“We have finally established the contours that define the supercluster of galaxies we can call home … This is not unlike finding out for the first time that your hometown is actually part of much larger country that borders other nations.” -Brent Tully
It’s been another remarkable week here at Starts With A Bang! Full of science, stories and a slew of information you won’t find anywhere else, we’ve hit on a number of fantastic ones for your perusal. The news you haven’t heard? My upcoming book, on the real-life science behind the technologies envisioned by Star Trek, now has a listing on the publisher’s website! If you missed any of the science we’ve covered, take a look back at all of it:
- If gravity attracts, how can the ‘dipole repeller’ push the Milky Way? (for Ask Ethan),
- Black hole caught devouring star for an entire decade (for Mostly Mute Monday),
- This is what would happen if an asteroid hit New York,
- The strangest eclipse fact of all: the Moon’s shadow isn’t a circle,
- The first galaxies: what we know and what we still need to learn, and
- Why science will never know everything about our Universe.
A week from Monday, I’ll be delivering a public talk at 7:30 at OMSI on February 20th on the controversy over the expanding Universe. If you can make it to Portland, OR, don’t miss it! I also had an appearance on Rochester public radio, and I’m particularly pleased with the latter half, where we discussed expertise. Now, with all that out of the way, you’ve had a lot to say, so let’s get right into our comments of the week!
From Michael Richmond on advances in telescope cameras: “Ethan, you state that we can use photomultiplication to detect 20% of the incident photons. Well, we can use photomultiplication, it’s true, but the best CCDs these days can record of order 80% – 90% of the photons which strike them, without photomultiplication.”
This is outstanding! For those who don’t know, Michael Richmond is an observational astrophysicist at R.I.T., and a much better expert than I am on those matters. This highlights a problem when you ask someone with lots of expertise but not necessarily the most expertise: you’ll get an answer that’s incomplete, out-of-date or otherwise insufficient. Even if you know your information may be out of date and you go looking for better things, you may not find it. Be open to new information, to improved conclusions or analysis you may not have heard of, and to updating your conclusions. Even about the issues you feel most strongly about. The world is changing. Knowledge is growing. And if you don’t keep up, you’ll get left behind.
Thanks for catching me up, Michael.
From Denier on the issue of rights: “I believe this [referring to my statement that ‘I am starting to think that you and I have very different views on what a “right” is, and that may be the root of where we differ on oppression as well.’] to be an accurate statement. A “right” is a legal entitlement. My interpretation of the First Amendment is along the same lines as the ACLU’s. You’ve admitted in the past that you don’t really understand it as it is not your field of expertise. No problem. A lot of people can’t back up any of their positions with any sort of substance.”
What I’ve admitted, for clarity, is that I don’t understand the modern legal interpretation of the First Amendment. It was a link that someone (Narad? eric?) provided to popehat that was very informative concerning where — as above — my understanding was way out of date. Rights are far more extensive than the first amendment, however. Note the rest of the constitution, the other amendments, and all the court rulings that reflect that. If you want some substance about where I get my concept of rights from, it was from studying Thurgood Marshall. For example, read this:
“What is striking is the role legal principles have played throughout America’s history in determining the condition of Negroes. They were enslaved by law, emancipated by law, disenfranchised and segregated by law; and, finally, they have begun to win equality by law. Along the way, new constitutional principles have emerged to meet the challenges of a changing society. The progress has been dramatic, and it will continue.
The men who gathered in Philadelphia in 1787 could not have envisioned these changes. They could not have imagined, nor would they have accepted, that the document they were drafting would one day be construed by a Supreme Court to which had been appointed a woman and the descendent of an African slave. We the People” no longer enslave, but the credit does not belong to the Framers. It belongs to those who refused to acquiesce in outdated notions of “liberty,” “justice,” and “equality,” and who strived to better them.
And so we must be careful, when focusing on the events which took place in Philadelphia two centuries ago, that we not overlook the momentous events which followed, and thereby lose our proper sense of perspective.” -Thurgood Marshall, 1987
Note that this is a strong argument against constitutional originalism, and is one instead in favor of Marshall’s “living document” approach. The idea is not that “laws give you rights” but that people have rights, inherently, and it is the responsibility of the legal system to lift those rights out of the laws that are written. Now, I don’t expect you to agree with Marshall or with me, but let’s not pretend that scientific expertise — matters of true and false — are the equivalent of legal expertise, which are not.
From Dr. Hazel-Connie Low Chi Leong on the two contributions to a galaxy’s recession speed: “According to this article, galaxies are moving apart from each other. This article talks about the speed that galaxies are moving apart from each other. […] This speed depends on two factors: 1.)The FIRST factor discovered by scientists: Force of explosion caused by the “Big Bang”. 2.)This article talks about a second factor: Mass of Galaxy. […] A large part of the speed of the recession between two galaxies is the speed caused by the force of the Big Bang. This SECOND FACTOR DOES EXIST!,……BUT the speed calculation answer change is relatively insignificant. It just makes the answer more accurate.”
Here’s the deal when it comes to a distant galaxy: it’s not quite “the force of the Big Bang” but rather the physics of the Universe’s expansion. This is driven by initial conditions at the Big Bang, but also by the matter, radiation and dark energy content of the Universe. On the largest scales, this effect dominates. And by “largest”, I mean scales of about 100 megaparsecs (~326 million light years) or more. Those scales are way larger than galaxy scales. On smaller scales, gravitation dominates. The galaxies within a cluster can move at relative speeds of thousands of kilometers-per-second, and that is hugely important. Hubble’s original graph, above and to the left, is entirely dominated by peculiar velocity.
Only on the largest scales can we neglect peculiar velocity, or the effect of masses on the local Universe and the galaxies within it. The whole point of the dipole repeller concept is that on scales of our local supercluster, you cannot neglect this term, and the void in the direction opposite to Laniakea is exactly what we need to account for the hitherto unexplained peculiar velocity.
From MobiusKlein on breaking the limit of black hole accretion: “Can you expand on the ‘faster than the Eddington accretion limit’ part?”
The way Eddington limits work in general — and this started for stellar luminosity — is that you can imagine a star is a combination of two things: fusion in its core generating an outward radiation pressure, and the gravitation of its full mass holding it together. The Eddington limit basically says, “if you go past this mass, the radiation pressure will be greater than the gravitational force at the surface, and so the mass will drop back down and the outer portions get blown off.” Simple enough, right?
Only, you can add additional parameters in: rotation, angular momentum, or you can have a temporary condition! For the Eddington accretion limit, that’s just a luminosity derived from the matter falling into it. But there is an unknown parameter in that Eddington limit equation, and it is a parameter that cannot be measured. (It’s epsilon, the fraction of the gravitational potential energy radiated away.) If that number turns out to be small, the Eddington rate (which has epsilon in the denominator) could turn out to be tremendous. So that’s the elaboration! And if you want more, Garret Cotter of Oxford has some lecture notes on this here.
Yes, there has been a binocular-only (i.e., telescopes can see it too, but not the naked eye) comet this past week in the sky! It has a spectacular tail, a green coma, and it’s a wonderful object if you have clear skies and know where to find it. The comet is named comet 45P/Honda-Mrkos-Pajdusakova, after it’s three co-discoverers in the 1940s, and it appears to originate from the asteroid belt. There’s not very much that’s unusual about this comet, despite what others are saying, but it’s always a treat to get to see one. If you have clear skies and the right equipment, go for it!
From Sinisa Lazarek on the Moon’s eclipse shadow: “don’t think it’s strange that the shadow is ellipse since everyday experience shows you that.. one ball casting shadow on another ball”
This is right, and was one (the first) of the three big points I made. The thing that’s strange is that from our vantage point on Earth, all of the shadows we see of worlds on other worlds appear to be circles. This is a visually awesome and impressive phenomenon.
But don’t let this visual effect fool you, as Sinisa correctly points out! What might appear to you to be a circle from afar belies the fact that the surface of these worlds are actually curved, and what you’re seeing is a two-dimensional projection from a very particular perspective. If you were to look at the shadow on the (curved) surface of the world itself, it would be stretched by that curvature, and hence would appear elliptical or elongated in some fashion. Hence, not a big surprise, but you haven’t to think about that effect too!
From Wow on why science won’t know everything about the Universe: “And that’s well outside science, since science is about the discovery of the processes in the real universe. So doesn’t tell you about maths, or logic, or even language. Despite it being fairly core to the process of science.
At the moment, it looks like there are some known unknowable unknowns. And there’s no reason to suspect there aren’t more.”
All of this is true:
- Even if every particle in existence was known and measured to an arbitrary accuracy, much about the past and future would still be unknowable.
- Even if everything about our observable Universe’s past and future were known, there is still the unobservable Universe which goes beyond our own.
- And even if we knew all about the unobservable Universe, there’s still a region of time — before the Big Bang — that contains information that is unknowable, and appears irrelevant for all the things we can observe.
That doesn’t mean it isn’t worth investigating or theorizing about, but it does mean that there are both inherent uncertainties (when an electron and positron annihilate, which direction will their photons go off in?) and inherent unknowns (beyond the causal horizon? before anything impacting our Universe today was around?) that limit what we can ever know.
From eric on the possibility that these barriers may someday be overcome: “Its certainly possible that we develop new theories that tell us about the pre-inflationary period and make other testable, separable predictions. We can then gain confidence in one over the other by testing the bits of those theories open to us.”
It is possible, and many are trying. What I’ve asserted, above, is only true if our present best theories about the Universe are true; they may not be. There may be some other, more fundamental truth, and it may wind up meaning that some of the inherent problems I listed aren’t inherent problems at all.
But that doesn’t change the original fact of what I wrote:
“The total amount of information accessible to us in the Universe is finite, and hence, so is the amount of knowledge we can gain about it. There’s a limit to the amount of energy we can access, the particles we can observe and the measurements we can make. There’s a whole lot left to learn and a whole lot that science has yet to reveal, and many of the present unknowns will fall in the near future. But some things we will likely never know. The Universe may yet be infinite, but our knowledge of it never will be.”
From Jimmy Couch on nothingness: “You talk about “nothing” being a completely and utterly NIL state of being. No energy, matter, anti-matter, time…..absolute, total, physical(being defined as ANYTHING labeled by physics) nothingness. […] Nothingness means a completely static state of non being. If there is nothing there, there can BE no energy…”
One of the points I’ve made repeatedly, but I don’t mind making again, is that there is a distinct difference between what “nothingness” means in our Universe (i.e., to a physicist) and what it means in our own conceptual minds (i.e., to a philosopher). In our Universe, there are some Universe-defining things that still exist: spacetime and the laws of physics. In our minds, we can take that all away, but in the Universe, we can’t.
If you take away time, then how does something “come into existence?” There’s no “cause” or “effect” or “before” or “after” if there isn’t time. If you take away space, how can you distinguish between existence (which needs a place to exist) and non-existence? And if you take away the laws of physics, then you’re not talking about anything relevant to the one special case that physicists care about: our Universe.
You may like your definition of nothingness — a completely static state of non-being — but it doesn’t make physical sense. You are welcome to entertain it all you like, to think about it, to philosophize about it, to infer theology from it, etc. But it’s a non-starter to a scientist. Your definition is irrelevant to the real Universe.
And finally, from John on what’s now become a 1000+ comment thread (the original firestorm-starter): ”
[Ethan:] “Science can never prove or disprove the existence of God, but if we use our beliefs as an excuse to draw conclusions that scientifically, we’re not ready for, we run the grave risk of depriving ourselves of what we might have come to truly learn.”
Thanks. That – all of that – needs to be said and stressed more often”
There are two ways I can generally categorize a “search for God,” as it were. One is to look at the question as being completely outside of the realm of what’s knowable about the physical Universe. To place God in the realm of fully outside the natural Universe we experience. To put that concept alongside the other unknowables like “where did spacetime originate,” “where did the laws of physics come from,” “did the Universe have a beginning or is it eternal,” and so on. (If these questions become answerable, i.e., if they ever come into the realm of scientific inquiry, God will either be discovered or will be pushed out.) That’s fine by me; we have questions that are unanswerable in principle, and looking beyond what science can address is a find way to raise possibilities, albeit without a test, none are compelling.
The other is to use God as a placeholder for any presently unknown or unexplained phenomenon. A “God of the gaps.” What a small God to have! A God that can be (and likely will be) squeezed out into non-existence simply by discovering more about the natural Universe is a God that is just screaming to be disproved. Indeed, a great many Gods (and stories about Gods) have been scientifically disproved in exactly this fashion, although proof is not necessarily enough for its believers.
I won’t tell anyone what to believe, but as soon as your belief causes you to divorce yourself from reality, I’m going to be there doing my best to inform you — and the whole of humanity — about what our physical reality actually is. Because we know what physical reality is, and no amount of belief is going to change it. There may be many powerful people claiming that “we live in a post-fact world,” but the world itself tells us otherwise.