Science answers many questions but some questions test us because they are difficult by nature. They take us to the margins. Let’s look at some — why they test us:

At Big Think, theoretical astrophysicist Ethan Siegel discusses five puzzles of fundamental physics, solving any one of which “could unlock our understanding of the universe.” They are, how did the universe begin, what explains neutrino mass, why is our universe matter-dominated, what is dark matter, and what is dark energy?: About our universe as matter-dominated:

More matter than antimatter permeates the Universe. However, known physics cannot explain the observed matter-antimatter asymmetry.

The Big Bang produces matter, antimatter, and radiation, with slightly more matter being created at some point, leading to our Universe today. How that asymmetry came about, or arose from where there was no asymmetry to start, is still an open question, but we can be confident that the excess of up-and-down quarks over their antimatter counterparts is what enabled protons and neutrons to form in the early Universe in the first place.

Ethan Siegel, “The 5 greatest puzzles in fundamental physics” at Big Think (October 3, 2022)

No known science takes us behind the Big Bang when such initial conditions as the prevalence of matter were set. There we are into philosophy.

In another article, Dr. Siegel talks about the fact that our two descriptions of the universe, general relativity and quantum physics, work quite well but they don’t work together:

We don’t understand how to calculate gravity’s behavior at high energies, at small scales, near singularities, or when quantum particles exhibit their inherently quantum nature. Similarly, we don’t understand how the quantum field that underpins gravity — assuming there is one — behaves at all under any circumstances. This is why attempts to understand gravity at a more fundamental level must not be abandoned, even if everything we’re doing now turns out to be wrong. We’ve actually managed to identify the key problem that needs to be solved to push physics forward beyond its current limitations: a huge achievement that should never be underestimated. The only options are to keep trying or give up. Even if all of our attempts turn out to ultimately be in vain, it’s better than the alternative.

Ethan Siegel, “The fundamental problem with gravity and quantum physics” at Big Think (September 27, 2022)

That’s an especially troublesome gap — not just because the two descriptions should work together — but because our universe gets on fine even though they don’t.

And then there is time. Asked at the BBC: “Why does time go forwards, not backwards?”

Here’s the problem: when you zoom in to the level of, say, one water molecule colliding and bouncing off another, the arrow of time disappears. If you watched a microscopic video of that collision and then you rewound it, it wouldn’t be obvious which way was forwards and which backwards. At the very smallest scale, the phenomenon that produces heat – collisions of molecules – is time-symmetric.

This means that the arrow of time from past to future only emerges when you take a step back from the microscopic world to the macroscopic – something first appreciated by the Austrian physicist-philosopher Ludwig Boltzmann.

Martha Henriques, “Why does time go forwards, not backwards?” at BBC (October 3, 2022)

Theoretical physicist Carlo Rovelli notes that time is bound up with entropy, the growing disorder in the universe:

“It’s not that the world is fundamentally oriented in space and time,” Rovelli says. It’s that when we look around, we see a direction in which medium-sized, everyday things have more entropy – the ripened apple fallen from the tree, the shuffled pack of cards.

Martha Henriques, “Why does time go forwards, not backwards?” at BBC (October 3, 2022)

We perceive time as flowing like a river, yet it really doesn’t. We are the ones who flow. And there is no obvious answer to the question of why time flows only in one direction except that our universe started on that path. Why? Again, back to philosophy. Somehow a die was cast or a decision was made but that may lie outside science.

There is also the vexed problem that mathematician Peter Cameron terms: “the mind-boggling mystery of infinity:”

This has been so since the time, two and a half millennia ago, when Malunkyaputta put his doubts to the Buddha and demanded answers: among them he wanted to know if the world is finite or infinite, and if it is eternal or not.

Peter Cameron, “Infinity: the question cosmology can’t answer” at IAI News (September 23, 2022)

Infinity works fine in math but not in the physical world where it descends into absurdities such as Hilbert’s Hotel, which is always full yet can always accommodate more guests… That raises a question: Is the world in which we live a limited subset of an ideal world? Again, this takes us to the boundaries of philosophy. But we got there by math, not mysticism.

Along those lines, Why can’t things just disappear forever? At Ars Technica, we learn:

This one-two punch of determinism and reversibility means that, in terms of physics, information must be preserved during any process. It can’t be either created or destroyed — if we were to add or remove information willy-nilly, we wouldn’t be able to predict the future or read the past. Any loss or gain means there would either be missing information or extra information, so all of physics would crumble to dust.

There are many processes that appear to destroy information, but that’s only because we’re not keeping careful enough track. Take, for example, the burning of a book. If I gave you a pile of ashes, this would appear to be irreversible: There’s no way you could put the book back together. But if you have a sufficiently powerful microscope at your disposal (and a lot of patience) and got to watch me in the act of burning the book, you could — in principle at least, which is good enough — watch and track the motion of every single molecule in the process. You could then reverse all those motions and all those interactions to reconstruct the book. Information is not lost when you burn a book; it’s merely scrambled.

Paul Sutter, “Black holes can’t trash info about what they swallow—and that’s a problem” at Ars Technica (October 3, 2022)

In any event, information is immaterial. The ideas in the burnt (or rescued) book could take any number of forms, including ideas that just stay in your mind. Many of the most important things in our world are not material.

Siegel asks pessimistically, “Is theoretical physics broken? Or is it just hard? When you don’t have enough clues to bring your detective story to a close, you should expect that your educated guesses will all be wrong.” It’s fashionable today to talk about a “crisis in cosmology” due to issues like these. But it is a static crisis, if such is possible. That is, things could go on this way indefinitely.

Will another discovery resolve the questions, as so often in the past? Or are we reaching the edge of the things science can tell us — the territory of “Why is there something rather than nothing”? We can only research and see what happens, as the questions that science is expected to answer grow more basic and more profound.

You may also wish to read: A recent Big Bang debate: Sheer politeness underscores a shakeup. Takehome point: “Everyone would be keen to abandon the theory if there’s a better alternative, nobody’s married to the Big Bang theory.” Such sudden, widespread cosmological doubt is bound to have a major cultural impact even if it’s too soon to see how it will play out in, say, science fiction.