“Einstein, my upset stomach hates your theory — it almost hates you yourself! How am I to’ provide for my students? What am I to answer to the philosophers?!!” -Paul Ehrenfest
It’s been another great week here at Starts With A Bang, and we’ve shed light on a number of wonders of the Universe, from galaxies to dark matter to some of the amazing properties of relativity itself. As always you’ve had plenty to say about it as well. Over the past week, in case you missed anything, we covered:
- How do I write a science blog? (for Ask Ethan),
- The Best (Worst) Fake Astro Pics (for our Weekend Diversion),
- The Galaxy at the Head-of-the-Chain, M84 (for Messier Monday),
- The Temperature of Dark Matter,
- The Night Comes Alive, and
- The 95th Anniversary of Relativity’s Confirmation (for Throwback Thursday).
With a wide range of things to address, what did you say? Without further ado, here are your Comments of the Week!
From Pete A on the topic of writing a science blog: “1) Never assume that one’s readers all reside in the USA.
2) Always use the International System of Units and related nomenclature.
3) Either moderate reader comments or just disable the commenting facility. Genuinely interested readers are quickly turned away from a blog after trying to wade through endless comments along the lines: “Great article!” or “You don’t know what your [sic] talking about.””
When you give advice or an explanation on any subject on the internet ever, you’re always going to find additional gems that either you chose to exclude or that didn’t occur to you in the first place. (Some more excellent ones can be found from Sabine Hossenfelder, FYI.) The first one is particularly important: I remember the first time I tracked my analytics and discovered that a full 50% of my audience (and this has remained consistent) was from outside the USA, including large traffic presences from Europe, Australia, India and Brazil. It’s funny that it didn’t occur to me to give advice about that to Alexander because he’s neither American nor living in the USA.
But as far as comments go, you have to choose what you do about them. Do you allow everything? Nothing? Do you moderate, and have a set of what’s acceptable/unacceptable to you? What I’d really recommend — unless you choose the “nothing” option — is to set up a comments policy for your blog and stick to it. I’ve done my absolute best to set up one that allows almost anything that isn’t terrible, but there’s no way to account for people who have no respect for those with actual, factual expertise in an area. Some people are simply going to confidently speak from a position of ignorance because that’s what they do.
Welcome to the jungle.
From G on the subject of Fake Astro Pics: “Some of those qualify as artistic and evocative. Software has enabled talented people to produce images that could not have been produced before, but, to quote Frank Zappa re. music synthesis software, it’s also “enabled a whole new generation of dreckmeisters.”
So it is that we see (and hear) plenty of good art, plenty more mediocre art, and a large serving of dreck.”
And the big problem with this, as G goes on to illuminate, is that plenty of people know little enough about what’s actually out there in space that they see some of the dreck (or artwork in general) getting passed off or marketed as genuine, when in fact that’s simply not the case. As I showed you, the image above has been circulated, claiming to be the galaxy over the pyramids. In fact, these are two real unrelated images disingenuously merged together and passed off as real.
But there is a place for astronomical art: when it’s used to illustrate important physical systems that we cannot obtain actual images of. For example, exoplanet system, the interiors of star-forming regions, protoplanetary disks, or regions from the young Universe beyond the reach of our telescopes. Thankfully, we have watchdogs out there like @FakeAstropix and @PicPedant to help you separate what’s a real image from what’s not, and hopefully last weekend’s tips will help you from being fooled yourself.
A fun little poem from PJ on our Messier Monday post:
“Aaah, to get cracking,
with the photos and stacking
when the weather is clear once again.
To set up the ‘scope
after SHE says ‘no hope’
I’ll get there after she’s gone to bed.”
Just like regular photography, I’ve still never quite gotten into astrophotography as a hobby for myself. But looking through your own optics at the Universe in the raw? Still unlike anything else here on Earth!
From bobh on the Temperature of Dark Matter: “So the more detailed write up was informative, thank you. I’m missing something on the Lyman-Alpha data though. Clearly since DM does not affect the Lyman-alpha directly because of no electromagnetic interactions between dark and regular matter so any impact would be due to the gravitational interaction between DM [and] norma[l] matter. You say “if the dark matter were warmer, the depths of those lines would be suppressed by a specific amount, while if the dark matter was colder than a certain amount, those absorption lines would be up to 100% efficient”. Wouldn’t it also be true that the absorption lines would be 100% efficient if there were no dark matter at all?“
So what’s happening with these absorption lines? We have dense clouds of gas that have collapsed by a certain amount on small scales in the Universe. They appear at all redshifts, and they increase in density over time.
The big question about dark matter, however, is what does it do to these little structures, and in particular, what does it do to them early on? In hot dark matter models, they suppress the growth of structure early on, meaning that small scales and at high redshift, we’d see absorption lines that weren’t as strong as they were at later times.
We don’t see any evidence of that at all, out to redshifts of more than six. This tells us that if dark matter were ever in thermal equilibrium with the early Universe, it has to have a rest mass of at least tens of keVs, or at least a factor of about 100,000 heavier than neutrinos are known to be. Yes, it’s true that if there were no dark matter — because protons have masses of around 938 MeV — the Lyman-alpha forest would look like this as well… but large-scale structure would be ruined.
Cosmology, you must remember, is like a giant puzzle that we’re trying to put together. You have to look at all of the pieces together to know what you’re seeing.
Again from PJ on The Night Comes Alive: “This shows why some of us put up with frostbite & other nasties just to try to get a decent photo of natures treasures.”
It’s a really amazing video and I was delighted to get to share the science behind it with you. Thanks for sharing your perspectives and your firsthand knowledge of the joys and drawbacks of experiencing it for yourself. And finally…
From Cleon Teunissen on the 95th Anniversary of Relativity’s Confirmation: “My best guess is that only by the 1930′s, with a mature theory of quantum physics developed, it became somewhat meaningful to imagine what would happen to photons in a newtonian gravitational field. As you describe, in such a thought experiment one arrives at a deflection that is about half the value that is predicted by GR.
Surely, in 1919 that thought experiment was too far-fetched to be considered.
But you suggest that in 1919 a case could be made that “Newton’s gravity would bend light”.”
You know, this is sometimes a hot point of contention among science historians, but it shouldn’t be. While wave/particle duality for electrons and particles in general was not at all developed by 1919, it was very well developed for photons! After all, the work of Huygens, Young, Fresnel and Arago was instrumental in establishing that photons definitively exhibited wave-like behavior, and it was Einstein himself in 1905 who taught the world about the photoelectric effect, with photons absolutely demonstrating properties exclusive to corpuscles, or particles.
But all of that is moot: even before E=mc^2 came along, it was theorized that — under Newton’s corpuscular framework — one could treat light as a fast-moving particle. Historically, the Newtonian prediction had been worked out as early as 1801:
The first calculation of the deflection of light by mass was published by the German astronomer Johann Georg von Soldner in 1801. Soldner showed that rays from a distant star skimming the Sun’s surface would be deflected through an angle of about 0.9 seconds of arc, or one quarter of a thousandth of a degree. This angle corresponds to the apparent diameter of a compact disc (CD) viewed from a distance of about 30 kilometers (nearly 20 miles). Soldner’s calculations were based on Newton’s laws of motion and gravitation, and the assumption that light behaves like very fast moving particles.
So there it is: the case could not only have been made in 1919, but it was actually made over 100 years earlier. Let this be the end of that debate for ever and ever.
Thanks for your great comments this week; keep leaving them and let’s keep the great discussions going!