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Comments of the Week #79: from inflation and dark energy to the Higgs [Starts With A Bang]
“Today we have touched Mars. There is life on Mars, and it is us—extensions of our eyes in all directions, extensions of our mind, extensions of our heart and soul have touched Mars today. That’s the message to look for there: We are on Mars. We are the Martians!” -Ray Bradbury
It was a busy week, from science to politics to the simple question of Earth’s color here at Starts With A Bang. As always, you didn’t disappoint, with plenty to say about it all, and I’m stoked to continue the conversation. Just in case you missed anything:
- Are inflation and dark energy connected? (for Ask Ethan),
- The world’s oldest street artist (for our Weekend Diversion),
- Ceres’ secrets revealed (for Mostly Mute Monday),
- Could black holes be the engines of new galaxies? (a great Astroquizzical by Jillian Scudder),
- The difference a dark sky makes,
- and How the Higgs gives mass to the Universe (for Throwback Thursday).
I also had a couple of life-related (?) pieces in our Solar System over at Forbes:
- Where In Our Solar System Are We Most Likely To Find Life?, and
- How The Discovery Of Water On Mars Might Make Life Possible Today.
Also, for those of you invested in our Patreon, we have podcasts coming for all now, but patrons get it first! In addition, we’re more than 2/3rds of the way towards having an official poster on the scientifically accurate timeline of the Universe created; it’s going to be awesome! That said, let’s dive on into our Comments of the Week!
Image credit: Bock et al. (2006, astro-ph/0604101); modifications by me.
From Ragtag Media on the end of inflation: ““The early Universe’s inflationary period lasted for an indeterminate amount of time — possibly as short as 10^-33 seconds, possibly as long as near-infinite”
How do you go from 10-33 to near Infinite time frame, what am I missing here.
Anyone?”
There were a lot of attempted answers to this, but I meant something very specific, and I wanted the opportunity to clear this up. Inflation does a few very important things in the very, very early Universe:
- it causes a very rapid, exponential expansion,
- it takes the topology of any pre-existing Universe and stretches it flat,
- it takes any pre-existing particles and expands them so far away that there’s at most one left in what becomes our observable Universe,
- it creates quantum fluctuations that get stretched across the Universe, resulting in the seeds of cosmic structure,
- and finally, inflation comes to an end by “rolling down the hill” of the inflationary potential, with the decay/oscillations giving rise to matter, antimatter, radiation, energy, and what we know as the hot Big Bang.
Image credit: Cosmic Inflation by Don Dixon.
The problem is, we exist in the Universe after this hot Big Bang takes place. We can only observe what’s causally connected to us — what’s had time to reach us in the expanding Universe limited by its 13.8 billion year history and the speed of light — and the only “evidence” left to us in the Universe from before the hot Big Bang comes from the final 10^-33 seconds (or so) of inflation.
So from an evidence-based point of view, we only have the last 10^-33 seconds left to us. There are viable theoretical models where inflation lasts only that long and no longer, and there are models where it lasts much longer, and there are even models where inflation is eternal to the past. So we have a hard lower limit on time, but no upper bound. And that’s where it comes from.
Image credit: HEMEDIA / SWNS Group.
From Broadstreet on the world’s oldest street artist: “Why don’t you put a description under the pictures? Let my guess: you are busy writing “Image credit:””
I sure am. Crediting images is vitally important; people need to be attributed for their work. I’m also of the opinion that illustrating my posts is of paramount importance, too, as visualizations help a great many people better understand what’s going on.
Do you really need image captions for pictures of knitted street art? I do my best to provide captions where I feel the image needs an explanation for what’s going on, but to me that’s rather rare. What do all of you think?
Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
From PJ on Ceres’ secrets: “Have been keeping an eye on Dawn/Ceres progress here:
http://dawn.jpl.nasa.gov/ I’ll stick with the salts.
What an achievement so far !”
I agree, and I think that salts is probably the leading explanation right now. I would’ve bet on ice a while ago, but with the angle the Sun is at and the level of radiation Ceres receives, I’m pretty sure it would’ve sublimated in short order. Salts appear the likeliest explanation to me, too, which probably means something pretty amazing:
- there must’ve been ions that dissolved in some liquid (water, anyone?),
- which then evaporated/boiled/sublimated,
- leaving these salty regions behind,
- which were then exposed by impacts.
If that’s true, isn’t that a hell of a story?
Image Credit: ESO/M. Kornmesser.
From Wow on black holes preceding galaxy formation: “A clincher for SMB preceding galaxy formation would be finding that they’re more liable to be offset from the gravitational centre of the galaxy the younger they are.
After all, there’s no reason to suppose that the black hole forms where the most collapsible matter happens to be.
My thoughts have always been that quasars may be two or more SMBs colliding to form what will be the galactic SMB we see in older galaxies like ours, or M31.
Such events may even say something on how you get an elliptical compared to spiral galaxy. Spirals would form as the result of the orbit of two merging black holes being naturally a planar event when there’s only two such objects doing the business.”
This — all of this — is incredibly physically interesting. It’s not thought you can have a supermassive black hole without having a period of star formation and the gravitational collapse and fragmentation associated with star formation, but until we can probe the first stars and proto-galaxies, we won’t know for sure.
Image credit: NASA/JPL-Caltech/R. Hurt (SSC).
But I’m not entirely sure having massive black holes offset from the galactic center early on would be an indicator they precede galaxy formation. It’s easy to imagine a scenario where young black holes form all over, say, a spiral galaxy, and then merge together and migrate towards the center, the same way mass segregation works in all sorts of astrophysical objects. We do see a few instances of galaxies with dual black holes, and some of them are (still) spirals. Here’s one of my favorites.
Image credit: Gemini Obsercatory / AURA / Sydney Girls High School Astronomy Club / T. Rector / A. R. Lopez-Sanchez (AAO) / Australian Gemini Office, composite with Chandra X-ray Observatory, stitching by me.
There’s a merger going on, to be sure, but the “smaller” galaxy (about the size of the Milky Way) very clearly has two black holes in it, as the X-ray shows.
But there’s no reason to believe this galaxy will become an elliptical. I think your scenario, Wow, is plausible, but by no means is it going to explain 100% of what we see.
Image credit: GNI Phoenix International, via DIYTrade.com.
From LdB on the Higgs and mass: “Ethan the article is a bit misleading, it reads like you think the Higg’s (sic) is the universal giver of mass.”
Let me be universally clear, then: the Higgs is the universal giver of mass to particles with a non-zero rest mass, as far as we can tell. This may or may not include dark matter; this may or may not include neutrinos. (Both of these could get their mass from a different mechanism.) But all the quarks, all the charged leptons, the Z and W bosons, and the Higgs boson itself all derive their rest masses from the Higgs field.
Now, composite, bound combinations of these particles have other sources for their mass: protons get their mass from the strong force, for example. But yes, the Higgs gives mass to everything. Most importantly, without a mass — if the quarks were all massless — bound states like protons would not be possible. So while there are other sources for some forms of rest mass, there’s quite possibly nothing at all with a rest mass without the Higgs.
Image credit: Wikipedia / Wikimedia Commons user Qashqaiilove.
From david on couplings: ““The fact that there’s a self-coupling — something special to the Higgs — makes the Higgs boson different than all the other particles, but also explains why it has mass at all.” — Don’t gluons also self-couple?”
Yes! Yes they do. In fact, gluons — since they have a color charge — couple to other (colored) gluons, which is part of what makes QCD so difficult to do perturbative calculations with. If you’re willing to go to higher loop order, photons self-couple as well (even though they don’t without “loops”), which is how you can have photon-photon interactions. The W’s and Z’s likely self-couple too, meaning that all the bosons do.
So I misspoke here.
Image credit: Ned Wright / Sean Carroll, via https://ned.ipac.caltech.edu/level5/March01/Carroll3/Carroll4.html.
And finally, from Pavel on gravitational self-coupling, “And gravitons as well…”
This one is really interesting, and — of course, like all aspects of quantum gravity — is an open area of research. (See here, for an example.) Yes, if you write down a field theory, you do get terms where gravitons do couple to one another and get exchanged in graviton-graviton interactions. But this does not necessarily mean they self-couple, not if these interactions, when all the terms are accounted for, wind up being equivalent to a free field theory. (And they may; this happens for scalar Φ^4 theory, which appears to have non-zero terms at finite loop order.)
So gravitons may self couple, or they may not. It will take a lot more physics — theoretical and experimental — to know for sure! Thanks for a great week, and I hope we all learned a lot together; I know I did!
Source: http://scienceblogs.com/startswithabang/2015/10/03/comments-of-the-week-79-from-inflation-and-dark-energy-to-the-higgs/
