Comments of the Week #160: From the edge of the Universe to the first-ever nebula [Starts With A Bang]

“You cannot hope to build a better world without improving the individuals. To that end, each of us must work for his own improvement and, at the same time, share a general responsibility for all humanity, our particular duty being to aid those to whom we think we can be most useful.” -Marie Curie

There’s nothing like looking into the deepest mysteries the Universe has to offer, and trying to come up with the explanation and understanding we can based on all the available data. That’s what we’re all about here at Starts With A Bang! It’s less than two weeks until my talk at the May 24th event: Astronomy On Tap, at Peddler Brewing Company! Join me if you can, and I promise it’ll be a great time as far as making you wonder about the Universe goes! There’s a lot coming up, but don’t forget to look back at what we’ve covered in this past week:

• How far is the edge of the Universe from the farthest galaxy? (for Ask Ethan),
• Hubble views the final frontier for dark matter (for Mostly Mute Monday),
• The scientific truth about Planet Nine, so far,
• 5 reasons why the 21st century will be the best one ever for astrophysics,
• What if cosmic inflation is wrong?, and
• Spectacular new Crab Nebula images close in on its final secrets.

As always, there’s more science than we’re able to talk about, so let’s see what extra things you can draw out as we jump into this latest edition of our comments of the week! Let’s start with our ongoing conversations from last week…

Roy Spencer’s data, from Denier’s link.

From Denier on what to do (or not do) about climate change: “perhaps the political action taking place is the correct action given *ALL* of the available knowledge (economic, societal, and physical science).
[…]
“However it is a problem that is solving itself for all the reasons I laid out which you apparently couldn’t find issue with.”
[…]
“Dr. Roy Spencer *DOES* believe the Earth’s climate is getting warmer. The particular label he’s been slapped with is a ‘lukewarmer’.”
[…]
“I certainly didn’t personally attack the man the way you just did Dr. Roy Spencer.”

You have painted an incorrect picture in many ways. First, you are incorrect about the physical science, and Roy Spencer’s role in accepting it, and the indications of Roy Spencer’s data. In 1990, Roy Spencer published results showing no warming in the upper atmosphere from the UAH dataset. It disagreed with all predictions and with other measurements. The overwhelming majority of climate scientists claimed there must be something wrong with his calibrations. He responded by, for the next 24 years, impugning them as irresponsible, bad scientists, and making claims that the true warming due to human effects is negligible. You can find some sources on this here, here and here. He claimed, as the graph you presented (above) shows, that the upper atmosphere isn’t appreciably warming, and therefore an anthropogenic cause to global warming is disfavored.

Then, in 2014, the truth came out: Spencer’s UAH team had made a huge mistake in the calibration of their data. Instead of negligible upper-atmosphere warming, they found that the upper atmosphere had been warming at +0.14 degrees per decade, double the 1880-2014 rate of 0.07 degrees per decade. Spencer’s response has been to go from outright denial to mere misinformer. Why are you showing the incorrectly calibrated data as “proof” of your claims? My theory is that you are wrong on the science and you know it, yet you refuse to change your conclusions because you do not like their implications. So what about about “the political action taking place?” There is none. There is nothing regulating carbon dioxide in the United States, period. There are proposals, all of which would be better than the “none” in place, including:

• cap and trade (the worst option, IMO),
• a carbon tax (i.e., putting a price on carbon), heralded as a free-market solution to climate change,
• or the carbon fee and dividend policy.

I think even the worst option of these would be better than the current do-nothing policy, which includes subsidies and incentives for carbon polluters. The problems are not solving themselves. You have not presented alternative numbers to the ones I gave, you merely made sweeping and unsupported statements. Global CO2 rates will not go down without tremendous technological breakthroughs or legislation penalizing CO2 emissions. Population will trend upwards and plateau at the century’s end according to all projections, landing at 10-12 billion people on Earth. The climate is changing more and more dramatically than it needs to; a small policy change can have a big environmental and societal impact, while having a small negative (or even positive) overall economic impact. Think about it.

From Jonathan on spiral galaxies vs. elliptical galaxies: “Ethan, you wrote this about elliptical galaxies and spiral ones: “The inner regions of spirals and ellipticals are comparable in densities, but the outer regions are where ellipticals are significantly richer in stars.” Surely this would mean that ellipticals are *more* dense than spirals.”

Now, let’s get away from the never-ending climate debate and let’s take on the Universe! Ellipticals, in general, are larger and more massive than spirals. In the innermost regions, ellipticals and spirals are comparable in density. This means, in the innermost, say, 10-50 kpc, they have similar densities. But if you go out to 100 kpc, 200 kpc, 400 kpc, or more, spiral galaxies typically have some gas and no stars. Ellipticals, though, have significant populations of stars. Not as much as the inner regions, but there are stars present. Overall, the density of an elliptical is lower than that of a spiral, due to its much larger overall volume, and those large regions of lower overall density. But the number of stars and the density at every radial distance is larger for ellipticals than spirals.

I hope that clears things up!

From Outtatheblu on the Universe’s first black dwarf: “I am curious about the dark star’s properties when it finally cools down. Assuming no further accretion, it’s mass and size should be roughly the same order of magnitude as it is currently (im unsure how much mass it would lose through its EM radiation from now until it cools). Once the plasma cools and stops emitting light, would there be a (solid?) mass left over with similar neutron-star level density?”

Don’t underestimate gravitational contraction; it’s plausible that it will have the same mass (to within less than 1%, which comes from energy loss due to E = mc^2) but its radius may be up to around 20%-50% smaller. The mass left over would be held up by degeneracy pressure (thanks to the Pauli exclusion principle), where it’s electron degeneracy for black dwarfs and nucleon degeneracy for neutron stars. But black dwarfs would have roughly white dwarf-level densities, which is only about one-millionth that of neutron stars.

From CFT on the anti-global-warming train: “How can he honestly claim that temperature readings taken from actual measurements from balloon and satellites are ‘bad data’ in comparison to utter ‘non data’ forcasts generated by computer models based on….theory?”

He doesn’t. He claims that uncalibrated or incorrectly calibrated data is ‘bad data’ in comparison to correctly calibrated data.

And he’s right.

There are many ways that being alive today is better than at any point in the past, as the data clearly shows. But that doesn’t mean there aren’t genuine problems facing the world, and that’s definitely no excuse for being dishonest about those problems. Your opinion carries no weight in matters of fact, nor does mine or anyone else’s. But all of our opinions matter in making policy and in our public statements, which influence others around us. If we take counterfactual ‘opinion’ stances then we are misleaders at best and wholesale liars at worst. We must be better than that. Even when the data leads us to places we’d rather not go, we must go there. Anything less is a lie.

From John on the distance from the farthest galaxy to the Universe’s edge: “Thank you. It’s good to be reminded of the different expansion rates at different times since the end of inflation. The influence of time on the universe is easy (at least for me) to underappreciate.”

You have to remember that the expansion of space started out very, very fast, and dropped precipitously over time. Today, it’s down at around 70 km/s/Mpc, and it will level off to a constant of about 50 km/s/Mpc due to dark energy. But in the past, when the Universe was smaller, the matter density was greater by a factor of a^(-3), where a is the Universe’s scale factor (taken to be 1 today by convention). When the Universe was half its size, the matter density was eight times as great, and the expansion rate fell off as a^(3/2). When the Universe was very, very small, radiation dominated, and radiation density was greater by a factor of a^(-4), and the expansion rate fell as a^(2). Here, look at this graph:

There are three different “slopes”: the “radiation” slope (until matter dominates radiation), the “matter” slope (until dark energy dominates), and then an exponential growth rate once dark energy dominates. Note the extrapolation into the future, and how dramatically the Universe grows. It’s those last few logarthimic “moments” that matter most. When the CMB was emitted (at about 10^5.5 years), the Universe was about 10^8 light years (100 million light years) across. That’s a big number, but not that big. Today, the CMB is located about 900 million light years from the edge of the observable Universe; everything continues to expand. Never forget!

From Steve about this graph: ” I take it that on the timeline our galaxy is essentially at the edge of the universe.”

Nope; we are, from our perspective, at the “Universe today” mark, and we measure outwards from our location and backwards from our time. As far as we are concerned, we place ourselves at the “origin,” not the edge.

From anneb on whether galaxy clusters prove dark matter: “Dark matter was invented to explain these lensing effects, but invented matter is not the same as discovered matter. Some theorists claim dark matter doesn’t exist at all and these lensing effects are caused by something else.”

First off, dark matter was not invented to explain these lensing effects; it was invented for a completely unrelated gravitational purpose: the speeds of individual galaxies within clusters. That one “invention” has many, many observational consequences, and the magnitudes of strong and weak lensing are two of them. So are galactic rotation curves, fluctuation patterns in the CMB, the large-scale power spectrum of the Universe, baryon acoustic oscillations, dark matter filaments, and many others. You are correct: some people will only be convinced by a direct detection of a dark matter particle; anything less will be unconvincing. But until you can invent a “something else” that does just as good for the full suite of data, dark matter will remain the leading idea.

From Douglas Watts on the age of the Universe: “The Standard Model doesn’t seem to prohibit a Universe of age 1 Trillion years (72 of ours stacked together). At a quintillion maybe proton decay might have an effect … but so what. Is the 13.8 GY age of the Universe simply stochastic?”

The age of the Universe isn’t randomly determined; it simply “is.” We measure the expansion rate today, the composition of the Universe today, and extrapolate backwards. That’s where the 13.8 billion year figure comes from.

Now, are you asking, “what does the Universe’s age need to be to permit an Earth-like planet around a Sun-like star with enough time for a human being to evolve on it?” If so, the answer seems to be at least 5-7 billion years, and that it could happen trillions of years in the future. But there is some non-infinitesimal, significant, and arguably large probability that the answer of “around now” is a pretty good one. In that sense, the 13.8 billion years we have simply “is.”

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, but smaller than Uranus and Neptune. Hypothetical lightning lights up the night side. Image credit: Caltech / R. Hurt (IPAC).

From Jason on hunting Planet Nine: “From my understanding, telescopes in general can only see what the human eye can see. […] Is it possible that next generation optics will be able to provide a better view of that area of space, and thus provide more context to the evidence (or lack there of) of the existence of Planet Nine?”

Telescopes can see much more than the human eye can see: they can see wider ranges of wavelengths, they can see far fainter objects, and they can see resolutions way beyond what our eyes can. Now, for a distant planet, you have to remember that brightness falls off as 1/r^2, which means the amount of sunlight striking planet nine is very small compared to the amount striking Neptune, and then the reflected light must make the return journey, which also sees the brightness fall as 1/r^2. Pan-STARRS hasn’t seen Planet Nine because the magnitude of Planet Nine is too faint. Better optics won’t help much; we already capture 80%+ of the light that’s out there. But larger-aperture telescopes will help, and wide-field views with long integration times will help. What an 8-meter telescope can do in an hour, a 30-meter telescope can do in about 4 minutes, and with better resolution. It’s not the optics, but the size and field-of-view, that must improve.

Illustration of the density (scalar) and gravitational wave (tensor) fluctuations arising from the end of inflation. Image credit: National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) – Funded BICEP2 Program.

From Frank on the nature of gravity: “Isn’t it possible gravity is not a force but just bending of spacetime?”

No matter what its nature is, gravity is just as surely a force as anything else. What we can observe and measure is more important than what you conclude its “true nature” is. What you are asking is if gravity must be a quantum force at some level. Let me ask you this question: what happens to the gravitational interaction of an electron as it passes through a double slit?

If the answer is to be anything other than “nonsense,” gravity must be a quantum phenomenon, inherently. We currently have no idea how we’d interact with a graviton to detect its nature directly, but detecting gravitational waves from inflation would also prove it, since there is no way to generate them without gravity being a quantum phenomenon. There is hope for this, observationally, after all.

Astronaut David Scott salutes the American flag during the Apollo 15 mission. Image credit: NASA.

From Denier on the 21st vs 20th century: “I’m sure we’ll learn some new stuff in the 21st Century, but ‘best one ever’? Better then Einstein? You really think that?”

The 20th century saw some tremendous scientific achievements, no doubt. You listed a great many of them yourself in your comment. But how many of them are astrophysical achievements, as opposed to aeronautics, aerospace, particle physics, etc.? I think the 21st century will be poor for particle physics and aeronautics, good for aerospace, but great for astrophysics. The Universe is a vast and strange place, and even with all that Hubble has done, we’ve only uncovered a tiny fraction of what’s really out there. For what we know and what we are capable of, unless we fail to fund astrophysics, I have little doubt it will turn out to be an incredible century that will surpass the 20th in a great many ways.

How cosmic inflation gave rise to our observable Universe, which has evolved into stars and galaxies and other complex structure by the present. Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF interagency task force on CMB research. From his book, Beyond The Galaxy.

From Sinisa Lazarek on the joys and perils of inflation: “…if inflation is correct, and some day we get some more solid notions of the conditions that ought to have existed in order for inflation to occur (assuming inflation in itself is not “the default” state), then we might be able to shed some more light on what the things that preceeded it might have been.
But just by reversing the clock so to speak.. we get to inflation and all prior history is erased”

Inflation, by its nature, wipes out anything that came before it. But when we look back at our Universe, the final 10^-33 seconds (or so) of inflation do leave their cosmic imprint on the Universe. There are additional predictions that arise that may yet be confirmed, including: spatial curvature at the ~10^-5 level, a rolling scalar spectral index at the 0.1% level, and primordial gravitational waves at the non-zero level. As our observations of the original light in the Universe, the CMB, continue to improve, we just might find this evidence.

From Cleon Teunissen on probabilities and likelihoods in inflation: “Ijjas, Steinhardt and Loeb have pointed out that as the depth of understanding of inflationary models has increased, more and more problems have arisen. The way I understand it: IS&L have for example pointed out that it is now understood that once inflation starts the overwhelmingly probable course of events is that the inflation continous forever. As I understand it: while it is _possible_ for inflation to end, that is an exceedingly improblable outcome.”

The thing is, we have no way of measuring or calculating what the probability of many things are in inflation. If something has an infinitesimally small probability of occurring, we’re kind of screwed, and Ijjas, Steinhardt and Loeb are correct. But if there’s a finite, non-zero probability, and we have many realizations, we’re fine, and the IS&L argument holds no water. What you are seeing, above, is an example of “eternal inflation,” where it continues for an eternity, but has a ~50% probability of ending at every stage. This doesn’t pose any problems for our Universe, even though the overwhelming majority of phase space (the space of possible outcomes) at any given time consists of inflating spaces rather than non-inflating ones. If an inflationary model that gives our Universe has a non-zero, finite probability of occurring, we, too, are fine.

And finally, from Anonymous Coward on the greatest mystery of the Crab Nebula: “Do other known supernova remnants out there exhibit this same kind of mass discrepancy as the Crab Nebula, or is the problem unique to it?”

To the best of my knowledge, reconstructing the masses of other supernova remnants yields a similar problem. If you attempt to estimate the mass of the Cassiopeia A supernova remnant, you find ~1-2 solar masses of material in there, which doesn’t make sense for a Type IIb supernova. However, there is the possibility that its hydrogen envelope was entirely stripped away, and so there’s the possibility that there’s an outer shell we haven’t yet discovered that contains additional mass. This may be the case for the Crab Nebula too; finding what’s out there in the Universe is a much harder task, given our instrumental limitations, than theorizing about what ought to be there!

Thanks for a great and thoughtful week, everyone, and I’ll see you back here tomorrow and all of next week for more Starts With A Bang!