Comments of the Week #132: from dark comets to alien searches

"Ships that could circumnavigate the galaxy in a few years, and count every cell in your body from light-years off, but he wasn't able to go back one miserable day and alter one tiny, stupid, idiotic, shameful decision..." -Iain Banks

And while we can't travel back in time at all to change the actions or events of the past, our incomplete knowledge of the past can always be improved as we move forward. This month's Starts With A Bang podcast is one of the most fun of all, as we cover how we went from mere lower limit estimates of how many galaxies are in the Universe to the first true, accurate number: two trillion!

It was also a fun-and-science-filled week here at Starts With A Bang! Here's a recap of all we've covered:

• Are 'dark comets' the Universe's biggest threat to Earth? (for Ask Ethan),
• Solving the mystery of nebulae in astronomy (for Mostly Mute Monday),
• Why do Supermoons always come in a row?,
• No number of additional galaxies can prevent the Universe from needing dark matter,
• Could our Universe have arisen from a black hole?, and
• Are we looking for aliens in all the wrong ways?

In addition, I just completed a nifty little one hour talk to the University of Michigan amateur astronomy club: the Lowbrow Astronomers, on the topic of the Solar System beyond Neptune!

With all the excitement of the past week, and before we dive into all the wonderful stories we've got set for this coming one, let's give due to your comments of the week!

Image credit: Peter Essick, via National Geographic.

From Sherry on alien abductions: "On August 28 2008 the stars flew one to another leaving a blank sky. Then the space ships came 1st 3 then more. I was abducted. We are not alone. I challenge you to bring to me an ibject. I can light it 4 you and it will tell you its story. I have been running frim man since 2008."

You know, I feel like there's been a tremendous downtick in the number of claimed alien abductions in recent years, as perhaps conspiracy-minded individuals have found other conspiracies to fill their imaginations with. I don't talk about it a lot, but about 10 years ago, I was in the New Mexico desert near Los Alamos national lab, riding as a passenger in a car when I saw a blue disk appear overhead. It moved slowly through the partly-cloudy sky, at an angle, then sped up, faster and faster, and finally disappeared. What I saw was a UFO, in the sense that I had no idea what it was, but I'd be very doubtful that it was aliens.

What's interesting to me is the date that Sherry chose for the abduction was a tumultuous day in the United States for many people of certain... political persuasions. It was the day that Barack Obama officially became the first black nominee of a major party in America. I'm not saying I don't believe you, Sherry, but I think there are a lot of questions that many people would have for you. But if you were truly abducted, perhaps you have a bunch of questions, too!

From Omega Centauri on hurricane speed: "Max cyclone energy. There is something like that in meteorology, hurricanes are heat engines taking the heat in the underlying ocean and dissipating it at the cloud tops. The maximum storm strength is limited by this ocean heat (and the finite coldness of the atmosphere several KM up. So a very long track won’t allow a storm to surpass this value. Now the horizontal extent of a storm usually increases with time, so what one would expect from having a larger ocean, is similar max wind speeds (and lowest pressure), but possibly larger storms."

I think that's perhaps a nice additional point to make about hurricanes hundreds of millions of years ago: with larger, warmer oceans and -- quite possibly -- larger continental shelfs, there are some additional effects.

1. These storms should be much larger in extent, promising significantly more damaging weather events for the coastal regions that get struck.
2. These storms may often strengthen significantly just before landfall, as the warm ocean water just off the continental shelf (as mentioned by Wow) could cause a larger temperature gradient.
3. And that a potentially greater vertical extent for a hurricane could result in a more energetic hurricane with larger wind speeds.

In any case, as we make the planet warmer, we're making these storms worse. But only by a little bit, and we're a long way from reaching how devastating they were hundreds of millions of years ago. Of course, today they cause a lot more property damage, since there's a lot more developed property... at least, so we think.

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, under a c.c.-by-2.5 license.

From Carl Bargainer, on catching my entropy-laden mistakes: "Ethan says: “The “cooled” Universe is at lower entropy than the hot Universe, but that’s also because it’s more expanded and clumpier, not just because it is cooler.”"

I did say that. I should have said higher, not lower. My mistake. An expanded, clumpier, cooler Universe has less ability to do work, and is in a higher entropy state. Thanks for not letting me get away with a slip-up!

Comet Lovejoy, as seen from the International Space Station, poses no threat to Earth. Image credit: NASA / ISS.

From Omega Centauri on dark comets and the alien invasion: "We could imagine a manufactured object with very low observables, as observed only from a single easily predicable point, like the earth.
A mirror whose reflection of the sun missed us would be very difficult to see. But, that’s obviously not a natural object, if super powerful aliens wanted to surprise us like that, there’s not much we could do."

So you liked the part of my story where I said, "What if an incoming, highly reflective comet were oriented bizarrely? What if it was quite icy, but reflected all the sunlight that struck it away from Earth, like some kind of strange crystal?" Only then you want to have it be made out of an actual crystal, rather than ices, so that it won't begin evaporating or producing a tail as it gets close to Earth. A manufactured, alien weapon designed to destroy us.

A stealth comet.

You monster.

I think you just stumbled upon a topic for a new sci-fi apocalypse story.

From PJ on the latest Mostly Mute Monday: "Thanks, Ethan; as usual, a great set of photos..."

I'm super-glad you enjoyed them! But also, that's a bit of a reminder to me that I'd like my Monday posts, as short and visually stunning as they are, to also contain a fair bit of science in them.

Challenge accepted for tomorrow!

From eric on Supermoons: "It did look quite impressive the other morning on my drive to work. But I figured that was just due to air clarity and the half-lighting of the dawn. Now that I know the effect is real, I’m looking forward to November."

The November Supermoon will be the closest, fullest, brightest perigee Moon since 1982, and until the 2030s. Although I can't do it myself, people who watch full Moon after full Moon can tell the difference easily between apogee and perigee full Moons simply by inspection. But if you have continuously clear skies, check for the large-small-large pattern in the angular size of your full Moon -- that coincide with a small-large-small pattern in the size of your crescent Moons -- with a period of 411 days. I'm curious to know how many of you will notice an effect, vs. how many of you won't. (And that's assuming we're not fooling ourselves!)

A guy eating a big slice of big pizza at Big Lou's. Image credit: Sam DeLong of flickr.

From Naked Bunny with a Whip on pizza sizes: "Don’t knock that extra 7% of pizza, Neil."

You know, Neil and I both went to the same High School in New York, although we were about 20 years apart. For him to say,

“The supermoon is a 16-inch pizza compared with a 15-inch pizza. It’s a slightly bigger moon; I ain’t using the adjective ‘supermoon'”

is a little bit puzzling to me. Pizza is an important part of a high schooler's life in New York, perhaps more than anywhere else. I had the local pizzeria by where I grew up (shoutout to Nick of John's Pizza), but I also had the pizza place by my school where friends of mine and I would often hang out, like teenagers do. And there was nothing worse -- on a high schooler's budget -- to get the tiny slice for your $1.50.

The problem is that, if you're talking diameter, even though 16" is only 6.7% larger than 15", a 16" pizza is actually 14% larger in terms of edible pizza than a 15" pizza, and is 31% larger than a 14" pizza. If you consider that most pizzas have a 1" crust on them, a 16" pizza has even more of the good stuff -- the part of the pizza with the toppings and cheese -- compared to the smaller sizes: 16% more than the 15" and 36% more than the 14".

In other words, you might not care much for a Supermoon versus a Micromoon, but don't you dare try and sell me a smaller pizza and pass it off as the large size!

The bigger a black hole's mass, the larger the area of its event horizon is. The quasar illustrated here has a black hole of 2 billion Solar Masses. Could a 4D black hole of ~10^25 solar masses or more been the source of our Universe? Image credit: ESO/M. Kornmesser.

From Omega Centauri (you're cleaning up this week!) on black holes spawning other Universes: "So if this theory holds water: An N dimensional universe which creates blackholes, creates N-1 dimensional universes.
So perhaps the 4D universe was in turn created by a 5-D universe/BH?"

Black holes are nature's way of reducing your dimensions quite easily. But I want you to think, for a moment, of how God-like a higher-dimensional creature would appear to us. They would be able to scramble our internal organs without ever breaking our skin, or perform open heart surgery without opening our hearts. They could make objects appear, disappear or teleport at will. They could add or take away components of our existence willy-nilly, with no apparent cause at all. And they could do it because of the extra orthogonal degree of freedom: because of the extra dimension.

It would be as easy for them as it would be for us, a 3D creature, to draw, erase, or transport materials from one location on a sheet of paper to another. Perhaps most frighteningly, a higher-dimensional being could rip us right out of our 3D reality into the incomprehensible fourth dimension. And somehow, I'd want to know what that experience is like!

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. Image credit: © 2007-2016, Max Planck Institute for Gravitational Physics, Potsdam.

From Sinisa Lazarek: "I still haven’t read the paper, but reading the article, the first thought I got is that this might end up like “turtles all the way down”. If we assume that this is true, the question comes up of how did the BH in +1 dimension come to be in the first place? Is there a 5d universe that needed to begin and evolve to the point of having 5d BHs in order for one to create our 4d universe? Then before that a 6d one to create a 5d one to create a 4d one to create a 3d one?"

This is true! If our Universe came from a higher-dimensional black hole and our black holes give rise to lower dimensional Universes, couldn't this go on ad infinitum? And the answer is no, in the sense that there is a lower limit and an upper limit. If there are "truly" 10 or 11 or 26 dimensions in total, then that's where the initial existence we wonder about has to originate. And you can't go into negative dimensions; a 0D reality is just a point, and that's the smallest we can go. So there are a lot of turtles, but at some point, there's a non-turtle foundation and a "highest turtle" at the top.

From eric on searching for aliens with neutrino signals: "How hard is detecting a neutrino signal when there’s a noise source 10x higher? How much money/time would need to be spent in tech development to get there? I don’t know."

So, this was the graph I posted, and I'm surprised that no one realized the important component of why reactor anti-neutrinos are so powerful as a source for alien civilizations:

In the energy range above 10 MeV, there is no greater source of antineutrinos in the Universe than from deliberately built nuclear reactors.

Supernova bursts undergo nuclear fusion, where protons and electrons fuse into neutrons... and neutrinos, not antineutrinos. Terrestrial sources (i.e., from planets) fall off very rapidly above about 6 MeV. And the cosmological neutrino/antineutrino background is catastrophically low in energy, and doesn't play a role. So that's why: reactor anti-neutrinos, which you can detect by their energy spectrum, are a surefire non-natural signal of deliberate activity in the Universe.

And finally, from Julian Frost on the detectability problem: "Suppose (for argument’s sake) that there was an advanced civilization on a planet orbiting one of the stars. Suppose that this civilization detected Earth, and decided to send a signal after first working out its track. Even if they correctly aimed the signal, and even if our antennas were turned in the right direction at the right time, by the time it arrived it would be so weak that we would need to be extremely lucky to pick it up."

You don't have to go very far to run into problems of transmission power and how massive or sensitive your dish/antenna needs to be to pick it up. There are fewer than ten observatories capable of picking up the data transmitted from New Horizons, just past Pluto, which is around 0.00059 light years away from Earth at the moment. The data transmission rates are lousy; it will take a total of ~16 months to transmit all the information that New Horizons gathered in just a few hours around the Pluto/Charon system.

In other words, they would need to be transmitting that signal with a lot of power for us to have a chance to pick it up. Collimating a "pencil beam" as well as one can doesn't change the fact that flux dissipates as the inverse distance squared, so traveling 10,000 times as far means a drop in the power you receive of a factor of 100,000,000.

It isn't prohibitive, but it sure is a large constraint on what we could detect from an alien civilization. If you want to go with electromagnetic signals, you sure do have some obstacles to overcome! Thanks for a great week, and see you back for another spectacular one -- starting tomorrow -- here on Starts With A Bang!