“A journey is a person in itself; no two are alike. And all plans, safeguards, policing, and coercion are fruitless. We find that after years of struggle that we do not take a trip; a trip takes us.” -John Steinbeck
Here we are: the final Comments of the Week of 2014 here at Starts With A Bang, a year that’s seen a tremendous number of changes, achievements, struggles and triumphs. This past week has perhaps been a microcosm for the entire year, with articles on cosmology, a new Monday series, a guest post and more. If you missed anything, here’s what we’ve covered:
- Dark matter vs. dark energy (for Ask Ethan),
- The eclipse of a lifetime is coming (for our Weekend Diversion),
- Genesis episode 2, our Solar System (for Mini-Movie Monday),
- The rising star of science (another great post by Sabine Hossenfelder),
- Fixing Occam’s razor, and
- The Christmas tree cluster (for the holidays).
You’ve had some interesting things to say, some of which was interesting, some of which was unexpected, and some things, in particular, that call for a response. I hope I won’t let you down on this edition of our Comments of the Week!
From Omega Centauri on the unbound structures in our Universe: “Presumably any ordinary matter still in the underdense regions will never form stars or galaxies. Do you have an estimate of what fraction of the ordinary matter participates in galaxies, and intergalactic gas within galaxy clusters. If you postulate a purpose for the universe is to make galaxies, then this fraction would be considered to be the (matter) efficiency of the universe. Is it much less than 1?”
It’s easy to look out at the galaxies — the brilliant sources of light in the heavens — and guess that’s where the Universe’s mass and energy is. But what we’re seeing is the stars alone: some 0.5% of the total mass within galaxies. What’s even stranger than that, perhaps, is that we believe that the majority of matter in the Universe isn’t even bound within galaxies, but rather exists as part of the intergalactic medium! There was a great paper about a decade ago (here) on the cosmic energy inventory, where they went through not only how energy was broken down in the form of dark energy, dark matter, normal matter, neutrinos and radiation, but broke down the normal matter into all its known components. Here is the summary of results for normal matter, as you requested.
This is still pretty accurate, and — as you can see — about 6% of the total baryons are in the form of stars, about 2% in the form of neutral gas, but the biggest number is that about 90% of the baryons make up the warm, intergalactic plasma.
Of this, about 60% is found in the virialized region (i.e., gravitationally bound) around galaxies, and about 40% is found in intergalactic space, completely unbound to clusters. According to this work, about 36% of the total matter is then found outside of any bound structure. This is roughly consistent with the 40-50% figure I’ve seen recently from other sources. But yes, the “matter efficiency” of the Universe, as you call it, is significantly less than 1.
From George on the eclipse of a lifetime: “Furthermore those lucky enough to be able to get to Illinois can return seven years later to exactly the same spot and watch the 2024 total eclipse. Now that’s a rare opportunity.”
You know, I try hard to avoid both a northern hemisphere and a USA-specific bias, but I know I can’t help myself sometimes. When it comes to total eclipses, we’ve really been unlucky (as far as luck has anything to do with it) over the past few decades, which, you know, makes up my lifetime so far. The last total solar eclipse to occur over the contiguous United States was way back on February 26, 1979, when I was six months old. I had an 88% partial eclipse when I was a teenager that was really interesting (light but not heat from the Sun! Bizarre shadows! Seeing it directly with eclipse glasses!), but not a lot of opportunity for another experience since. That all changed two years ago, when I went on an expedition to see my very first annular eclipse, and it was a spectacular occurrence.
So you’ll have to pardon my excitement, but our drought will extend to 38 years in advance of this 2017 eclipse, but then we get five in a 35-year span: in 2017, 2024, 2044, 2045, and then once more on March 30th, 2052. (With a little luck, I will still be around at 73 for that one.) So it is — for pretty much anyone in the USA who’s my age or younger — our first real chance to experience a total solar eclipse. While being in southern Illinois means you won’t have to move to see it, moving around is a small price to pay to go and hunt all five!
From Armando on our Solar System’s origins: “How do moons arise and what exactly defines a moon?”
Briefly, there are three ways:
- You can be a gravitationally captured body — either an asteroid or a Kuiper belt object — by a planet.
- You could have formed from an early-stage disk around a larger world; this is where the gas giants’ moons predominantly come from.
- Or, you could have formed from a rare, catastrophic collision in the early Solar System.
That third one, mind you, is where we think our own Moon comes from, and — I promise — will be the topic of a future mini-movie Monday!
From zav, who has a strong opinion about my personal appearance: “Geez, Ethan looks like a freak. It’s hard to take someone who looks like that seriously.”
One of the unfortunate consequences of putting yourself out there in the public eye is that you’re going to get comments like this. You’re going to get people who won’t judge you by the quality of the content you produce, by your merits or lack thereof, but rather by their own opinions of what someone in your position ought to look like, by some arbitrary standard.
Let me say it unequivocally: I have nothing to be ashamed of when it comes to my appearance. I am proud of who I am and how I present myself to the world, and if you can’t accept me in the role of whatever it is that I choose to do because of my appearance, I strongly suggest you look inwards, and ask yourself why that is. Perhaps you should reconsider how you judge people based on the way they look; you never know who just might turn out to be exactly the kind of person you’d hope to see more of in your life.
From daedalus2u on Occam’s Razor: “I would be surprised if there is not life on Mars. It likely won’t be found on the surface, but until there have been holes drilled deep enough into Mars that temperatures above 150 C are reached, in multiple places, I would not dismiss the possibility.”
It’s very difficult to gauge just what we’re looking at from a sample size of one: that is, we have one place in the Universe where we know life exists, and many places in the Universe where we know the ingredients for life exist, yet no surefire evidence that life is there. I think it’s important to look, and I think it’s important to be open to the possibilities that what exists elsewhere may be extremely different from life on Earth, or what we imagine that life elsewhere might look like.
But let’s also not claim that any signature that could just as easily be due to geologic or inorganic processes is an indicator of life. We’re talking about methane, something produced in copious amounts inorganically all over the place. (Hello, Titan, anyone?) Yes, it could be a sign of life, but why one would think that was a likely option given what we know, that I don’t understand.
And finally, from Sinisa Lazarek on the Christmas Tree Cluster: “Dear Universe, please don’t send any high energy jets toward us in 2015, otherwise it’s all great! “
Please, don’t go away just yet; there’s another great week of Starts With A Bang to enjoy before the new year. I promise, I’ll make it worth your while!
Have a great weekend, thanks for a great set of comments, and I’ll see you back here (hopefully very) soon!