news sciences: Comments of the Week #84: From the very, very end to Mars’ lost atmosphere [Starts With A Bang]

“It is better to have your head in the clouds, and know where you are… than to breathe the clearer atmosphere below them, and think that you are in paradise.” -Henry David Thoreau

Every week at Starts With A Bang is special, but we made an amazing move, over to Forbes, which is the new home of our blog! Starting on November 2nd, we made our move, and as the month unfolds, we’ll be bringing all-new content over there, to be republished (ad-free) on Medium the next week. Here’s the good stuff, just in case you missed anything:

The very, very end of the Universe (for Ask Ethan),
I’m going to be AXE COP! (for our Weekend Diversion),
Move Over Hubble, Gravity Itself Is The Best Cosmic Telescope Of All (Mostly Mute Monday will return next Monday),
Jupiter May Have Ejected A Planet From Our Solar System,
Keeping Better Time With Atomic Clocks (a live-blog event with nobel laureate David Wineland),
This Is The Largest, Most Massive Distant Galaxy Cluster Ever Discovered,
and Mystery Of Mars’ Lost Atmosphere Solved At Last, Thanks To NASA’s MAVEN Mission (sorry, Throwback Thursday fans; that official series is ending).

As always, I’m happy to bring you the best of the comments from this past week, and know that starting next week, I’ll be going back two weeks rather than the standard one in order to make sure that any follow-up comments that need attention get exactly what they deserve. That said, let’s jump on in to your Comments of the Week!

http://ift.tt/1NWs7Zn

From James Carlson on the Big Rip scenario: “It could be that entropy doesn’t play to a full house in that the big rip might serve to recreate the universe in a sudden expansion of spacetime and the creation of sub atomic oaricles.”

There are a lot of misunderstandings about both entropy and the Big Rip, and this combines the two. Entropy, to be clear, is a measure of how ordered or disordered a system is. It can stay the same or increase in a closed system, but never appears to decrease. However, the expansion of space (or spacetime) and/or the presence of a particle-creating phase transition (which is what I assume you meant) in no way either recreates the Universe or violates what we know about entropy.

Image credit: Universe-Review website.

However! The “Big Rip” does not necessarily mean that the Universe gets ripped apart into oblivion, just as a “Big Crunch” doesn’t necessarily mean that space and time disappear and get swallowed up into nothingness. While a crunch could lead to a “bounce” and a cyclic scenario (above), the steps up towards a rip — and hence to higher intrinsic spacetime energies — could lead to a phase transition that give rise to a new hot Big Bang: a rejuvenated Universe. This theory hasn’t gotten a lot of attention, but it was put forth by physicist Eric Gawiser about 15 years ago, and it remains an intriguing possibility. Keep it in the back of your mind when you think of the Big Rip.

Image credit: NASA / STScI / Ann Feild.

From Denier on the very, very end: “Maybe it is just me, but I’m thinking you are not going far enough in the future. The cosmic rate of expansion is ever increasing. It could very well get to the point where even the strong nuclear force is overwhelmed by the rate of expansion. It will be like a black hole in every direction and all the data that was ever in the universe is gone. That includes whatever you did. Merry Christmas everyone!”

But the cosmic rate of expansion is not ever increasing. Don’t confuse the phrase “the accelerating Universe” with the (incorrect) statement that “the expansion rate is increasing.” The expansion rate — the Hubble rate — is not increasing. It is not observed to increase; in fact, it is decreasing right now! Its present value, about 70 km/s/Mpc, will drop to an estimated 45-50 km/s/Mpc, where it will asymptote. Then it will remain at that rate forever; that’s what a cosmological constant predicts.

The individual galaxies that are unbound from one another, however, will speed up as they move away from one another. The galaxies of the Virgo Cluster, for example, moves away from us right now at around 1,200 km/s. As time goes on, they will move away at 2,400 km/s, then 4,800 km/s, then 9,600 km/s… and after enough time, they’ll be receding faster than the speed of light! This is due to the expansion of space, of course, but not due to the expansion rate increasing. And hence, unless dark energy increases in strength — unless it’s not a cosmological constant — we’ll never have that Big Rip or dark energy overwhelming any of the forces. So there are many more Merry Christmases ahead. We think.

Image credit: E. Siegel and family, Halloween 2015.

From Julian Frost on Axe Cop! “Ethan, you used to change your picture up top when you had a new Hallowe’en costume. Last year, you were a manotaur, but you didn’t change the picture. Are you going to change your picture this year?”

Ugh… fine, Grey Diamond, you can tell your story.

I mean, I think I can handle that. It’s a good idea, and it’s done. I’ll chop your head off!

Image credit: Jerry Coyne via http://ift.tt/1NWsaUT.

From eric on Halloween costumes: “Great costume. Saw this on Jerry Coyne’s site and thought to myself “hey, maybe a costume for Ethan for 2016?” Paint your limbs purple and wear and awesome hat!”

So what you’re saying is, you want to see more Ethan genitalia on this site? Let’s… uhh… not exactly take a vote on that. I appreciate the sentiment — really I do — but the ship has kind of sailed on that one.

Image credit: NASA / Dana Berry.

From See Noevo on the disfavoring of the Nice Model: “I’m assuming the “Nice Model” that was disproved was the latest consensus model, which replaced other models which had been disproven, or at least shown to be less satisfactory than “Nice.””

First off, it’s the Nice model as in Nice, France, or NEESE, not the “Nice” model as in “Nice head, I think I’ll take it.” The issue is that in most simulations — and that’s the only way to adequately understand a system as chaotic as planet formation — you form large, giant worlds in the inner Solar System, which we have exactly none of. So that’s the difficult thing to explain. The Nice model did an excellent job of modeling how the gas giant world could have wound up in their current configuration, conveniently explaining how the inner Solar System was “cleared out” of giant worlds.

Image credit: Wikimedia Commons user AstroMark, of one realization of the Nice Model.

Well, partially. It was an idea proposed in 2005, and it gave rise to the Grand Tack model in 2011/2012, which is where the “ejected giant (or two)” idea came from; it seems to work better. But for all of it, it requires Jupiter migrating through the inner solar system. And if that were the case, it would have ejected Mercury and Mars with near certainty, which means that some or all of the rocky, inner planets likely formed after the Jovian migration. This changes the timescale of the solar system, and means the late heavy bombardment did not arise from Jupiter moving outward through the asteroid belt.

That’s how the science has changed; it’s a learning, revising-as-we-go experience. Stick around, this is in many ways the best part of the ride!

Image credit: NASA / GSFC.

From CFT on science denial: “I would point out your very use of a term like ‘science denier’ to describe someone who does not agree with you for whatever reason is as vulgar as calling them an infidel. ‘Denier’ is a term used by a true believer or zealot in a matter of faith or religious inquisition, and is completely inappropriate coming out of the mouth of a scientist.”

I take it that you haven’t been working as a scientist in the field of science communication, professionally, for many years as some of us have. If you have, you’re very likely to run across the same types of arguments over and over, couched in different words or phrases, but with the same discredited themes and conclusions.

You’re likely to see the same deliberate mistakes, the same dissembling, the same techniques (Gish Galloping), the same Zombie arguments… in short, the same denial tactics. Now there are some honest people who are open to assimilating new knowledge, to revising their opinions, and to learning new things in general and then changing their conclusions accordingly, and I agree that labeling them with a negative term that puts them on the defensive doesn’t do any good.

But I also feel lots of sympathy for those who work so hard to put the valid information out there who are simply met — over and over — with the same stubborn resistance to facts, reasoning and the quality science that’s out there. What you are doing is known as tone policing, and it’s a known and common tactic to divert attention away from the real issue: that someone is demonstrably wrong in their assertions, and yet their assertions serve to misinform a large segment of the general populace. For my own part, I strive to get the correct information out there in as honest and kind a fashion as possible, but I also strive to really control only my own actions, and to restrain myself in moderating comments. (And responding to them, too.) All of that is to say, this: I hear what you’re saying, but I’m not sure I 100% agree.

Image credit: NASA / GSFC.

And finally from Narad on the loss of Mars’ magnetic field: ”

However, at some point less than a billion years after Mars formed, its global magnetic field ceased to be, removing the planet’s main source of protection from the solar wind.

Is there a current explanation for how this happened?

Giant impactors appear to be out in front (PDF).”

It’s an interesting theory, and it’s certainly one that’s gotten the most attention as of late, but I don’t know that it’s the leading theory. Mars is small, and by small, I mean it has only a few percent the mass of the Earth. Its volume is much less than Earth’s, while its surface area is only marginally less; combine those two factors, and Mars loses its heat twice as quickly as Earth does. If you throw in the fact that it has less heating to begin with (due to less gravitational contraction and fewer radioactive materials in its core), and the Martian core could have — with no external factors — completely lost its dynamo properties in only ~500 million years.

Image credit: Fahad Sulehvia http://ift.tt/RAW5pU from Science magazine, October 11, 2013.

There could have been other factors at play, though. I just want to point out that I don’t think giant impactors are universally favored, nor do we have evidence for a giant impact with Mars in the cratering record or elsewhere in Martian geology. It’s possible, but “out in front” is kind of a stretch at this point. I think it’s important to be honest about how large our uncertainty is at this time.

And with that, we come to the close of our week. Thanks for joining me, and if you’ve got suggestions for what you’d like episode two of our Podcast series to be, drop us a line and let us know!

from ScienceBlogs http://ift.tt/1MqBeC9