Event Horizon Telescope – Cosmic Reflections

Keith Bechtol at UW Space Place

We are so very fortunate here in southern Wisconsin to have evening public lectures the 2nd Tuesday every month of the year at the University of Wisconsin Space Place, expertly organized by Jim Lattis. On Tuesday, November 12th, Clif Cavanaugh (retired physics and astronomy professor at the UW in Richland Center) and I made the trek (as we often do) from Spring Green-Dodgeville to the Space Place in Madison. This month, we were treated to an excellent presentation by Keith Bechtol, an Observational Cosmologist in the Physics Department at UW-Madison. His topic was The Big Picture: Science with Astronomical Surveys. Keith is an early career scientist with a bright future. His presentation was outstanding.

I’d like to share with you some of the highlights.

Before the talk, which is mostly about the Large Synoptic Survey Telescope (LSST), currently under construction in Chile and expected to see first light in 2020, I asked Keith about whether LSST would be renamed the Vera Rubin Telescope as was announced at AAS 234 in St. Louis this past summer. As it turns out, Keith has been a vocal advocate for naming LSST after Vera Rubin, though no final decision has yet been made.

Before I get into notes from the talk, I wanted to share with you the definition of the word synoptic in case you are not familiar with that word. The Oxford English Dictionary defines the word synoptic as “furnishing a general view of some subject; spec. depicting or dealing with weather conditions over a large area at the same point in time.” But rather than the traditional meteorological definition, here we are referring to a wide-field survey of the entire night sky visible from Cerro Pachón in Chile, latitude 30˚ S.

Keith first talked about how astronomical imaging is currently advancing along two fronts. The first is high-resolution imaging, as recently illustrated with first image of the event horizon of a black hole from the Event Horizon Telescope, where an amazing resolution of around 25 microarcseconds was achieved.

In general, the larger the telescope aperture, the smaller the field of view.

The Hubble Space Telescope’s Ultra Deep Field is only 3.1 arcminutes square

A survey telescope, on the other hand, must be designed to cover a much larger area of the sky for each image.

Not only can a survey telescope detect “anything that changes” in the night sky, but it also allows us to probe the large-scale structure of our universe. Three still-mysterious entities that are known to affect this large-scale structure are dark energy, dark matter, and neutrinos. Keith indicates that “these names are placeholders for physics we don’t yet fully understand.”

Dark energy, which is responsible for driving galaxies apart at an accelerating rate, is unusual in that it maintains a constant density as the universe expands. And its density is very low.

Supernovae are a very useful tool to probe the dark-energy-induced accelerating expansion of the universe, but in any particular galaxy they are exceedingly rare, so by monitoring large areas of the sky (ideally, the entire sky), we can discover supernovae frequently.

The mass distribution of our universe subtly affects the alignment and shapes of distant galaxies through a phenomenon known as weak gravitational lensing. Understanding these distortions and correlations requires a statistical approach looking at many galaxies across large swaths of sky.

Closer to home, small galaxies that have come too close our Milky Way galaxy are pulled apart into stellar streams that require a “big picture” approach to discover and map. The dark matter distribution in our Milky Way galaxy plays an important role in shaping these stellar streams—our galaxy contains about ten times as much dark matter as normal matter.

With wide-field surveys, not only do we need to cover large areas of sky, but we also want to be able to see the faintest and most distant objects. That latter property is referred to as “going deeper”.

The LSST will provide a dramatic increase in light gathering power over previous survey instruments. The total number of photons collected by a survey instrument per unit time is known as the étendue, a French word, and it is the field of view (in square degrees) × the effective aperture (in m²) × the quantum efficiency (unitless fraction). The units of étendue are thus m²deg². Note that the vertical axis in the graph below is logarithmic, so the LSST will have a significantly higher étendue than previous survey instruments.

The largest monolithic mirrors in the world are fabricated at the Steward Observatory Mirror Lab at the University of Arizona in Tucson. The largest mirrors that can be produced there are 8.4 meters, and LSST has one of them.

Remember the Yerkes Observatory 40-inch refractor, completed in 1897? It has held the record as the largest lens ever used in an astronomical telescope. Until now. A 61.8-inch lens (L-1) and a 47.2-inch (L-2) have been fabricated for use in the LSST camera.

L-1, the largest lens ever produced, is the front lens of the LSST camera

LSST will utilize a camera that is about the size of a car. It is the largest camera ever built for astronomy.

The LSST camera will produce 3.2 gigapixel images. You would need to cover about half a basketball court with 4K TV screens to display the image at full resolution.

An image will be produced every 15 seconds throughout the night, every clear night, and each patch of sky will be reimaged every three nights. That is a HUGE amount of data! ~10 Tb of data each night. Fiber optical cable will transport the data from Cerro Pachón to the National Center for Supercomputing Applications in Urbana, Illinois, where it will be prepared for immediate use and made publicly available to any interested researcher. The amount of data is so large that no one will be downloading raw data to their local computer. They will instead be logging in to the supercomputer and all processing of the data will be done there, using open source software packages.

There are many data processing challenges with LSST data needing to be solved. Airplane, satellite, and meteor trails will need to be carefully removed. Many images will be so densely packed with overlapping objects that special care will be needed separating the various objects.

One LSST slide that Keith presented showed “Solar System Objects: ~ 6 million” and that piqued my interest, given my ongoing research program of observing stellar occultations by asteroids and trans-Neptunian objects for IOTA. Currently, if you endeavor to observe the highest probability occultation events from a fixed observatory location each night, you will be lucky to record one positive event for every ten negative events (no occultation). The reason for this is that our knowledge of the orbital elements of the small bodies of the solar system is not yet precise enough to accurately predict where stellar occultation events will occur. Gaia DR3, scheduled for the latter half of 2021, should significantly improve the precision of small body orbits, and even though LSST does not have nearly the astrometric precision of Gaia, it will provide many valuable astrometric data points over time that can be used to refine orbital elements. Moreover, it is expected that LSST will discover—with its much larger aperture than Gaia—at least 10 times the number of asteroids and trans-Neptunian objects that are currently known.

During the question and answer period after the lecture, I asked Keith what effect the gigantic increase in the number of satellites in Earth orbit will have on LSST operations (global broadband internet services provided by organizations like SpaceX with its Starlink constellation). He stated that this definitely presents a data processing challenge that they are still working on.

An earlier version of Keith’s presentation can be found here. All images in this article except the first (OED) come from Keith’s presentation and have not been altered in any way.

References

Bechtol, Keith, “The Big Picture: Science with Astronomical Surveys” (lecture, University of Wisconsin Space Place, Madison, November 12, 2019).

Bechtol, Ellen & Keith, “The Big Picture: Science and Public Outreach with Astronomical Surveys” (lecture, Wednesday Night at the Lab, University of Wisconsin, Madison, April 17, 2019; University Place, Corporation for Public Broadcasting, PBS Wisconsin).

Jones, R. L., Jurić, M., & Ivezić, Ž. 2016, in IAU Symposium, Vol. 318, Asteroids: New Observations, New Models, ed. S. R. Chesley, A. Morbidelli, R. Jedicke, & D. Farnocchia, 282–292. https://arxiv.org/abs/1511.03199 .

Oxford English Dictionary Online, accessed November 17, 2019, https://www.oed.com/ .

Why Are We Here?

George F. R. Ellis writes in Issues in the Philosophy of Cosmology:

9.1.6 The metaphysical options
…there appear to be basically six approaches to the issue of ultimate causation: namely Random Chance, Necessity, High Probability, Universality, Cosmological Natural Selection, and Design. We briefly consider these in turn.
Option 1: Random Chance, signifying nothing. The initial conditions in the Universe just happened, and led to things being the way they are now, by pure chance. Probability does not apply. There is no further level of explanation that applies; searching for ‘ultimate causes’ has no meaning.
This is certainly logically possible, but not satisfying as an explanation, as we obtain no unification of ideas or predictive power from this approach. Nevertheless some implicitly or explicitly hold this view.
Option 2: Necessity. Things have to be the way they are; there is no other option. The features we see and the laws underlying them are demanded by the unity of the Universe: coherence and consistency require that things must be the way they are; the apparent alternatives are illusory. Only one kind of physics is self-consistent: all logically possible universes must obey the same physics.
To really prove this would be a very powerful argument, potentially leading to a self-consistent and complete scientific view. But we can imagine alternative universes! —why are they excluded? Furthermore we run here into the problem that we have not succeeded in devising a fully self-consistent view of physics: neither the foundations of quantum physics nor of mathematics are on a really solid consistent basis. Until these issues are resolved, this line cannot be pursued to a successful conclusion.
Option 3: High probability. Although the structure of the Universe appears very improbable, for physical reasons it is in fact highly probable.
These arguments are only partially successful, even in their own terms. They run into problems if we consider the full set of possibilities: discussions proposing this kind of view actually implicitly or explicitly restrict the considered possibilities a priori, for otherwise it is not very likely the Universe will be as we see it. Besides, we do not have a proper measure to apply to the set of initial conditions, enabling us to assess these probabilities. Furthermore, application of probability arguments to the Universe itself is dubious, because the Universe is unique. Despite these problems, this approach has considerable support in the scientific community, for example it underlies the chaotic inflationary proposal. It attains its greatest power in the context of the assumption of universality:
Option 4: Universality. This is the stand that “All that is possible, happens”: an ensemble of universes or of disjoint expanding universe domains is realized in reality, in which all possibilities occur. In its full version, the anthropic principle is realized in both its strong form (if all that is possible happens, then life must happen) and its weak form (life will only occur in some of the possibilities that are realized; these are picked out from the others by the WAP, viewed as a selection principle). There are four ways this has been pursued.
1: Spatial variation. The variety of expanding universe domains is realised in space through random initial conditions, as in chaotic inflation. While this provides a legitimate framework for application of probability, from the viewpoint of ultimate explanation it does not really succeed, for there is still then one unique Universe whose (random) initial conditions need explanation. Initial conditions might be globally statistically homogeneous, but also there could be global gradients in some physical quantities so that the Universe is not statistically homogeneous; and these conditions might be restricted to some domain that does not allow life. It is a partial implementation of the ensemble idea; insofar as it works, it is really a variant of the “high probability” idea mentioned above. If it was the more or less unique outcome of proven physics, then that would provide a good justification; but the physics underlying such proposals is not even uniquely defined, much less tested. Simply claiming a particular scalar field with some specific stated potential exists does not prove that it exists!
2: Time variation. The variety of expanding universe domains could be realised across time, in a universe that has many expansion phases (a Phoenix universe), whether this occurs globally or locally. Much the same comments apply as in the previous case.
3: Quantum Mechanical. It could occur through the existence of the Everett-Wheeler “many worlds” of quantum cosmology, where all possibilities occur through quantum branching. This is one of the few genuine alternatives proposed to the Copenhagen interpretation of quantum mechanics, which leads to the necessity of an observer, and so potentially to the Strong Anthropic interpretation considered above. The many-worlds proposal is controversial: it occurs in a variety of competing formulations, none of which has attained universal acceptance. The proposal does not provide a causal explanation for the particular events that actually occur: if we hold to it, we then have to still explain the properties of the particular history we observe (for example, why does our macroscopic universe have high symmetries when almost all the branchings will not?). And above all it is apparently untestable: there is no way to experimentally prove the existence of all those other branching universes, precisely because the theory gives the same observable predictions as the standard theory.
4: Completely disconnected. They could occur as completely disconnected universes: there really is an ensemble of universes in which all possibilities occur, without any connection with each other. A problem that arises then is, What determines what is possible? For example, what about the laws of logic themselves? Are they inviolable in considering all possibilities? We cannot answer, for we have no access to this multitude of postulated worlds. We explore this further below.
In all these cases, major problems arise in relating this view to testability and so we have to query the meaningfulness of the proposals as scientific explanations. They all contradict Ockham’s razor: we “solve” one issue at the expense of envisaging an enormously more complex existential reality. Furthermore, they do not solve the ultimate question: Why does this ensemble of universes exist? One might suggest that ultimate explanation of such a reality is even more problematic than in the case of single universe. Nevertheless this approach has an internal logic of its own which some find compelling.
Option 5: Cosmological Natural Selection. If a process of re-expansion after collapse to a black hole were properly established, it opens the way to the concept not merely of evolution of the Universe in the sense that its structure and contents develop in time, but in the sense that the Darwinian selection of expanding universe regions could take place, as proposed by Smolin. The idea is that there could be collapse to black holes followed by re-expansion, but with an alteration of the constants of physics through each transition, so that each time there is an expansion phase, the action of physics is a bit different. The crucial point then is that some values of the constants will lead to production of more black holes, while some will result in less. This allows for evolutionary selection favouring the expanding universe regions that produce more black holes (because of the favourable values of physical constants operative in those regions), for they will have more “daughter” expanding universe regions. Thus one can envisage natural selection favouring those physical constants that produce the maximum number of black holes.
The problem here is twofold. First, the supposed ‘bounce’ mechanism has never been fully explicated. Second, it is not clear—assuming this proposed process can be explicated in detail—that the physics which maximizes black hole production is necessarily also the physics that favours the existence of life. If this argument could be made water-tight, this would become probably the most powerful of the multiverse proposals.
Option 6: Purpose or Design. The symmetries and delicate balances we observe require an extraordinary coherence of conditions and cooperation of causes and effects, suggesting that in some sense they have been purposefully designed. That is, they give evidence of intention, both in the setting of the laws of physics and in the choice of boundary conditions for the Universe. This is the sort of view that underlies Judaeo-Christian theology. Unlike all the others, it introduces an element of meaning, of signifying something. In all the other options, life exists by accident; as a chance by-product of processes blindly at work.
The prime disadvantage of this view, from the scientific viewpoint, is its lack of testable scientific consequences (“Because God exists, I predict that the density of matter in the Universe should be x and the fine structure constant should be y”). This is one of the reasons scientists generally try to avoid this approach. There will be some who will reject this possibility out of hand, as meaningless or as unworthy of consideration. However it is certainly logically possible. The modern version, consistent with all the scientific discussion preceding, would see some kind of purpose underlying the existence and specific nature of the laws of physics and the boundary conditions for the Universe, in such a way that life (and eventually humanity) would then come into existence through the operation of those laws, then leading to the development of specific classes of animals through the process of evolution as evidenced in the historical record. Given an acceptance of evolutionary development, it is precisely in the choice and implementation of particular physical laws and initial conditions, allowing such development, that the profound creative activity takes place; and this is where one might conceive of design taking place. [This is not the same as the view proposed by the ‘Intelligent Design’ movement. It does not propose that God tweaks the outcome of evolutionary processes.]
However from the viewpoint of the physical sciences per se, there is no reason to accept this argument. Indeed from this viewpoint there is really no difference between design and chance, for they have not been shown to lead to different physical predictions.

A few comments.

1: Random chance. At first, this strikes one as intellectual laziness, but perhaps it is more a reflection of our own intellectual weakness. More on that in a moment.

2: Necessity. Our intellectual journey of discovery and greater understanding must continue, and it may eventually lead us to this conclusion. But not now.

3: High probability. How can we talk about probability when n = 1?

4: Universality. We can hypothesize the existence of other universes, yes, but if we have no way to observe or interact with them, how can we call this endeavor science? Furthermore, explaining the existence of multiple universes seems even more problematic that explaining the existence of a single universe—ours.

5: Cosmological Natural Selection. We do not know that black holes can create other universes, or that universes that contain life are more likely to have laws of physics that allow an abundance of black holes

First image of a black hole by the Event Horizon Telescope. The object M87* is located at the heart of galaxy Messier 87, about 54 million light years distant. The mass of this supermassive black hole is estimated at 6.5 billion solar masses.

6. Purpose of Design. The presupposition of design is not evidence of design. It is possible that scientific evidence of a creator or designer might be found in nature—such as an encoded message evincing purposeful intelligence in DNA or the cosmic microwave background—but to date no such evidence has been found. Even if evidence of a creator is forthcoming, how do we explain the existence of the creator?

I would now like to suggest a seventh option (possibly a variant of Ellis’s Option 1 Random Chance or Option 2 Necessity).

7. Indeterminate Due to Insufficient Intelligence. It is at least possible that there are aspects of reality and our origins that may be beyond what humans are currently capable of understanding. For some understanding of how this might be possible, we need look no further than the primates we are most closely related to, and other mammals. Is a chimpanzee self-aware? Can non-humans experience puzzlement? Are animals aware of their own mortality? Even if the answer to all these questions is “yes”¹, there are clearly many things humans can do that no other animal is capable of. Why stop at humans? Isn’t it reasonable to assume that there is much that humans are cognitively incapable of?

Why do we humans develop remarkable technologies and yet fail dismally to eradicate poverty, war, and other violence? Why does the world have so many religions if they are not all imperfect and very human attempts to imbue our lives with meaning?

What is consciousness? Will we ever understand it? Can we extrapolate from our current intellectual capabilities to a complete understanding of our origins and the origins of the universe, or is something more needed that we currently cannot even envision?

“Sometimes attaining the deepest familiarity with a question is our best substitute for actually having the answer.” —Brian Greene, The Elegant Universe

“To ask what happens before the Big Bang is a bit like asking what happens on the surface of the earth one mile north of the North Pole. It’s a meaningless question.” —Stephen Hawking, Interview with Timothy Ferris, Pasadena, 1985

¹ For more on the topic of the emotional and cognitive similarities between animals and humans, see “Mama’s Last Hug: Animal Emotions and What They Tell Us about Ourselves” by primatologist Frans de Waal, W. W. Norton & Company (2019). https://www.amazon.com/dp/B07DP6MM92 .

References
G.F.R. Ellis, Issues in the Philosophy of Cosmology, Philosophy of Physics (Handbook of the Philosophy of Science), Ed. J. Butterfield and J. Earman (Elsevier, 2006), 1183-1285.
[http://arxiv.org/abs/astro-ph/0602280]