier on tidal locking and what that means for exo-life: “A big concern, and something I didn’t see addressed in the article was tidal locking. Even if you do get a planet the right size, made from the right stuff, and the correct distance from the star to support liquid water on the surface, if it is tidally locked it is not going to be Earth 2.0.”
First off, I should clarify that “Earth 2.0” doesn’t necessarily mean a planet exactly like Earth, but rather one that has complex life on its surface and that also isn’t totally inhospitable to humans. This could, however, look very different than Earth does. Yes, it’s true that most rocky planets the size of Earth or smaller in the habitable zone of an M-dwarf would probably be locked after ~5 billion years, a calculation you can do yourself.

But that doesn’t mean:

  • You can’t have life thriving in a “ring” on the border between night and day.
  • You can’t have a strong atmosphere that transports heat and energy evenly around the planet (Venus does, for instance).
  • Or you can’t have “day side” life that thrives that simply looks different from the life we know.
It might not look like Earth 1.0, but it might still be a great Earth 2.0 candidate.



Image credit: Nicolle Rager Fuller of the NSF.


Image credit: Nicolle Rager Fuller of the NSF.
From Michael Kelsey on supernova nucleosynthesis: “Theoretically, how confident are you that the r-process (i.e. single neutron capture) can really produce trans-plutonian elements? Most of the decay channels for those (man-made) elements are alpha decays, not betas. I couldn’t find (in my cursory search) papers to support your statement; any chance you can point me to a decent review?”
First off, let me be very clear about three facts:

  1. This is an active field of research where theoretical developments are far ahead of observational constraints.
  2. It is also not my primary field of study; I know about it tangentially, not from my own research.
  3. But there are good theoretical reasons why there should be some r-process production, even though the greatest abundance of these trans-uranic (or trans-plutonic, which I think is the right word) elements should be created in neutron-star mergers.


Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. Image credit: Dana Berry, SkyWorks Digital, Inc.


Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. Image credit: Dana Berry, SkyWorks Digital, Inc.
The expectation is that the supernova neutron flux — which is intense, at ~10^22 neutrons/cm^2/s — should result in neutron capture rates of ~1 neutron-per-minute, give or take. Now, supernovae are fast processes, but neutrons stick around for some time, and there’s going to be a probability distribution function that gives non-zero realizations, in a typical supernova, for the capture of up to ~20-30 neutrons by an initial (let’s say) uranium nucleus. Get up to U-239, U-241 or U-242 and you make neptunium in minutes, which makes plutonium in minutes as well. There is some considerable evidence that primordial Pu-244 exists on Earth.

If you make either Pu-243 or Pu-245 or higher, it beta decays as well, creating Americium, almost all of which — at those masses — will beta decay into curium, which has some isotopes that are quite stable! Cm-247 lives for ~16 million years on average, which isn’t enough that any of it is found on Earth, but perhaps there was some when life first arose on our planet. By looking at half-lives and preferred decay pathways, neutron capture should be able to get you all the way up the actinide chain and even into elements like 104-through-106, although probably not further than that. You asked for some reviews, and I don’t know that this will sate you, but here are a few papers you might consider if you’re interested in further reading:

There is a good discussion of some of these points further down in the comment thread from Michael and eric, but I wanted to weigh in for everyone to follow, too.



Image credit: Philipp Dettmer.


Image credit: Philipp Dettmer.
From rev on some Forbes-and-Ethan bashing: “@Ethan: Still on forbes? I don’t understand. Something is rotten in the state of Science.”
They pay me to write for them. If you’d rather pay me instead, perhaps I’ll write where you choose?



Image credit: E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL.


Image credit: E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL.
From Claud Owens on the edge of the Universe: “Let us say that we finally reach the outer limit of the universe. What should we call that on the other side of the limit?”
First off, you can’t, not unless you poke a hole in the fabric of spacetime and come out in a special-relativity-violating location. The limits of what we can reach are about 1/3 of the way to the edge of the visible Universe. If you could magically transport yourself — via wormhole or somesuch method — to the outer limit of the observable Universe, you’d simply find more Universe that was like our own on large scales and different in detail on small ones. You’d call it “Universe”, but to someone who couldn’t see it, we might (depending on our definitions) call it part of the multiverse.



Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during inflation, giving rise to imperfections in both density and gravitational waves. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research.


Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during inflation, giving rise to imperfections in both density and gravitational waves. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research.
From Jose Pacheco on the Hot Big Bang: “The Big Bang Theory doesn’t say the universe came from nothing. It says that if we rewind the universe to a point about 13.8 billion years ago, the entirety of the universe was very close together. There is a point though, where current physics break down, and we don’t know what came before.”
This is very good, although we have some very, very strong evidence that cosmological inflation came before you reach the breakdown point. You can read about cosmic inflation’s six predictions, five of which have been verified. (That’s pretty good!)



A Type Ia supernova in the nearby galaxy M82. This one is fundamentally different from the one atop this page, observed in 2011 in M101. Image credit: NASA/Swift/P. Brown, TAMU.


A Type Ia supernova in the nearby galaxy M82. This one is fundamentally different from the one atop this page, observed in 2011 in M101. Image credit: NASA/Swift/P. Brown, TAMU.
And finally, from Michael Richmond on the supernova/dark energy conundrum: “Ethan, could you please provide references for statements like “a 2015 study put forth a possibility that many scientists dreaded?” I read the article on Forbes, and I couldn’t find the reference there, either.”
Although EpiPete provided the links in a comment and the “a 2015 study showed another possibility” actually links to the press release from the Forbes article to the U. of A. piece, I thought I’d take the opportunity to discuss what the difference between the supernovae are and why it doesn’t wreck the accelerating Universe. What Peter A. Milne’s study found is that there are actually two classes of type Ia supernovae: some are “bluer” and some are “redder”. The bluer type are the minority nearby, where most of them are red, but are the majority type at great cosmic distances, where fewer are red. Therefore, there’s a bit of a bias to the data. However, as Milne says:

“To be clear, this research does not suggest that there is no acceleration, just that there might be less of it.”
You will notice that earlier dark energy reports had ~72-76% of the Universe’s energy in the form of dark energy, while more recent ones have it at ~66-68%. The Universe is still accelerating, dark energy is still a cosmological constant, and it’s still dominating the energy density of the Universe. There’s just a few percent less of it than we thought!

Have a great week, and thanks for all your support! See you back tomorrow for even more of the Universe!