Top 10 scientific mysteries for the 21st century

Solving the toughest problems posed by nature is not just fun and games

Calabi-Yau manifold

Calabi-Yau manifolds like this one represent extra dimensions tightly curled and wound up so they can't be detected. The question of how many dimensions of space there actually are is one of the top scientific mysteries for 21st century scientists to solve.

Rogilbert/Wikimedia Commons

The last few centuries have been pretty good for science. In the 17th century, Isaac Newton solved the ancient controversy over the nature of forces and motion with his three laws. In the 18th, Ben Franklin figured out a lot about electricity. In the 19th, Darwin explained the diversity of species, Maxwell revealed the physics of light, Mendeleyev defined the families of chemical elements. In the 20th we had Einstein, who figured out all sorts of stuff, including gravity. No to mention Watson and Crick, who deciphered the molecular foundation for genetics and life. What more do you want?

Well, there are still lots of mysteries left for the 21st century to solve, and it has only 86 years left in which to solve them. So it’s a good idea to put them in a list, just to avoid any danger that everybody will forget to work on them.

Actually there are many more than 10, so this list will have to be restricted to my favorites. To select from all the many possibilities, let’s make a game of it.

10. How did life originate?

It doesn’t seem like this one should be so hard, but it continues to defy solution. There’s plenty of speculation, often related to RNA’s ability to act both as catalyst and bio–hard drive to store information. And new findings turn up all the time about how life’s basic building blocks could have been generated in primordial conditions or delivered to Earth from space. I think this question will end up having something to do with game theory, as biomolecules interact in competitive ways that could be described as strategies, and the math for calculating optimal strategies is what game theory is all about.

9. What is the identity of the dark matter?

It has been eight decades or so since astronomers began to notice that there is more gravity pulling stuff around out in space than there is visible matter able to produce such effects. Attempts to detect the supposedly exotic (as in, unknown) species of subatomic particle responsible for the extra gravity have been frustrating. Hints seen in some experiments have been ruled out by other experiments. I think there’s a missing piece to this puzzle, but it probably has nothing to do with game theory.

8. What is the nature of the dark energy that drives cosmic acceleration?

If you think dark matter is frustrating, try explaining dark energy. Something is driving space to expand at an ever increasing rate. Physicists think that they know what it is — the never-changing density of energy residing throughout all of space, referred to by Einstein as the “cosmical term” and now called the cosmological constant. But when you calculate how strong the cosmological constant should be, the answer is too big by dozens of orders of magnitude — much more than the difference between the size of the entire universe compared with a proton. So dark energy’s identity remains a mystery; if it is the cosmological constant, something else is seriously wrong with what physicists think they know. And so far game theory has been absolutely no help.

7. How to measure evidence

This one is so mysterious that many scientists don’t even know there’s a mystery. But if they paused to think, they’d realize that the standard way of inferring conclusions from experimental data — calculating “statistical significance” — makes about as much sense as punting on fourth and seven when you’re down by 15 with eight minutes to go. One small example: if you do an experiment and get a statistically significant result, and then repeat it and get a statistically significant result again, you’d think you have better evidence than doing the experiment only once. But if the significance level was a little less the second time, the combined “P value” would be less impressive after the second experiment, even though the evidence ought to be regarded as stronger. It’s a mess. Game theory would surely be able to help somehow, possibly by virtue of its relationship to thermodynamics.

6. Genes, cancer and luck

You might have read recently that most cancer is caused by bad luck, as a study published in Science supposedly concluded. (Actually, the study concluded that the disparity in prevalence of cancer of various types was largely due to luck.) A firestorm of protest followed, essentially based on the belief that such a study must be wrong because it would “send the wrong message” to the public. Proving the illogic of that syllogism should be left as an exercise for the reader. Other responses revealed that experts do not agree on how random mutations (bad luck) compare with heredity (parent’s fault) plus lifestyle (your fault) and environmental exposure to bad things (somebody else’s fault) in causing cancer. Sorting all that out, and in the process solving cancer’s other mysteries, should be a high-priority exercise for 21st century science. And yes, there is a considerable amount of research relating game theory to cancer.

5. Are there extra dimensions of space?

I don’t know why people keep thinking this is a mystery, as I have on several occasions pointed out that there are no extra dimensions. However many there are, they are all absolutely necessary. Posed properly, this question should be how many dimensions of space are there? (For that matter, you could also ask about how many time dimensions there are, but that might overlap with No. 4.) Many physicists believe more dimensions than the ordinary three will be needed for physics to make sense of the universe. (Don’t even ask if they’re talking about bosonic or fermionic dimensions.) A key to understanding this issue is the mathematics of Calabi-Yau manifolds, which can curl up in gazillions of different ways to prevent easy detection of the additional dimensions’ existence. And that makes it really hard to figure out which of the gazillion possibilities would correspond to the universe we inhabit (unless there is some sort of fixed point theorem that would choose one, like a Nash equilibrium in game theory). In any event, anyone attempting to solve this riddle should first read Edwin Abbott’s Flatland, in which the protagonist character, A. Square, demonstrates the existence of an extra dimension and is promptly thrown in jail.

4. The nature of time

So many mysteries, so little time in which to solve them, unless solving this one would reveal some clever tricks to play with time. Many submysteries underlie this one, corresponding to almost all of the 44 definitions of time in the dictionary (and that’s just as a noun). What’s the nature of duration and the flow of time — is it illusory or “real” in some elusive way? What about the direction of time — does it always go forward? Why? Is time travel possible, or can messages at least be sent backward in time? (Forward in time is easy — just print this blog post out and read it a year from now.) Perhaps the biggest mystery is whether all these issues about time are related or are completely separate questions. Of course, it would all be simpler if somehow time could be connected to game theory, which it might be, because game theory can be related to cellular automata, which in turn can be related to time.

3. Quantum gravity

Quantum physics and general relativity (aka Einstein’s theory of gravity) both seem to describe the universe and its components with compelling accuracy, yet they seem wholly incompatible with one another. Attempts to combine them into a coherent unified theory have been as successful as brokering compromise in the U.S. Congress. Yet there are clues. In 1930, Einstein tried to refute quantum mechanics (specifically, the Heisenberg uncertainty principle) by suggesting a clock attached to a box hanging on a scale could measure both the mass of a photon and the precise time that it escaped from the box. (Heisenberg said you couldn’t measure both at the same time). But Niels Bohr pointed out that the time on the clock would be uncertain, because as the box moved upward in the gravitational field, Einstein’s relativity required a change in time that would introduce just the amount of uncertainty in the timing that Heisenberg required. So how, you might ask, did the uncertainty principle know about this effect of general relativity? Maybe if the experts posed the question that way they would be able to figure out the quantum gravity mystery. The next best bet would be to undertake the study of quantum game theory, which hasn’t been adequately exploited yet in this regard.   

2. Does intelligent life exist elsewhere?

It’s tempting to delete the “elsewhere,” but given what passes for intelligence on Earth, it makes sense to wonder if anything like it could be blundering about on some distant world. It seems likely, given how many other worlds there are out there. But finding out for sure will probably require receiving an actual message. Projects like SETI have been listening for some such message, so far unsuccessfully. There are two (at least) possible explanations: One, there have been no messages (perhaps the aliens are experts at game theory and calculated that contacting humans would be a bad strategy). Two, the messages are there, but nobody knows how to detect or recognize them. Perhaps enhanced scrutiny is in order on Twitter, where numerous tweets every day seem most plausibly to be the work of aliens. 

1. The meaning of quantum entanglement

All sorts of quantum mysteries remain unsatisfactorily resolved, but maybe the rest would succumb if entanglement does. Entanglement occurs in systems with widely separated parts that share a common history; a measurement of one of the parts reveals what you will find out when you measure its distant relative. Entanglement is a fact of nature, well-established by experiment. It suggests that time and space do not constrain quantum phenomena the way they do ordinary human activity. Among the latest intriguing aspects of entanglement to be studied involves black holes. It seems that black holes can be entangled, which apparently is equivalent to their being connected by a wormhole. Related work suggests that space, time and gravity are all part of a vast quantum entanglement network. Since both the evolution of networks and quantum entanglement fit nicely into game theory, solving all sorts of mysteries might boil down to viewing the world from a game-theoretical perspective. But maybe that will still be too hard for human brains — it might take advanced artificial intelligence, which, as this paper suggests, might be created with the help of some version of quantum game theory.  

Editor’s Note: It might not surprise readers to find out that Tom Siegfried is the author of a book about game theory. But he says the book did not include the sort of wild speculation that is suitable only in blog posts.

Follow me on Twitter: @tom_siegfried

Tom Siegfried is a contributing correspondent. He was editor in chief of Science News from 2007 to 2012 and managing editor from 2014 to 2017.

More Stories from Science News on Quantum Physics