Ask Ethan: Why do scientists avoid the possibility of God?

Here in our Universe, the main goal of the scientific endeavor is to make as much sense of all of the phenomena that we can perceive, observe, and measure in some way. We strive to not only describe the nature of reality as comprehensively and accurately as possible, but also to come up with models of reality that enable us to make accurate predictions about what we’re likely to observe given any arbitrary set of initial conditions. In the best-case scenario, we can concoct a fully-formed, logically consistent physical theory that describes our reality, and it will have an enormous range of validity, enabling us to make predictions even about hitherto unforeseen phenomena.

This method has been tremendously successful for science, as we’ve discovered what makes up the Universe, in what proportion, and what the force laws are that govern physical scales ranging from the subatomic to the cosmological. We look to the Universe itself, posing questions to nature directly via scientific experiments, measurements, and observations, in our attempts to reveal what governs reality, including to determine our ultimate origins and our ultimate fate. But, by restricting ourselves to the physical, are we leaving out the very real possibility of the supernatural? That’s what Barry Fetzer wants to know, following up on this recent article to ask:

“If our imaginations are, in fact, limitless, then God has to be considered as a reason for our existence. As wild as some of your other listed theories are (a la Twilight Zone’s extra dimensions?), shouldn’t intelligent design be listed too? Why is it that some scientists who should be open to all possibilities often refuse to even permit the possibility of intelligent design?”

I’m lifting the temporary restraining order between science and religion to consider this question as fairly and honestly as possible. Science, after all, can’t rule out the supernatural. So how should a scientist responsibly think about these big, existential questions? Let’s dive in.

This is the first image of Sgr A*, the supermassive black hole at the center of our galaxy. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. Its measured mass of 4.3 million solar masses places it among the smallest supermassive black holes of all, and it possesses an entropy of ~10^91 k_B, or about 1000 times as much entropy as was contained in the observable Universe some 13.8 billion years ago.

The first place we need to begin is with the very process by which we gather information about the Universe: what scientists refer to as an underlying data set. Everything that we observe or measure in existence is, potentially, a data point that can contribute to such a data set. We learn about the Universe, at a fundamental level, by gathering the information that it reveals to us about itself through:

• experiment,
• measurement,
• and observation.

Despite our love of theories, ideas, and hypotheses in science, the scientific endeavor, at its core, is about confronting those ideas with the realities of nature itself. From astronomy to physics to chemistry to biology to geology to medicine to psychology and the social sciences, the data that we gather is the best window into the actual reality of nature that we have.

That’s why scientists — even theorists, like me — so often make appeals to the importance of experiment, and of putting the question of “what is reality like” to our physical reality itself to the Universe itself. The way we learn about reality isn’t by thinking about reality; it’s about measuring what’s real, and using that measured reality to inform, test, validate, and refute our various ideas surrounding how reality could be. Our imaginations, our theories, and our mathematical predictions can take us to all sorts of places for how reality could be, but it’s our observations and measurements of reality that allow us to pick out how reality actually is.

As shown in an episode of Mythbusters, a projectile fired backward from a forward-moving vehicle at the exact same speed will appear to fall directly down at rest; the velocity of the truck and the exit velocity from the ‘cannon’ exactly cancel each other out in this take. If you calculate, from the moment the ball is released, when it should hit the ground, you actually get two answers: a positive time and a negative time solution. Only physics can tell you which one (the positive solution) corresponds to reality.

Next, we’re ready to move on to the ways we make sense of that data, again, from a scientific perspective. A lot of people mistakenly think that the goal of a scientific theory is to describe what actually happens in nature, and in particular, to tell you what end-state phenomena are going to arise from a given set of initial conditions. Science, and scientific theories, can indeed accomplish that task for you under certain circumstances, but that’s not a comprehensive description of what the goal of a scientific theory is. In fact, predicting the end-state of a system is only a very small part of what science does as far as making sense of reality goes.

When it comes to the goals of science, what we hope for can be described in stages. The lowest-level stage is to make a model of some aspect of reality that’s useful for describing that aspect of reality, and for making a model that succeeds where other such models fail. One such example from ancient history concerns the nature of wind. Thousands of years ago, many thought that wind was fundamental, and that it required some other impetus to generate it, like the oceans, a volcanic vent, or humans blowing air out of their mouths. Others, meanwhile, thought that air existed even in the absence of wind, and that this air took up space and could even exert a force, all on its own.

How would we decide which scientific model better reflected reality?

This map shows a short period of wind data across the continental United States. While many once thought of wind as a phenomenon that required a source and was its own fundamental element, others held that wind was just a manifestation of air in motion, and that even air itself took up space and was capable of exerting forces. That latter viewpoint was a minority one, until the pre-Socratic philosopher/scientist Empedocles demonstrated the answer.

The answer turned out to be experimental, and was provided by the Ancient Greek scientist Empedocles. Empedocles, although he’s perhaps most well known for his natural philosophy, instead conducted an experiment using a hollowed-out gourd. Gourds, back in Empedocles’s day, were often used for carrying water. You’d hollow it out, poke holes in the bottom, and cut a hole in the top that you could place your finger over. This device, known as a water-thief (or clepsydra), was used to:

• gather water by submerging the gourd,
• carrying water by placing your finger over the top and lifting the filled gourd out and carrying it,
• and then using it as a water-pouring device (like a watering can or for distribution into drinking vessels) by removing your finger and letting the water fall out of the bottom.

This is actually incredible. If you plunge the gourd into a stream, lake or river, and it fills with water. If you lift the gourd up, the water leaks out of the bottom. But place your thumb or hand over the top, and the water immediately stops flowing out of the bottom.

Why? What is happening?

There must be something pushing back up on the water, right at the holes at the bottom, to prevent it from falling down. But there’s nothing there at all when there’s no wind, so what could it be? This is how we make sense of the world: it must be air, down there, taking up space and exerting a force. Even though we can’t see it, we know it must be there because we observe its effects. That’s how Empedocles proved that air takes up space, can exert a force, and exists even in the absence of wind.

This collection of hollowed-out gourds serve as water vessels. In antiquity, hollow gourds would have holes poked in the bottom and an opening at the top, so one could immerse and fill these jugs with water, then put your thumb over the top hole and carry the water back until you were ready to let it out again.

The model of “air exists without wind, and wind is just moving air” is a good scientific model, and in fact a better scientific model than the alternative, because it sufficiently explains a phenomenon that the alternative model cannot. Even without wind, air pushes up on the water at the bottom of the holes in the bottle.

Empedocles didn’t know everything there was to know about nature, of course. He didn’t know that air wasn’t fundamental, but rather was made up of small component particles — molecules — that exerted a pressure (a force over an area) that was dependent on properties like density and temperature. He didn’t know that the reason the water doesn’t fall down when your finger is over the top of the water-thief is because it would create a vacuum inside the water-containing device if it did: forbidden by the rules governing forces and pressure for materials of this density. And he didn’t know that when you remove your finger from the top, the water falls down because air is flowing into the top of gourd, allowing the water to simultaneously flow out of the bottom.

There was plenty more to learn, because what Empedocles had done was just the beginning of science: to propose a model that was more successful than the other models of his time, as verified through observation, measurement, and experiment.

If you poke holes in the bottom of a filled water bottle, water will leak out of the bottom if the top is not covered in an airtight fashion. If the top is covered in an airtight way, water cannot leak out, proving that air exerts a force. However, if air can rush in through the top, water is free to fall through the holes on the bottom here on Earth.

In a very real way, this illustrates the process of science. We can often advance from the start line by putting forth a simple idea or hypothesis that explains one phenomenon better than all the other competing ideas, and test-and-verify that it does so experimentally as often or as thoroughly as we like. But we don’t stop there; we can then improve upon that idea by trying to make a grander, overarching framework that contains or encapsulates that idea or hypothesis with more explanatory power, more predictive power, and a wider range of validity. A good illustration of this comes by considering the science of modern cosmology: the field of science that just happens to contain our best theories of the origin of the Universe.

Although people had been attempting to make sense of the Universe since antiquity, their best models were only descriptive, not prescriptive. They didn’t tell you how things were happening; they only helped tell you what would happen. Planetary motion was thought of in terms of orbits, like Ptolemy, Aristarchus, or even Copernicus, and assumptive prejudices (in favor of circles) ran amok, unchecked. It was Kepler who first overcame that, coming up with his laws of planetary motion to explain the orbits of the planets in a superior, more accurate fashion than all of his predecessors. If we had discovered Uranus and Neptune back in Kepler’s day, his laws could have predicted their orbits, too, but even Kepler didn’t link planetary motion to gravitation, and to the accelerations experienced by falling objects here on Earth.

Even before we understood how the law of gravity worked, we were able to establish that any object in orbit around another obeyed Kepler’s second law: it traced out equal areas in equal amounts of time, indicating that it must move more slowly when it’s farther away and more quickly when it’s closer. At every point in a planet’s orbit, Kepler’s laws dictate at what speed that planet must move. The force law that describes Keplerian orbits was not discovered until generations later, when Newton accomplished the feat.

That would fall to Newton, whose law of universal gravitation vastly extended the range of validity of our scientific theory that attempted to make sense of the Universe. Planets were spherical because of their self-gravitation. Objects fell downward on Earth because of the same force of gravity that kept the Moon in orbit around Earth. The moons of Jupiter and the rings of Saturn orbited their parent planets because of the same law of gravity that kept the planets in orbit around the Sun. And other stars would exert their own gravitational forces, implying that they could have their own rich stellar and planetary systems as well.

It would take centuries before we ran up against the limits of Newton’s theories, with the orbit of Mercury failing to match Newton’s (and Kepler’s) predictions by slight but significant amounts. Meanwhile, objects moving close to the speed of light didn’t obey the laws of classical mechanics: Newton’s laws of motion. Maxwell’s theory of electromagnetism indicated a maximum speed for the propagation of any signal — the speed of light in a vacuum — and yet Newton’s gravitation demanded that gravity propagate at infinite speeds.

It would take several advances, strokes of genius, and strenuous tests of verification to make the critical sets of advances, but when the dust settled, we had a new theory of gravity: Einstein’s General Relativity.

An animated look at how spacetime responds as a mass moves through it helps showcase exactly how, qualitatively, it isn’t merely a sheet of fabric. Instead, all of 3D space itself gets curved by the presence and properties of the matter and energy within the Universe. Space doesn’t “change shape” instantaneously, everywhere, but is rather limited by the speed at which gravity can propagate through it: at the speed of light. The theory of general relativity is relativistically invariant, as are quantum field theories, which means that even though different observers don’t agree on what they measure, all of their measurements are consistent when transformed correctly.

Over the course of the 20th and 21st centuries, we’ve developed our picture of reality even further. Matter isn’t just made of atoms and molecules, but of fundamental subatomic quanta that combine together to create every form of matter we find on Earth. Gravitation and electromagnetism are just two of the fundamental forces in the Universe, joined by the strong and weak nuclear forces. There are more particles than the ones that compose atoms (up and down quarks, gluons, and electrons) and light (photons), but a whole Standard Model “zoo” of elementary particles. And our Universe wasn’t static and eternal, as had long been assumed, but was expanding and cooling, implying that it was hotter, denser, and smaller in the past.

As the evidence rolled in supporting our picture of the hot Big Bang, and then subsequently, an extension to that theory known as cosmic inflation, we recognized that our Universe didn’t begin from a singularity that birthed space and time some 13.8 billion years ago. Instead, the hot Big Bang was set up and preceded by an earlier phase of rapidly and relentlessly expanding empty space, with quantum fluctuations stretched across that space to seed our Universe with imperfections that would later grow into the grand cosmic web we now observe today. When we turn back the clock as far as we know how to do it, this is the earliest known epoch in time that’s supported by observable scientific evidence.

The quantum fluctuations inherent to space, stretched across the Universe during cosmic inflation, gave rise to the density fluctuations imprinted in the cosmic microwave background, which in turn gave rise to the stars, galaxies, and other large-scale structures in the Universe today. This is the best picture we have of how the entire Universe behaves, where inflation precedes and sets up the Big Bang. Unfortunately, we can only access the information contained inside our cosmic horizon, which is all part of the same fraction of one region where inflation ended some 13.8 billion years ago.

So then, what about the question of God, or the supernatural? Throughout history, many thinkers — scientists and non-scientists alike — have looked at what science didn’t currently know, wherever there was a gap in our explanatory and/or predictive power, or beyond the current limits of the established range of validity of our known theories, and have asked exactly that: how do you know there isn’t some sort of divine intervention that occurred here?

• How do you know that life on Earth arose naturally from non-life, and that there wasn’t a “divine spark” that started it off?
• How do you know that humans arose through purely evolutionary processes, and that there wasn’t a divine hand guiding evolution towards our existences?
• How do you know that there isn’t a soul within the body: something that goes beyond our material Universe?
• And, for that matter, how do you know that the Universe really is 13.8 billion years old and began with a hot Big Bang, and wasn’t designed and created as is some ~6000 years ago, with the geological and fossil records already existing within Earth, in a human-centric fashion?

The truth is that we don’t “know” these things the way you can mathematically or logically prove a fact; we don’t. What we do is we look for any gaps or holes or inconsistencies in our scientific explanations for what we observe and measure. If we don’t find them, there’s no need or reason to “insert” something extraneous or unnecessary, and so we don’t. If we do find gaps or holes or inconsistencies, we investigate them scientifically, looking for a physical mechanism, one rooted in our measurable reality, to attempt to explain them.

The Universe as we observe it today began with the hot Big Bang: an early hot, dense, uniform, expanding state with specific initial conditions. But if we want to understand where the Big Bang comes from, we must not assume it’s the absolute beginning, and we must not assume that anything we can’t predict doesn’t have a mechanism to explain it.

That’s where we are at the current frontiers of science, including of the science of the origin of our Universe. When we confront something that we can’t explain, we propose new testable, falsifiable hypothesis that, ideally, lead to three things.

1. Can you still explain all of the pre-existing successes of the prior theory with your new one? (In other words, does what we already know rule out your new idea, rendering it dead-on-arrival?)
2. Does the new idea succeed where the prevailing theory fails? (In other words, does it successfully explain the “gap” in our knowledge or explanations or predictions?)
3. And does it make novel, testable predictions that differ from the prevailing theory’s predictions, so that we can (at least in principle) go out and test them?

That’s what we look for, at least, from a scientific point of view.

That’s why we don’t just say “things must have been born like this” or “it was probably God-given” or “it involves divine intervention.” It isn’t that those explanations are impossible; it’s that they aren’t testable scientifically. Science — and you might not agree, but I’m going to say it anyway — is the only way we’ve ever advanced human knowledge in all of human history, and to resort to unscientific or non-scientific reasoning is to basically give up on finding out the answers about reality for ourselves. It isn’t that it’s impossible for there to be a divine presence in our Universe, but rather that if it existed and if it affected our reality in a measurable, observable fashion, science would reveal it, and we wouldn’t think of it as “divine” any longer.

The truth is we do admit God’s existence as a possibility; it just doesn’t count as a scientific explanation. If “God” does turn out to be the answer to one or more of the questions that we have about our Universe, science will never be able to reveal it. And that’s okay; all knowledge is fundamentally limited, even if our imaginations aren’t. Those of us who practice science just aren’t ready to give up on the possibility that, just possibly, our current scientific questions do have answers that can be uncovered through interrogating reality by whatever means our imaginations can concoct.

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