“For in the final analysis, our most basic common link is that we all inhabit this small planet. We all breathe the same air. We all cherish our children’s futures. And we are all mortal.” -John F. Kennedy
After a great week over on the new Starts With A Bang blog, where we covered a whole slew of topics like:
- Long Term Timekeeping (for Ask Ethan #30),
- The Amazing Lives of Coral Reefs (for our Weekend Diversion),
- The Biggest one of them All, M87 (for Messier Monday),
- Why are there (at most) eight planets in our Solar System?,
- The Multiverse is not the answer, and the great long-read,
- Global Warming for Beginners (for Throwback Thursday),
and you weighed in here with your comments, with some really excellent discussions arising, particularly on the Multiverse post. Let’s dive right in, and take a look at your Comments of the Week!
From Truthspew on the topic of Long Term Timekeeping: I would think if they brought an atomic clock on board with them the time would still be earth based but what we’re used to doing.
You see, it’s be fantastic if we could keep time for arbitrary lengths using atomic clocks. Indeed, they’re far more accurate than any natural clocks, including millisecond pulsars or radioactive decay times. But although that’s a brilliant idea in principle, there’s a wrench in the works when it comes to practicality.
Atomic clocks require a lot of power to continuously stimulate atomic transitions, and a lot of cryogenic fuel to keep the atoms at ultra-low temperatures. Not such a big deal when you’re talking about doing this in a continuously powered laboratory on Earth, but that’s a lot of resources to devote to keeping a simple clock running. The mechanism I gave in the original article — counting atoms or looking at a pulsar — has the advantage that all you have to do is look once at the beginning and once at the end, and requires no devoted power in the intermediate time. If you can figure out a way to do that with atomic clocks, I’ll happily revise my answer! (Also, you’ll probably win a Nobel Prize along the way, an arguably greater accolade.)
From Colin Burgess on the subject of the number of planets in the Solar System: Why did the asteroid belt form at the frost line, rather than another frozen planet/s? Is there something special about the asteroids straddling this line, that caused an inability for planet formation?
It seems like that would be the dichotomy, doesn’t it? Why do we have a belt of asteroids instead of a planet there? As it turns out, having a planet at the Solar System’s frost line is probably an extremely rare occurrence, while having asteroids at that location ought to happen in the majority of Solar Systems. The key comes down to what the “frost line” actually means.
Inside of the frost line, solid hydrogen-based compounds like water, ammonia and methane cannot exist; the temperature and energy flux from the parent star is too high. Planets land where they land during Solar System formation, but so long as no giant planets have migrated from outside the frost line to inside (disrupting the belt), there will be leftover material at the frost line and beyond. And unless you happen to live in the rare star system that happened to form a planet right at the frost line, you’ll expect there to be an asteroid belt until you near the vicinity of the first giant planet outside the frost line.
We normally think of our asteroid belt as a “belt”, but in reality, its component asteroids span from about 2 AU to 3.3 AU, with a total of just 4% the mass of our Moon. There simply isn’t enough material there to make a planet, and this is the case in the vast majority of Solar Systems.
From David L as respects The Multiverse is not the answer: Is there any reason to suspect [other Universes] would be “like” our own? Would what we consider universal constants have to be the same there?
You must remember that our Universe is all we have access to. What the CMB spectrum of fluctuations and the BICEP2 results tell us about inflation is that it occurred at an energy of ~a few × 10^16 GeV, which is well below both the Planck energy and the (hypothesized) string scale. We know — from observations of our own Universe — that having the Universe up at this scale and then allowing it to have inflation end and a Hot Big Bang ensue cannot result in different fundamental constants. The possibility of universal (sic) constants having different values relies on the dual assumption that there are inflationary regions that had much greater energies than where our Universe was just prior to the end of inflation and also that those energies would allow the possibility of falling into a different low-energy state than our own. Yes, it’s possible, but there’s no compelling reason — either theoretical or experimental — to suspect that this is true.
From Tom Campbell-Ricketts on The Multiverse is not the answer: I have tried to investigate what types of anthropic reasoning are valid, but I confess, the problem is difficult, and I’ve not found a satisfactory answer.
You know, I have no problem when anthropic reasoning is used as sort of a self-evidence sanity check for the Universe. As I’ve said before:
The laws of nature must be such that the Universe can exist in a fashion consistent with what it is observed to be.
The presence of carbon in the Universe tells us there must’ve been a mechanism for carbon to be created. The existence of galaxies and planets tells us that the cosmological constant must’ve been small enough to allow for the formation of galaxies and planets. But anthropic reasoning is only interesting in a scientific sense if it can point us towards a direction that helps us understand how the Universe came to be the way it is. Without that caveat — without a testable prediction to explore — there may still be other philosophical or mathematical reasons to take an interest in what anthropics can tell you, but it’s not scientifically interesting.
From veyd on Global Warming for Beginners: [W]hile i’ve long accepted that rising climate temperature is an ongoing and scientific fact, it’s also been a long time since i had any interest of reading any more about it. [I]’m not an activist and there is not very much we can do as individuals about this. [S]o i was going to skip this one too, but the explanation involving the planets was such an interesting twist, [I] just had to read on.
One of my favorite things about science is that it’s such a rich store of human knowledge that if you ask 100 experts in a field to tell you the story of some aspect of their field, you will get 100 different versions of the same story, and — so long as they stick to the known, conclusive science and don’t resort to their own pet speculations — they’ll all be consistent with one another. I’ve never claimed to be the expert on anything and I don’t fancy myself to be one, but I’m fortunate to be enough of an expert on some facets of science that I can tell you the story as it makes sense to me. I can show you the threads that come together to form the tapestry, and, if I’m doing it right, you can see the same picture I do at the end of it. I’m happy to have you along for the journey, and many of you are providing me with valuable perspectives on how you make sense of things.
Cheers, and thanks for another great week!