“Perseverance is not a long race; it is many short races one after the other.” -Walter Elliot

It's been two great weeks here at Starts With A Bang, where we've seen an incredible slew of new articles, new contributions, and literally hundreds of comments where nobody needed to get banned! To all of those who made it out to see me last weekend at NorWesCon, thank you for your incredible support, and to those who didn't, I hope things have gone well for you, and that you've enjoyed all our articles! To take a look back, here's what we've seen over the past two weeks:

We now have over 130 Patreon supporters, and they all have access to this month's podcast (on Time Travel!) a week early; go sign up, even for $1 per month, and get access today! I'd also like to extend a big thank you to everyone who showed up and heard me speak at my local March For Science. And with that big two-week recap out of the way, let's hear and respond to the best of what you had to say on this edition of our comments of the week!

The production of a cosmic ray shower, produced by an incredibly energetic particle from far outside our Solar System. Image credit: Pierre Auger Observatory, via http://apcauger.in2p3.fr/Public/Presentation/ From Michael Mooney on relativity, length contraction and time dilation: "I am (still) saying that appearances might change via relativistic effects but that physical bodies and distances are not affected by different frames of reference."

What if I could prove to you that physical distances are affected by different frames of reference, with a genuine physical experiment? Hold out your hand and hold it so your palm faces the sky, and ask yourself how many muons are passing through it? If you wait about one second, the answer is "one." You can verify this by building a small cloud chamber for yourself. The thing is, this doesn't make sense if distances are not affected by different frames of reference.

A muon lives, on average, for 2.2 microseconds. It travels close to the speed of light, and is created, typically, about 100 km up in the atmosphere. If you multiply 2.2 microseconds by the speed of light, the mean distance a muon will travel is 660 meters, meaning that -- if we do the math -- then all of the muons created in the upper atmosphere should decay away before they reach your hand. But they don't! From our reference frame, the muon's time dilates, and that's why it survives.

But from the muon's equally valid reference frame, the distances in front of it must contract. The atmosphere must be compressed to less than 660 km thick, and the Earth must be contracted itself so that its "towards-the-muon" diameter is less than 1% its transverse diameter. This contraction is real to the muon, and is equally valid to our own perception. If you want the physics in both reference frames to agree, this is what you need to happen. I hope this helps, but I fear that you are so hellbent on your predisposed opinion being correct that no fact will serve to educate you.

A map of world population density from 2012. As the mean per capita income increases and economic prosperity grows, the population growth rate increases temporarily, but then levels off to a constant population. From Denier on some bad assumptions: "How many people will there be in the year 2300? We are talking about Anthropogenic Global Warming so the number of anthropoids is an important detail, don’t you think? I’d be stunned if Ethan put any thought into it before making the prediction. I’d bet he just extended a trend line or parroted a source who did."

There is a move in the wrestling world where the heel hits the face over the head with a folding chair, unnoticed by the referee. When the face picks up the folding chair and goes after the heel, the referee notices, and the crowd howls at the injustice. Just because there are those making exaggerated statements, unthinkingly or maliciously or misleadingly or otherwise, doesn't mean that just because I reached a conclusion you don't like, I exaggerated.

So prepare to be stunned. The number of humans, as predicted by scientists who study population growth, will peak at around 9 or 10 billion worldwide, which will happen likely sometime about 40 years from now. It is anticipated to hold relatively steady or decrease slightly. Meanwhile, the model I used -- wildly unrealistic in its conservativism -- was for global (not per capita, but global) emissions to remain constant at present (2016/7) levels. Don't be so quick to bet against Ethan.

A singularity is where conventional physics breaks down, whether you're talking about the very beginning of the Universe and the birth of space and time or the very central point of a black hole. Distances smaller than the Planck length can effectively be treated as singularities. Image credit: © 2007-2016, Max Planck Institute for Gravitational Physics, Potsdam. From zeuxis on the Planck length: "Determining the Planck length is a pirate’s favorite physics problem."

We needed something lighter. Why did the pirate have a ship's wheel attached to the crotch of his pants?

"Yar, it's drivin' me nuts!"

Fluctuations would need to be many orders of mangitude larger on a very small, specific scale to create primordial black holes. Image credit: NASA / WMAP science team. From Anonymous Coward on primordial black holes: "There are also primordial black holes, which were supposed to be formed by the collapse of slightly overdense regions of spacetime a fraction of a second into the Big Bang."

There are fans of PBHs out there, and they were a good and interesting cosmological idea (and dark matter candidate) when they were first proposed. If a region of space, in the early Universe, is about 68% denser (or more) than the mean density in the Universe, then rather than grow into stars and galaxies, or give up their matter to denser regions, they'll just collapse into a black hole. Unfortunately:

the power spectrum of the Universe has been measured, and the fluctuations are pretty much scale-invariant and are at the 0.003% level, not the ~68% level.

And we have performed exhaustive searches for primordial black holes, and can pretty much rule them out over every possible mass range, with only a slight window still disputed from neutron stars in globular clusters.

Constraints on primordial black holes over various mass ranges. Image credit: M. Cirelli (2016).

Of course it's important to constrain all of this as tightly as possible observationally, but the constraints are so good and so many things would have to be wrong (like inflation, like the idea of a scale-invariant spectrum, like our understanding of small-scale structure) for primordial black holes to exist at all in this Universe. There's no good reason to believe they exist, and lots of evidence against them. Once that last window closes at around 10^20 kilograms (about the mass of a large dwarf planet), you can officially bury the already-nailed-shut coffin.

The Great Observatories Origins Deep Studies North field (GOODS-N), cropped to show the Universe's most distant galaxy, in red. All four of these circumstances needed to come together at once to make this galaxy's discovery possible. Image credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), P. Oesch (University of California, Santa Cruz; Yale University), R. Bouwens and I. Labbé (Leiden University), and the Science Team. From Jonathan on lensing and the most distant galaxy: "If it had to be lensed by a foreground galaxy so we could see it, why doesn’t it appear as a ring? (And why don’t we see the foreground galaxy in the images?)"

Maybe this one isn't lensed, but I thought it likely was. Do you see, in the above image, the "red dot" (this galaxy) and the yellow smudge (a foreground galaxy) just to the left of it? That is a configuration I'm familiar with of where a galaxy will appear to be magnified but not very much distorted by a strong lensing effect. You see this a lot in high-redshift astrophysics, so I just assumed, seeing this familiar configuration visually, that there was lensing at play here.

But maybe there isn't! They talk about this as being an extremely intrinsically bright galaxy, and it may be all due to intrinsic brightness. I had thought there was a mix of the two effects and they were unable to disentangle them, but none of this is discussed in the literature so perhaps I am wrong. It certainly isn't incredibly lensed like the previous record-holder and is much more intrinsically bright, but I believe we will need something like JWST and possibly a better map of the mass in this field before we know more. But I'm very open to being 100% wrong on the issue.

Mongo McMichael vs. Jeff Jarrett, 1997, WCW. From CFT on exemplifying the heel/face/folding chair analogy: "The truth is almost always more complicated than Ethan portrays it, he will go to great lengths to simplify a situation to the point of being factually dishonest by omission of all the pesky details he knows will cause people to more closely scrutinize his assertions and question his undisclosed motives."

And maybe no one will notice, since there is no referee on the internet, and you used a metal briefcase instead of a folding chair...

Measuring back in time and distance (to the left of "today") can inform how the Universe will evolve and accelerate/decelerate far into the future. We can learn that acceleration turned on about 7.8 billion years ago. Image credit: Saul Perlmutter / UC Berkeley. From ketchup on whether dark energy is an illusion or not: "I found it very strange that the people who wrote this new paper would either ignore or be totally unaware of previously published work that disproved their idea."

It's not so much they they're unaware of previously published work that disfavors their idea, but that they start from the assumption -- like many physicists do when they're working on disfavored ideas -- that one particular physical phenomenon is responsible for one particular set of observations despite the known shortcomings. People still discuss the steady-state phenomenon in peer-reviewed publications and simply state that they ignore the known problems with the CMB and with Helium production. People still discuss alternatives to dark matter and ignore the large-scale phenomena they cannot explain without dark matter. And people discuss the "dark energy is an illusion" idea in the same way.

It's not a bad thing! It's not a bad thing at all to continue to explore ideas that don't match the Universe we have. They may, someday, lead to a better understanding of the Universe we actually do have. What is bad is to present this to the public as a viable possibility in its current state. That is what this team did, and that is why it warranted writing such a scathing piece on the matter.

The plasma in the center of this fusion reactor is so hot it doesn't emit light; it's only the cooler plasma located at the walls that can be seen. Hints of magnetic interplay between the hot and cold plasmas can be seen. Image credit: National Fusion Research Institute, Korea. From John on the waste products from nuclear fusion: "That said, I’m less sanguine about the purported pollution free nature of controlled fusion power.

Both Deuterium/Tritium and Deuterium/Deuterium fuels (the fuels most easily “ignited”) produce quantities of neutrons sufficient to contaminate the reactor materials via neutron activation."

This is absolutely true! The nice thing about fusion, though, is that the overwhelming majority of neutrons produced will be absorbed by nuclei that will either be stable (like oxygen-17) or will have a short, manageable half-life (like tritium). Tritium is outstanding because it can often be re-used as new fuel, and also has a short half-life of ~12 years, meaning that it doesn't take all that long (just a couple of centuries) before it can safely be released back into the environment. There is radioactivity produced, but it isn't the long-lived waste that we're having such a problem with in fission reactors.

But I am hopeful that as we learn more about the practical realities of all the different energy sources, we can... what's the expression... Make Earth Cool Again! (As seen at Marches for Science around the world.)

Looking back a variety of distances corresponds to a variety of times since the Big Bang. Entropy has increased always. Image credit: NASA, ESA, and A. Feild (STScI). From Denier on the possibility of time not existing before the Big Bang: "Did the Big Bang mark the point where we transitioned from a 3 to a 3+1 universe?"

We really don't think so. Don't confuse a time-translation-invariant state (like cosmic inflation) with a state where time doesn't exist! We need time, in the moments before the hot Big Bang, to perform a whole slew of tasks, including:

to stretch quantum fluctuations across the Universe, creating the seeds for structure formation,

to stretch quantum fluctuations across the Universe, creating the seeds for structure formation, to stretch the Universe flat,

to create a Universe that has the same temperature and mean energy density everywhere,

to eliminate any high-energy relics (like magnetic monopoles) from the observable Universe,

and so on. If you don't have time -- or if you have a time dimension suddenly emerge -- then all of these things become "initial conditions" problems. And you also have the "we are changing the laws of physics" problem. Why? From what? And how? I'm not saying this is absolutely forbidden, but I don't see how it would work. Pre-big-bang, we have a state that looks the same at any initial time and any arbitrary other time before that (that's what time translation is), but that doesn't mean time doesn't exist!

In classical general relativity, singularities are hard to avoid. But in quantum theories of gravity, such as those with extra dimensions, bouncing scenarios are possible. Image credit: Wikimedia Commons user Rogilbert.

From eric on the size of extra dimensions: "There are either only three, or more with the others being very small and not impacting the fundamental forces. It’s a ‘what-if’ analysis. Those are often very useful in science, as a way of weeding out ideas before we spend money on them. Hypothesize X. Calculate what it mathematically entails. Ask/observe whether reality is consistent with that. If not, reject X…before you waste any significant time and effort trying to test it directly."

This hits a very important point about spatial dimensions: we can constrain the number of them we have based on force laws and how they can be probed down to a particular length scale. For the strong, weak and electromagnetic forces, we can probe distances down to about 10^-18 meters or so: about 1/1000th the width of a proton. We see that there are three spatial dimensions down to that scale. But for gravity, we've only gotten it down to about 10^-5 meters, because we can't probe down to smaller distances yet.

So if we talk about "large extra dimensions," we are talking about "large" as in between 10^-18 and 10^-5 meters, but only for gravity. For all other extra dimension scenarios, where all the forces are allowed to access those dimensions, you need to go to higher energy scales (and smaller distances) than we've ever gone.

A system set up in the initial conditions on the left and let to evolve will become the system on the right spontaneously, gaining entropy in the process. Image credit: Wikimedia Commons users Htkym and Dhollm. From Johnny on black hole entropy: "why do black holes contain so much entropy? Once a black hole forms we lose all the quintillion particles that could have different arrangements and have a single entity with no structure."

So one of the things I attempted to do with the piece I wrote was to define entropy, because the common one used by laypeople -- "a measure of disorder" -- is a pretty garbage-esque definition. If you missed it:

What entropy actually measures is the number of possible arrangements of the state of your system.

If you had two different particles inside (a proton and an electron), there's only one arrangement, since particles are distinct. But if you have two identical ones (two protons), there are two arrangements. How many arrangements are there if you know the total mass, total electric charge and total angular momentum of your system, and nothing else? The answer is a lot, and that's why a black hole has so much entropy.

The Atmospheric Infrared Sounder (AIRS) instrument aboard NASA’s Aqua satellite senses temperature using infrared wavelengths. This image shows temperature of the Earth’s surface or clouds covering it for the month of April 2003. The scale ranges from -81 degrees Celsius (-114° Fahrenheit) in black/blue to 47° C (116° F) in red. Higher latitudes are increasingly obscured by clouds, though some features like the Great Lakes are apparent. Northernmost Europe and Eurasia are completely obscured by clouds, while Antarctica stands out cold and clear at the bottom of the image. Image credit: NASA AIRS. From CFT on privacy: "Is there any particular reason why you failed to mention WHERE you were going to march around?"

Because there are over 600 satellite marches that have taken place on all seven continents, and I don't really like publicly announcing my location all the time. Because I value a little bit of privacy, and I think it's reasonable that I get to choose how much I do or do not broadcast. I respect that for you, don't I, pseudonymously operating commenter CFT whose name, IP address, physical address and birthday I all know but do not share with anyone, right? There are no doubt some people here who know where I am and where I'll be, but that's the reason. Even people who write on the internet can hope for some privacy.

And while many of the people who were marching were political, and many of the messages were political, the march itself was not, at least at the one I went to and spoke at.

Image credit: Sandra W. Roush, Trudy V. Murphy, and the Vaccine-Preventable Disease Table Working Group / Journal of the American Medical Association. From Anonymous Coward on science and politics: "...what is so wrong with using science for political ends? Just so we are on the same page here, by “science” I mean the enterprise of building and organising knowledge in the form of testable explanations and predictions about reality. Why wouldn’t you want to use science so defined to inform politics? It is the best tool we have today for understanding how the universe works, and it was through science that the human species has advanced to the point that it has today. From the Carl Sagan quote that Ethan used to start the article, we’ve arranged a global civilization in which most crucial elements profoundly depend on science and technology. So why the hell wouldn’t you use science to inform politics?"

This was the number one sentiment I encountered at the March for Science. The overwhelming opinion I encountered as to "why you wouldn't" want to do that is because the conclusions that science draws and the realistic, practical (i.e., regulatory) solutions that would emerge run counter to the political or economic or social agendas of others. It's my own opinion that if that's the case, you should still embrace science, and just own the fact that you value something else more highly than the consequences of your actions.

Maybe "economic freedom" of water providers is more important than clean, safe drinking water to you? Maybe the rights of corporations to mine, refine, ship, sell and burn fossil fuels are more important than returning Earth to a mid-18th-century climate? And maybe your personal right to spread preventable diseases to newborn babies is more important than the personal freedom consequences of mandatory vaccination policies?

I can't answer those questions for you; those are questions that should rightly be decided by political institutions. But no one should doubt or deny the science behind those issues. That should be the starting point that everyone agrees on. It's a sad state of affairs -- and why so many of us marches -- that it isn't.

Fred Hoyle presenting a radio series, The Nature of the Universe, in 1950. Image credit: BBC. From John on Fred Hoyle: "It’s a delightful contrast that Fred Hoyle, now known more as a champion of the failed Steady State theory, was one of the principles in developing the successful stellar nucleosynthesis theory."

Hoyle's life was a tremendous mix of triumph and tragedy. On the one hand, his stellar nucleosynthesis advances were incredible, and it's pretty unjust that he wasn't co-awarded the Nobel Prize with Fowler for the discovery of the carbon-12 excited state that makes helium fusion possible. (It is still known as the Hoyle state, and the triple-alpha process by which it's created was also discovered by Hoyle.)

But Hoyle also never accepted the cosmic microwave background as the leftover glow from the Big Bang. He never accepted the COBE results or how the blackbody spectrum ruled out alternative explanations. Since he conflated Big Bang cosmology with creationism, he rejected Earth as a location where life could have originated and instead claimed that life must have originated elsewhere and come to Earth via panspermia.

A mix of scientific brilliance and dogmatic rejection of evidence shaped his life, and today, over a decade after his death, they shape his legacy, serving as simultaneously an inspirational and cautionary tale.

The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. Image credit: APS/Alan Stonebraker. From Klaus Hansen on the spin of a proton: "Good the computers understand it. I would feel better if I also did. There must be a simple reason for precisely 1/2, independently of whether the gluons carry 60 or 59.5% of the spin."

We think there may be, but we aren't sure what that reason is or if there even is such a reason. We like to think there's a good reason why CP-violation isn't seen at all in the strong interaction, but we don't know if there is one. We think that pions should decay to four photons, but we've never seen it. We thought that the electron and proton should have equal-and-opposite magnetic moments, but the proton's is almost three times as large, and the neutron's is almost twice as large, with no obvious-and-simple relationship between them.

I like to say that this simply means there's more science to be done!

The known particles and antiparticles of the Standard Model all have been discovered. All told, they make explicit predictions. Any violation of those predictions would be a sign of new physics, which we're desperately seeking. Image credit: E. Siegel. From Kasim Muflafi on science: "Science is based on definitions and agreed upon postulates."

Oh my no! No, not at all. Science is based on the physical Universe and the rules that govern it. Definitions and postulates are how you get philosophy and mathematics, which can be used as scientific tools, but no, that is not at all what science is.

The standard model calculated predictions (the four colored points) and the LHCb results (black, with error bars) for the electron/positron to muon/antimuon ratios at two different energies. Image credit: LHCb Collaboration / Tommaso Dorigo. From Chelle H.C. on particles: "Today a planetoide discovered in 1988 got to be named after a local weatherman. Looks like the LHC is starting to fall in the same category of relatively unimportant ‘discoveries’."

What you are referring to, at the LHC, is composite particles like mesons and baryons, that themselves are made up of quarks and/or antiquarks in different quantum and energy states. These have been known to exist for nearly a century, and there are literally thousands of them predicted. Finding and measuring them and their behavior is an important part of uncovering information about some of the many unsolved problems in theoretical physics, like the origin of the matter/antimatter asymmetry.

You might look at that and say, "give me a new fundamental particle or I don't care," and that's fine, but others care even if you don't.

The Earth, moving in its orbit around the Sun and spinning on its axis, should provide an extra motion if there's any medium that light travels through. Image credit: Larry McNish, RASC Calgary. And finally, from Carl on how to do the internet right: "Ethan deserves to be treated respectfully. He provides enlightening and thought-provoking articles every day. He presents the mainstream view of science, tailoring his writings to be understood by reasonably intelligent readers from widely-varying backgrounds. Though well educated himself, he frequently checks with experts to make sure he’s presenting information on complex and subtle topics “just right.”

In short, he works hard at his job and we benefit."

Thank you, Carl. I like to think that I'm performing a public good by writing what I'm doing, that I've worked hard to be good at it and that is worth something, and that there's a "silent majority" out there who are actually pleased with what I do. I like to think that people of different political persuasions than my own like and respect what I do (sometimes with certain pet topics exempted), and that most of the people who disrespect me do so for reasons that have nothing to do with me.

But I very much appreciate your call for giving respect to everyone, even to me. We'll see what the response is. Have a great rest-of-your-weekend, everyone, and looking forward to another great week ahead here on Starts With A Bang!