Top 10 mysteries in science

Artist’s impression of a gravitational wave. Creative Commons Licence -

Artist’s impression of a gravitational wave. Creative Commons Licence –

I want to write something following the recent announcement of the discovery of gravitational waves. I’m not going to write about that discovery itself, because it’s all over the news. Instead, I want to ponder – what next? And in particular, which science mystery would I most like to be solved before I die?

I’m going to start with Physics, and stick largely to it, because I’m a physicist by training, and I know it best. But some of these questions branch out beyond Physics. Here are the ten big mysteries in science I’d like answers to:

1 What is dark matter?
Dark matter makes up the bulk of the matter in the observable universe. Its existence has been deduced by studying the behavior of distant galaxies, but it hasn’t yet been detected in the laboratory, nor is there any explanation for what it is. That’s embarrassing, frankly. Someone should do something about it, and quickly.

2 What is dark energy?
Dark energy makes up most of the energy in the universe and is causing the rate of expansion of the universe to accelerate. That’s annoying, because already 97% of the observable universe is now forever beyond our reach, even travelling at the speed of light. Thanks, dark energy! But perhaps we could do something useful with dark energy, if we knew what it was.

3 How can Einstein’s description of gravity as a warping of space-time be reconciled with quantum theory?
Einstein’s General Theory of Relativity describes how gravity works. Quantum Field Theory describes how the other fundamental forces of nature work. Frustratingly, these two great theories of the 20th century are fundamentally incompatible with each other. Grrr! That’s frustrating at an intellectual level, and it stops us from understanding situations where gravity and quantum effects are of the same order of magnitude – like inside a black hole, or around the time of the Big Bang. String Theory and Loop Quantum Gravity are two current theories intended to provide a consistent theory of quantum interactions and gravity, but they are both works in progress.

4 What is the explanation of quantum entanglement?
This is the mechanism by which pairs of quantum particles seem to be able to interact instantaneously with each other across arbitrary distances – an effect that Einstein called “spooky action at a distance” and which will drive you nuts if you spend too much time thinking about it.

5 What happened before the Big Bang?
So the Big Bang wasn’t the origin of the universe, but describes a state nearly 14 billion years ago when it was much smaller and much hotter than it is now. The current theory is that before the Big Bang the universe experienced rapid Inflation. But what happened before Inflation, or has the universe always existed?

6 Are we really part of an infinite or semi-infinite multiverse?
Lots of speculative theories in Physics invoke the idea of a multiverse. In quantum theory, the Many Worlds interpretation posits that the universe divides every time a quantum event occurs. That’s not a very economical way to run a universe, in my opinion. String theorists believe that our universe is one of a multitude of possible universes, and that each is equally likely to exist. But that’s just because String Theory sucks. Inflation theory suggests that our universe is just a microscopic bubble in an unimaginably vast sea of universes, and that’s quite probably true.

7 Is faster-than-light travel possible?
My head says no. My heart dreams of travelling to the stars. Faster-than-light (FTL) travel is theoretically highly problematic, because it breaks Einstein’s Theory of Relativity and opens up the door to time travel, which is self-evidently a thoroughly bad idea. But perhaps there are loopholes (or even wormholes) that we could use to travel to other galaxies, or at least to vacation in the Milky Way.

8 Is there intelligent life on other planets?
Statistically, there surely must be. But where? And what is it like? Will we ever meet intelligent aliens? If they exist within our own galaxy, we might meet them one day, but if they exist in other galaxies, then we almost certainly won’t, unless FTL travel is possible. So far, on balance, the evidence is that there isn’t any, otherwise aliens would already be here on Earth.

9 How did life on Earth originate?
Did it start here, or did primitive microbes come from elsewhere? Is simple life common throughout the universe? I feel that it probably is.

10 What is the origin of the laws of Physics?
This is the one I really want an answer to! Tell me now, god-damn-it! But I suspect we’ll have to answer most of the other questions before finding out. What I’m asking here is, how do sub-atomic particles “know” the rules that govern them? And why these rules, not others? I’d give anything to know the answer to that.

What about you? Is there anything you’d like an answer to? Do you want answers at all, or do you prefer the idea of a mystery?


48 responses to “Top 10 mysteries in science

  1. . . . and consciousness – what is it, or does it not exist? I thought that question was at the cutting-edge of unsolved mysteries Steve?

  2. Great post, with regards to your point 9.
    Despite over fifty years of searching for one , no extraterrestrial signal has ever been detected. It is becoming clear that the locality of our own galaxy is not full of advanced civilisations communicating with each other! My own feeling that intelligent life is rare in the universe.
    I talk about this a little in my post below

  3. OOps I meant point 8 not point 9 😉

  4. That’s a good list of questions. I doubt many will get answered any time soon.

    • I keep hearing rumours about a new particle being discovered at CERN, so if confirmed, that might be dark matter. There are certainly theories that potentially explain dark matter, so it might not take too long.

      Dark energy was only discovered a decade or so ago, so it might not take too long to solve either.

      The origin of life on earth might also be resolved in the next few decades, if we can capture a comet or two …

  5. An excellent list. I’d echo Hariod’s desire to understand consciousness. (At an objective level. I doubt we’ll ever cross the hard-problem divide.) I agree that it is computation, and we have possible insights into the algorithms, but I’d like to see enough evidence for us to actually know what those algorithms are.

    I agree that while simple microscopic extraterrestrial life may be prevalent in the universe, complex life is probably rare, and extraterrestrial intelligence is probably profoundly rare. So rare that it may be too far away for us to ever encounter it. (I hope I’m wrong.)

    “My heart dreams of travelling to the stars.”
    Even without FTL, I think it can still happen, but it requires us to look at developments which, though hard to imagine, are actually far less implausible than FTL.

    • Encountering an alien intelligence would be an astonishing experience, and it might well go very badly (for us or them, or both.) Perhaps it’s for the best if the only interstellar travellers we ever meet are humans returning home from the stars.

      • Oh, I didn’t mean to imply that I want them to come here. That might end very badly for us. But in the distant future, when we’ve spread far and wide, if we encounter another species, it could be a beneficial encounter, or at least not a catastrophic one. Of course, by that point encountering other branches of humanity’s offspring may be just as strange as outright aliens.

  6. I want to understand dark matter and dark energy. That’s a big chunk of everything that is unknown. It’s more interesting than the murder mysteries I read. I worry that I will be dead before the answer comes out. Or will it ever come out? Maybe death will be the big reveal. Something to look forward to?

    • I wouldn’t pin too many hopes on Death, but I’m pretty optimistic about dark matter and dark energy being explained in the next few decades. There is a lot of work being done in these areas right now, and plenty of hypotheses. We already know quite a lot about dark matter – it makes up around five-sixths of the matter in the universe; it does not interact electro-magnetically (which is why it’s dark); dark matter is “cold”, i.e. it is made up of heavy particles that are moving slowly (this rules out near-massless particles like the neutrino); it cannot be made of black holes or interstellar dust. So most people think that Dark Matter is made of WIMPs – Weakly-Interacting Massive Particles. Massive particles are hard to create in experiments like CERN, because they require very high energies. Being weakly interacting makes them hard to detect. But theories exist. For example, dark matter particles may be supersymmetric particles, and they may even be detected at CERN quite soon.

  7. number 1 is absolutely dark energy!!! dark matter is very little important element in the history of the universe!

  8. Most of those are philosophical questions rather than scientific and are more for pondering than for answering.

    • E.g., the origins of the laws of physics. The laws of physics are mental constructs. They are simply a way to explain reality. They exist as ideas, texts, and formulas. They originate in the human brain and exist only there.

      • I agree with you that the laws of physics are human constructs. But the question remains – why are they valid? Why does the universe behave in the way we observe? I think that only questions 6 and 10 are philosophical – the others should all be answerable using the scientific method.

        • The universe does not behave in the way we observe. We observe the universe to behave in the way it does. That’s a more correct way to put it. Then your question is “why does the universe behave the way it does?” This is a human question. Only humans can give “reasons” for their behavior. Isn’t this an anthropomorphic question?

        • agrudzinsky, I am a little baffled by your use of language. “Why does the universe behave the way it does?” is indeed a human question, as you say. In fact, all questions are human. But I think you may be conflating “reasons” with “explanations”. For instance, the ideal gas laws of classical thermodynamics are true because gas molecules have almost no interactions with each other. That is the “reason” gases behave the way they do. They behave like this regardless of whether any human is around to observe the outcome.

        • The question “why?” can refer to two things. One, it may refer to the events and circumstances leading to some current state (in other words, “how?” or “how come?”). Second, it may refer to intents and purposes. Your example is of the first kind. An example of the second kind is “why did the chicken cross the road?” Apparently, the universe does not have intents and purposes, so the second “why?” is not applicable to the universe. The first “why?” can be asked indefinitely with no ultimate answer: one could ask “why gas particles have almost no interactions with each other?”, etc.

        • Thanks for clarifying! Yes, I agree with what you say. In the case of why do gas particles not interact, it is related to their size compared to the volume that the gas as a whole occupies. Science is often about uncovering the “what?” and “how?”, but when this is done, we can ask the “why?”. This can still be part of science – it doesn’t have to be philosophy.

  9. Great post Steve!
    I have never gotten a satisfying answer to how Einstein’s General Theory of Relativity fully explains gravity. I get that mass bends space… so that an object could be accelerated in terms of direction…but what about velocity? If two objects are static with regard to each other, how does gravity make them START moving. I’ve never seen a satisfactory answer to this and I have seen prominent physicists say that it is still a mystery. It’s more “action at a distance.” [By the way, next Friday I’m going to meet Derek Mueller of Veritasium in Los Angeles at a presentation for his kickstarter campaign for an educational tool called Snatoms. I’m pretty excited about that!]
    With regard to the comment about consciousness above…I agree that it seems computational, but how exactly does the ego, the sense that “I am” emerge from that? The consciousness has to be greater than the sum of it’s parts (the individual nerve transmissions). It’s like our consciousness hovers within the gray matter that creates it. This is really mysterious! If computer scientists could ever discover how ego emerges in our human brains and could replicate it in a computer, that would be really scary. The computer would be afraid to be unplugged!

    • Craig, I think the misunderstanding arises because of the implicit assumption that objects move through space in a straight line. In fact, this is incorrect. Objects move through spacetime in a straight line.
      If a body is at rest in space, then it moves forward in time at a uniform rate.
      When a mass is present, the mass will curve spacetime such that the straightest path through spacetime is movement in space towards the mass, plus movement through time. The object’s movement through time will slow as it experiences acceleration towards the mass.
      None of this is intuitive, nor is it captured by the common analogy of an object bending a surface on which it is placed. You have to look at the equations to understand what is really happening, and the equations of General Relativity are horrible! Non-linear differential tensor equations – triple yuck!!!

  10. Craig, on consciousness, perhaps with an understanding of how consciousness emerges, we could be sure to build robots and computers that DO NOT have self-awareness. Otherwise, we would be building slaves to work for us.

  11. Oh, you guys have bullied me! Lets’ add number 11: How does self-awareness arise in the mind? What is the specific brain architecture that leads to consciousness?

    • Great! Your dials go up to 11. 😀

      We know a complicated enough network of the right sort seems to give rise to consciousness. It seems reasonable to think complicated networks of other sorts might also. As you know (from from a whole series of posts 🙂 ), I don’t believe consciousness can be replicated with algorithms. I believe it arises from “hardware” processes, not “software” processes.

      But it’s definitely a mystery!

      • Perhaps of equal interest is the question, “can a simple network of the right sort give rise to consciousness”? It was once thought that complexity was the key. Maybe complexity isn’t even a requirement.

        • Since the problem is more defined by what we don’t know rather than by what we do, anything is possible. I’m inclined to believe complexity is key, though.

          [thinking out loud…] Human thought is very complex, and that complexity has to come from somewhere. OTOH, the Mandelbrot is extremely complex but based on simple rules. (OTOOH, it’s impossible to actually calculate the actual M-set. Each point is a mini-Turing Halting problem. All in all, it’s a bullet point in my list: Why Mind Ain’t Algorithmic)

  12. “What about you? Is there anything you’d like an answer to? Do you want answers at all, or do you prefer the idea of a mystery?”

    I enjoy a bit of mystery, and I do believe there are mysteries we will never solve (and I’m okay with that). There are some physics mysteries that intrigue me as much as those on your list…

    There is the Naturalness problem and its close friend, the Hierarchy problem. There’s also the related Flatness problem. These, combined with our lack of a quantum gravity theory, make me wonder sometimes if we’ve missed some key piece of information or way of looking at things. I’ve always thought quantum physics had a bit of “Epicycles” to it.

    I’d also like to solve the problem of why people have so much trouble navigating four-way stop signs… o_O

    • Yes, in a way those are jigsaw pieces in the puzzle that is number 10 – why is the universe the way it is?

      “we’ve missed some key piece of information or way of looking at things”
      Agreed. I am 100% convinced that we have missed something vital and simple.

      • Someday some scientist will slap their forehead and exclaim, “We’ve been so blind!” 😄

        FWIW, although I’m not sure I give it much credence, the Virtual Reality explanation of reality is very compelling in how it does away with many of these problems. OTOH, it just pushes those questions to a higher level (but maybe they’re easier to answer there).

        At root, the whole question, “Why are we here?” (or as some prefer: “How did we come to be here?”) is a pretty challenging one. I read Lawrence Krauss’s notorious little book three times, and it seemed very hand-wavy to me. I came away no more enlightened after than I’d been before (which is to say, not much at all).

        Even being religious doesn’t help, because there’s the question of how God came to be.

        At some point you just have to accept that existence… exists. There’s some bottom-level somewhere. It can’t be turtles all the way down. It’s just really annoying not knowing whether it’s particles or strings or branes or loops or twistors or something we haven’t even thought of yet.

  13. Hi Steve. Interesting spacetime answer. So…just like there is a limit to how fast something can go through space (~300,000 km/sec), there is a limit to how fast something can go through time and that would be when you are not near any massive object? And so we are not traveling through time as fast as possible? Still, yeah. It’s WAY unintuitive how massive objects cause movement toward each other. Still, it’s better than trying to imagine “particles” (like graviton particles) that “carry” a force. And I’ve heard of particle physicists talk of such particles. Reality is weird. Almost as weird as the idea of God. When I was young and knew just a bit of science, I thought that the Universe was all quite intelligible and what you see is what you get. Knowing more science has just made me more mystified. In a good way. A beautiful way.
    Regarding consciousness…I know that “complexity” is actually a technical topic and I don’t know much about it. Another thing to explore.

    • Yes, our own rate of movement through time is slowed (by a tiny amount) due to the fact that we live on a planet. But in astronomical terms, Earth is not very massive and doesn’t have a big impact. If you get close to a black hole, time starts to behave very strangely! Similarly, if a particle approaches the speed of light, time slows, as you know.

      I find relativity theory entirely unintuitive, and the only way to grasp it is by solving the equations – which is tremendously hard! Even special relativity is hard, but general relativity is the hardest subject I ever studied.

      • So in fact GPS satellites need two separate corrections – one because they are travelling at speed relative to us, and one because the gravitational effects of the Earth are less in orbit. The effect is 7 microseconds per day due to Special Relativity and 45 microseconds per day because of general relativity!

  14. I think we have the best chance of answers question 8, or at least partially answering question 8. Astronomers are getting very good at finding exoplanets and identifying the characteristics of their atmospheres.

    It’s only a matter of time before they find an atmosphere in a state of chemical disequilibrium, indicating that there is life. Whether or not that life is intelligent… that’s going to be a much harder mystery to solve.

  15. Number 10 keeps me up at night! I’d love to see a history of different theories on the topic, if you’re looking for a blog project. I’m probably more interested in the tangential project of how we come up with physical laws and how they relate to physical phenomena (a la Feynman’s /Character of Physical Law/, but all aspects of the issue are fascinating.

    • It’s a fascinating subject in itself. Many physical laws are simple consequences of fundamental symmetries, and the basic principle that the universe looks the same for all observers, i.e. that there is nothing special about humans. But there are broken symmetries, and rules that cannot readily be explained as trivial – at least not with our present understanding.

      My hope is that as we continue to make progress in fundamental physics, new symmetries will be discovered, and it will become apparent that all of nature derives from a few elegant and simple principles.

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