Why quantize gravity?

When I first read DNLee’s story, I mistakenly thought “ofek” is a four letter word, an internet slang for oh-what-the-fucken-heck. Ofek, then, is all I have to say about my recent grant proposals being declined, one after the other. Ah, scrape the word “recent” – the Swedish Research Council hasn’t funded any one of my project proposals since I moved to Sweden in 2009. So all I can do is to continue to write papers as what feels like the only person working on quantum gravity in Northern Europe. Most painfully, I have had to turn away many a skilled and enthusiastic student wanting to work on quantum gravity phenomenology.

To add insult to injury, the Swedish Research Council publicly lists the titles of the winning proposals. You win if your research contains either “nano” or “neuro”, promises a cure for cancer, green energy, or a combination of the above. The strategy is designed for a bad return on investment. Money goes where lots of people poke the always same questions. If many flies circle the same spot there must be shit to find, the thinking is, let’s throw money at it. Our condensed matter people have no funding issues.

As nations face economic distress and support for basic research dwindles, why would anybody want to work on quantum gravity. Srsly. This question keeps coming back to me; its recurrence time conspicuously coincides with the funding agencies’ call cycles. It factors into my reflection index that women, I read, are drawn to occupations that help others, also occupations where they can use their allegedly superior social and language skills. What’ wrong with me? Why quantize gravity if I could cure cancer instead? Or at least write proposals promising I will, superior languages skills and all.

Modern medicine wouldn’t exist without the technologies that have become possible by breakthroughs in physics. There wouldn’t be any nano or neuro without imaging and manipulating quantum things and without understanding atoms and nucleons. Without basic research in physics, there wouldn’t be CT scans, there wouldn’t be NMR, nuclear power, digital cameras, and there wouldn’t be optical fibers for endovenous laser treatment.

At this point in history we still build on the new ground discovered by physicists a century ago. But the only way we can continue improving our circumstances of living is to increase our understanding of the fundamental laws of nature. And at the very top of the list there’s the question what is space and time, and how can we manipulate quantum objects. In my mind, these questions are intimately related. In my mind, that’s the ground the technologies of the next centuries will be built upon. In my mind, that’s how my occupation contributes to society – not to this generation maybe, but to the coming ones. Quantum gravity, quantum information, and the foundations of quantum mechanics are what will keep medicine advancing when nano and neuro has peaked and busted. Which will happen, inevitably, sooner or later.

So why quantum gravity? Because we know our knowledge of nature is incomplete. There must be more to find than we have found so far.

The search for quantum gravity is often portrayed as a search for unification. All other interactions besides gravity are quantized, there’s no unifying framework and that’s what physicists are looking for. It’s an argument from aesthetics, and it’s an argument I don’t like. Yes, it is unaesthetic to have gravity stand apart, but the reason we look for a quantum theory of gravity is much stronger than that: We know that unquantized gravity is incomplete and it is inconsistent with quantum theory. It isn’t only that we don’t know how to quantize gravity and that bugs us, we actually know that the combination of theories we presently have does not describe space and time at the fundamental level.

The strongest evidence for this inconsistency are the occurrence of singularities in unquantized gravity and the black hole information problem. The singularities are a sign that the unquantized theory breaks down and is incomplete. The black hole information problem shows that combining unquantized gravity with quantized matter is inconsistent – the result of combining them is incompatible with quantum theory.

Most importantly, we know that quantum particles can exist in superposition states, they can be neither here nor there. We also know that all particles carry energy and all energy creates a gravitational field. We thus know that the gravitational field of a superposition must exist, but we don’t know what it is. If the electron goes through both the left and the right slit, what happens to its gravitational field? Infuriatingly, nobody knows.

Nobody knows isn’t to say that nobody has an answer. Everybody seems to have an answer, the flies are circling happily. So I’ve made it my job to find out how we can ever know, which leads me to the question how to experimentally test quantum gravity. Without finding observational evidence, quantum gravity should be taught in the math or philosophy departments, not in the physics departments.

The irony is that quantum gravity phenomenology is as safe an investment as it gets in science. We know the theory must exist. We know that the only way it can be scientific is to make contact to observation. Quantum gravity phenomenology will become reality as surely as volcanic ash will drift over Central Europe again.

Every time I go down this road of self-doubts, I come out at the same place, which is right here in my office with my notepad and the books and the piles of papers. Quantum gravity is the next level of fundamental laws. The theory has to be connected to experiment. Quantum gravity is my contribution to the future of our societies and to help advance life on planet Earth. And, so I hope, space exploration, eventually. Because I really want ask those aliens a few things.

Today I talked to a professional photographer. Between the apertures and external flash settings and my attempt to produce a smile, I learned that he too has to write proposals for project funding. In his case, that’s portraits taken by a method which, I gather, isn’t presently widely used and not very popular with the Swedes. It’s neither nano nor neuro and it wasn’t funded.

Money is time, and time flies, and so in the end the most annoying part is all the waste of time that I could have used better than searching for pretty adjectives to decorate my proposals. Your tax money at work. Neuro-gravity anybody? Nano is also a four-letter word.