“There could be no fairer destiny for any physical theory than that it should point the way to a more comprehensive theory in which it lives on as a limiting case.” –Albert Einstein
Imagine: you’ve worked hard all your life, through your primary and secondary school education, where you worked hard to get into a good college, through your undergraduate degree, where you found something you were passionate enough about that you wanted to study it even further, and then through graduate school, where you spent half-a-decade or more immersing yourself, non-stop, in an area of research in a field that you love.
You become familiar with the deepest known theories about whatever it is you’ve studied, and you begin to see where our understanding in some part of the material world begins to break down. The great unsolved problems of your time look like missing puzzle pieces, while the tools, equations and current theories begin to look like misshapen pieces that don’t quite fit where they’re supposed to.
In other words, you’ve run up against the limits of our current knowledge; to make any further progress is going to take an innovation that’s not yet a part of our scientific lexicon.
Maybe you’re a biologist, trying to understand how the sensation of itch actually works. The three main types of sensory neuron in humans — pain, pressure and temperature — don’t quite seem to cover it.
Maybe you’re a geoscientist, trying to figure out how to predict when the entire mantle convects, and when only the upper mantle convects to transport heat and materials.
Maybe you’re a particle physicist, trying to decipher what accounts for neutrino mass, and why they’re so mind-bogglingly light compared to all the rest of the massive, standard model particles.
Or maybe — like me — you’re an astrophysicist, trying to solve some of the great cosmic mysteries of just how it is our Universe got here, and came to be the way it is today.
The thing is, no matter what your field is, there’s more to learn, there’s progress to be made, and there’s work to be done. If the current theories and laws can’t explain everything that’s observed — all the experimental and observational phenomena — then that theory cannot be the entire story.
And in that sense, given that even the best scientific theory only has a limited range of validity, all scientific theories are wrong. (And before you quote me out-of-context on that, keep reading.)
But that’s not really fair. Scientific theories are only meant to have a certain range of validity! We know that the Big Bang doesn’t explain what came prior to the Big Bang; we know that evolution doesn’t explain the origin of life; we know that Airy’s theory of isostatic compensation doesn’t explain the motion of the Earth’s crust over geologic timescales; we know that General Relativity doesn’t explain the existence of antimatter.
But we want to know the answer to all of those questions. And that requires new ideas; it requires new scientific theories.
To explain what happens prior to the Big Bang, we have the theory of cosmic inflation. To explain the origin of life, we have the theory of abiogenesis. To explain the motion of Earth’s crust, we have plate tectonics. And to explain the existence of antimatter, we have quantum field theory. All of these theories are very likely valid, as far as we understand them, but none are necessarily the final, complete and fully comprehensive answer to these questions.
And moreover, these are just the most successful ones; along the way, there were plethoras of alternative scientific theories that didn’t quite pan out. Here are some of the more interesting ones from my field: astrophysics.
We know that black holes come in a couple of different varieties, ranging from a handful of solar masses (from collapsed supermassive stars) all the way up to millions or billions of times the mass of our Sun: the supermassive black holes found mostly at the center of galaxies. But could the Universe have been filled with lower-mass black holes from the early stages of the Universe? That’s the theory of primordial black holes, or PBHs!
Now these have been of interest for a number of reasons — as a dark matter candidate, for example — for some time. But we’ve looked for them, we’ve investigated their physics, we’ve tested the theory for compatibility with our current knowledge of large-scale structure of the Universe, and it just doesn’t seem to fit with what we know. It’s still a possibility, but a remote-looking one, and it doesn’t solve the problems it was designed to solve. So, no PBHs; that’s a scientific theory that’s wrong (so far), but it’s still interesting to think about.
We know that structure, on the largest scales, forms into giant superclusters with a certain large-scale distribution. Clumps beyond a certain size don’t seem to exist; and the large-scale features we do see tell us what the Universe is (and isn’t) made out of. But one of the great ideas that came along was that large-scale structure could have been seeded by a network of cosmic strings, or giant one-dimensional defects in the fabric of spacetime!
But despite a reasonable theoretical motive behind them, we’ve performed exhaustive surveys of our Universe, and the evidence against cosmic strings is overwhelming. The nail-in-the-coffin that our Universe’s structure doesn’t follow from cosmic strings came with the measurement of the low-multipoles from the COBE satellite; the disagreement is too much. But cosmic strings are still interesting to thing about for a variety of reasons, and could rear their head in the future in some other form.
One of the most important parts of relativity is the idea that experimental results are independent of what direction your experiment is oriented in, and also is independent of what your linear velocity happens to be. This, generally, is known as Lorentz invariance, and is a symmetry that — as far as we know — is always respected by nature.
But if you break this invariance, a whole slew of interesting phenomena could happen. And so we look, and we build theories based on breaking it. So far, the only results are null, within our statistical limits. But that doesn’t mean, at some level, this couldn’t potentially be interesting.
I don’t bring any of these ideas up to try and convince you that they’re right; I don’t think any of them are!
But I bring this up so that the next time you hear about some theory, it’s totally reasonable to ask, “What overwhelming evidence do we have that this is correct?” But rather than simply dismiss it, if it sets off your internal BS-detector, I want to assure you of a number of things:
- Your BS-detector is probably right (and honestly, it’s probably not sensitive enough), and this isn’t likely to be the next great revolution in our understanding of the Universe,
- This research is still important, as it’s exploring a hitherto unexplored possibility, which could teach us something about the Universe,
- and if there’s even a germ of a good idea in there, scientific inquiry is what will grow that into a full-fledged theory that means something.
Most scientists go through their entire career without coming up with even one original idea, and most of the ideas that they do come up with aren’t worth the weight of the paper they’re printed on. But you’ve got to try, or you’ll never move forward. The danger of putting yourself out there and finding out that you might not be right is far worse than not putting yourself out there at all.
It’s a great big Universe out there, and there’s still so much to be understood. I’m one of the least inclined to be credulous about a new idea in my field, but even I recognize why it’s important. Trying new things, learning why they fail, and trying again is the only way progress has ever been made; let’s continue to encourage people to do just that. Be daring, be bold, and dare to be a success. If you fail, it shouldn’t cost you your career; if you succeed, all of humanity wins!