Comments of the Week #63: From the heat death to black hole infall [Starts With A Bang]

“Men who wish to know about the world must learn about it in its particular details.” -Heraclitus

This past week at Starts With A Bang put on quite a show, and you — as always — didn’t disappoint. If you missed anything, here’s what went on:

• Learning to chill (a guest post from Paul Halpern),
• Does a black hole have a shape? (a fascinating Astroquizzical from Jillian Scudder),
• Muons, relativity & a new record? (for Ask Ethan),
• Keep the Universe going (introducing our Patreon, for our Weekend Diversion),
• Sunsets from space (for Mostly Mute Monday),
• Pluto’s unique moons, and
• What would you see as you fell into a black hole? (for a bonus Throwback Thursday).

In addition to these, I had two new pieces over at Forbes:

• New Record Set For Brightest Galaxy In The Universe, and
• The Voyage No One Wants To Take: Why The Hyperloop Is A Catastrophe-Waiting-To-Happen.

You all said so much and I don’t want to waste any time, so it’s onto your Comments of the Week!

Image credit: Courtesy of http://science.dodlive.mil/.

From Denier on the (observable) Universe’s finiteness: “I find the idea of there being a finite amount of thoughts that can occur in the universe to be a serious weight. Some really stupid things can occupy my thoughts. To think I am wasting one of the universes finite thought count on American Ninja Warrior is… awesome. After thinking about it, I’m not conserving anything. Go Jessie Graff!! You guys need to stop wasting the universes’ thoughts on your stupid stuff.”

When you think about it, it couldn’t be any other way. To have a thought as we understand it, you need for at least one electron — a particle within our Universe — to travel from one location to another. Everything we understand as a thought has, at its root, an electrical signal, and that involves information transfer. And yet, you need to have something happen to cause that electron to transfer: you need a difference in energy between the past state and the future state to make it happen.

And that takes something out of your Universe. We have a huge observable Universe at our disposal, with some 10^80 electrons and protons, a billion times as many photons and neutrinos and antineutrinos, who-knows how many particles of dark matter, and a finite amount of dark energy atop it all. And yet, the total amount of energy within it is finite. The total amount of energy that can be released is finite. And so even given an infinite amount of time, the total number of “thoughts” that our Universe will experience is finite as well. So enjoy your Ninja Warrior, Denier, I know I will.

Or, as Wow so eloquently put it:

“It’s only a waste if you wanted to do something else.”

From Alex on black holes: “Are anti-matter black holes possible theoretically? An encounter of a matter black hole with the anti-matter one would probably be the most violent event imaginable.”

This is one of the most important components of something you need to understand in order to both “get” black holes, and also to understand why there is such a thing as an information paradox with black holes. You see, there are only a few things black holes “remember” from before their creation:

• what the total amount of energy (mostly mass) was that went into creating them,
• what their total electric charge is (and, if magnetic charge exists, what that is; possibly color-charge as well),
• and what their angular momentum (i.e., spin) is.

That’s it! It doesn’t care if you were made from neutrons, neutrinos, atoms, baryons, leptons, or even matter or antimatter. All it remembers is what the mass of the things that went into it were.

This should bother you! If you had a neutron star and an anti-neutron star — which you could create simply by having enough anti-hydrogen in one place to make a massive enough star out of antimatter — and collided them, that would be a catastrophic release of energy, on the order of ~10^48 Joules of energy. That’s about 10,000 times the energy of a supernova.

And yet, if you increased the mass of each one just a little bit, and made a black hole (and an “anti-black hole”), they’d just merge together to make a larger black hole. The “anti-black hole” is now indistinguishable from the regular black hole. And that probably doesn’t feel right to you, but that’s the way things are, according to the physics we understand today.

Image credit: Fermilab, via http://www.symmetrymagazine.org/breaking/2009/11/19/what-a-muon-collider-could-look-like.

From Omega Centauri on muon colliders: “As the particles in the beam, as measured in the earth’s frame, still decay the beam itself will be radioactive, giving off high energy electrons (or positrons) along its pathway, there will be inevitable leakage of these electrons. How much of an obstacle is this path radiation expected to be?”

The nice thing about magnets that bend charged particles in a circular shape is that the magnets must be tuned to curve particles of a very specific charge-to-mass ratio in a path of a particular radius at a particular energy/momentum. Your electrons will be moving with only a fraction of the muon’s pre-decay momentum (because the momentum is split also among the neutrino and antineutrino decay products), a greater velocity (because the electron’s mass is over 200 times less than the muon’s), and — most importantly — a significantly different charge-to-mass ratio.

Whenever a muon decays, the electron will quite rapidly slam into the collider wall. So long as it doesn’t do so in the detector zone (and even if it does, it will be easy to separate out due to its small transverse momentum), and so it won’t confound our collider results.

Sometimes, other commenters do the work for me. Michael Kelsey, in this case, beat me to the punch:

“In a muon collider storage ring, the electrons will have the wrong mass (and hence the wrong momentum) to be properly bent by the magnets. Instead, they’ll hit the outward sidewalls, which will consequently need to be shielded and extensively cooled, probably with an “alcove” design (a horizontal extension on the outward bend side).

This situation is quite similar to typical electron storage rings (such as the SLAC B-Factory, where I worked on the BaBar detector), which have to deal with the [synchrotron] radiation from the electrons.”

Image credit: screenshot from our Patreon: https://www.patreon.com/startswithabang.

From RagTag Media on my new Patreon venture: “Aren’t ya suppose to just write books annually and require students to pay exorbitantly inflated prices for them?
Is that model no longer relevant?”

The funny thing is, that model was never really relevant. Which is to say, even if I wrote a god-awful giant textbook, charged $200 a pop for them, and managed to sell, say, a few hundred copies of it a year (not bad!), I’m not making tens of thousands of dollars, as math would indicate. Thanks to the way publishing houses work, I’d make about 7-10% of that, which wouldn’t be worth the effort, to be frank.

As it is, my first book is coming out later this year (I’m proofreading it now!), and I hope that everyone who’s curious about the Universe — from high school students to intro-to-astronomy students to undergrad majors to grad students to simply interested adults — reads it. I know it won’t be enough for me to make a living, but the whole “telling stories” about the thing I love, the science I worked so hard to learn and understand in detail, is what I do now, and would like to make a living doing. Hence the Patreon campaign.

And an amazing thirty of you have pledged to sponsor me so far, in just the first week! Including Denier, who writes:

“You make a good living by providing a product society finds valuable. I do too. And I totally support Ethan in his willingness to venture outside the stupid tenure-textbook model. I hope all of you do because all of you obviously see the value in his work or you wouldn’t waste your time coming here. Even if it is for $1, hit the button.”

I am officially taking money from Big Denial*** and I’m not even ashamed to be doing so. There’s so much to know for all of us, and I’m happy to get to share what I know with an audience that feels that the knowledge I have to share is valuable for its own sake. You all should get to share in it, and whether I should or not, I want to be the one (or one of the ones) who tell that story. Hopefully, we’ll find a way to make that happen. If you have the resources to make any contribution at all, it’s greatly appreciated, even if it’s less than the suggested minimum of $1/mo. You can become my Patron by clicking here.

(*** – Assuming Denier is actually Big.)

From PJ on sunsets from space: “Like the second photo with the moon to the right of the field. Nice curvature on the horizon, too. Flat earthers should take notice.”

One of my favorite things about photos like this is that you can clearly see that not only is the Earth round (and pardon my sarcasm, but duh, we’ve known that for thousands of years), but you can clearly see how the Sun illuminates both the Earth below and also reflects off of the Moon, causing its phases. You can see, based on the geometry, that the Sun must be much farther away from Earth than the Moon is. And that’s what you can learn just from a single picture.

Isn’t science wonderful? I mean, think about it for a moment, all we’ve got here is one picture of the three most prominent objects in our experience: Earth, the Moon and the Sun. We’ve got a snapshot of one moment, taken with a run-of-the-mill camera. And there’s so much we can learn just be applying mathematics to what we observe. That’s how the scientific process works, and this is a classic example of how you could learn all about the Universe just by asking it questions about itself.

From Ed on Pluto’s tumbling moons: “Umm, Saturn’s moon Hyperion also tumbles.
http://earthsky.org/space/sunday-is-cassinis-last-close-sweep-of-saturns-moon-hyperion“

This is true, and profound, and a puzzle. It’s funny how for the Pluto system, it’s not a puzzle, because we fully expect the moons to have their orbits perturbed by the presence of a second large mass. As it tries to move stably around the Pluto-Charon barycenter, the tidal torques induced by the separated masses cause the axial orbit to move chaotically, where “chaos” in this case means that it changes regularly, but in a fashion that is very difficult to accurately predict on anything but the shortest timescales. The physics is deterministic, but we’re not smart enough to determine it.

But then there’s Saturn’s moon Hyperion.

It’s heavily cratered, it’s huge at 100s of kilometers in all directions, it’s pumice-like light, it’s roughly 50% hollow, and its orbit, too, is chaotic. The big difference is we don’t know why. If I had to guess — and this is just a guess — I would bet that its center-of-mass is significantly offset from the center of the object itself, and so “normal” gravitational forces induce a torque that change its axis of rotation over time. But we don’t yet know, even the people who study it for a living.

For the first time, we’ve observed a tumbling moon that we can explain, and that we can use to apply to the orbits of exoplanets around binary stars. That’s what we learn from Pluto’s moons, and that’s a pretty big deal!

Image credit: Cetin Bal.

And finally, from Michael Kelsey on falling into a black hole: “In your article, you write a couple of times that within the event horizon, the singularity (or whatever, see above comments) is “downhill in all directions.”
Back when I took GR in grad school, almost three decades ago, I learned that in the Schwarzchild metric, as you approach the event horizon from the outside, the ‘t’ axis “bends” to point toward the horizon. As you cross it, the ‘t’ axis become[s] “radial,” pointing at the singularity.
Is this just the same statement as yours? Since the singularity is directly in the future (i.e., along the ‘t’ axis), there’s no spatial direction you can move to escape it.”

Both of these viewpoints are 100% consistent with one another; GR has not changed from when you learned it some 30 years ago and when I learned it some 13 years ago. (Hey, we’re like Christa Allen and Jennifer Garner!) The fun thing — and what we have learned that’s new — is that there will be a “least-downward” direction, where the acceleration towards the singularity is minimized, and that corresponds to what you’d experience if you had fallen in from rest. If you fell in with an initial velocity, it will look like one particular direction is “downhill, but not as fast” as all the others, and that corresponds to the “I fell in from rest” geodesic.

So yes, downhill in all directions is the same as saying that all paths terminate in the singularity in a finite amount of time, but it’s interesting that there’s a “downhill-the-slowest” path, which extends “t” for the longest. And that corresponds to the path that puts you falling in from rest. Weird!

Image credit: SXS team; Bohn et al 2015.

Oh! And I almost forgot, a bonus caught-mistake by Robert Nemiroff: “Cool article! Slight nitpick: above it was stated: “… taking over a full half of the sky as you crossed the event horizon”. Actually, the blackness would take up full half of the sky as you crossed the photon sphere, which is 1.5 times further out than the event horizon.”

This is correct, and this is my great blunder. I have made the edit in the article to fix it. The photon sphere is known as “ISCO,” by the way, or innermost stable circular orbit. It’s kind of counterintuitive that if you tried to move in a circle from less than 1.5R, where R is the radius of the event horizon, you’d spiral into the black hole, but those are the breaks. As a result, you’d see only blackness in front of you. Here’s the (annotated) video from Andrew Hamilton that shows this.

Not bad! So thanks for a great week, everyone, and I’ll see you back here, well, tomorrow, I guess, for more wonders and joys of the Universe!

Source: http://scienceblogs.com/startswithabang/2015/06/06/comments-of-the-week-63-from-the-heat-death-to-black-hole-infall/