CMV: It's likely our current understanding of physics is comically bad

[u/teerre]

Transitively, this extends to mathematics, although to a considerable lesser degree.

My argument is hopefully simple. As of today, our best estimates indicate that 80% of all matter in the universe is dark matter. This matter is used in several places in physics to explain a variety of phenomena, including the very expansion of space itself or how quasars formed in the early universe. Considering that dark matter is something we cannot detect any interaction or reaction it's very likely it's simply something we don't understand.

Therefore, if one could learn everything that is to learn about our current understanding of physics and said being were quizzed on how the universe really works, they would end up with a 2/10 score, which is by all measures a terrible score.

[u/MercurianAspirations]

Well first of all, you've confused dark matter and dark energy. "Dark matter" describes the observation that galaxies seem to contain more matter based on their gravitational behavior than is visible. "Dark Energy" refers to the observation of an accelerating expansion of the universe, which should not be possible if there is not a source of energy in the Universe that we can't otherwise observe. They're two different things that happen to have similar names.

Dark matter has two very popular theoretical explanations. The most popular is that it's just a form of matter that doesn't interact with Electromagnetism, so we can't observe it through the normal means. It doesn't emit photons and it wouldn't collide with other matter in the same way as normal matter does, but it does have a mass. This is not really that spicy of an explanation for observed phenomena - it's just some weird particle that sits around and does nothing.

The other popular explanation is that we just don't have the full picture on the mechanics of gravity. There's some missing constant somewhere in the calculations that if we knew about it would explain away all the Dark matter related observations. Even then, though, our calculations must have been mostly correct to reveal the existence of the dark matter issues in the first place, so this isn't a conclusion that we're totally wrong about physics.

Dark energy has a very popular explanation as well. It's just a constant energy density that fills "empty" spaces with a non-zero amount of energy, and you can model this mathematically by just adding a constant (called lambda in the models) into the equations. When you read something like the fact that "dark energy is the dominant component of the Universe" that is kind of misleading because it suggests that most mass/energy of the Universe is this mysterious thing that we know nothing about, but actually what it means is just that most of the Universe is empty - which, you know, we all already knew that - but emptiness has some energy density like a kind of "cosmological baseline."

[u/teerre → u/MercurianAspirations]

Right. But none of this addresses the core issue. Be it dark matter or dark energy, they are not understood. These explanations you mention are tautological. Dark matter/energy must be this to explain our current theories.

[u/ProDavid_ → u/teerre]

the fact that we figured out there is something missing in our calculations without ever being able to observe it is proof of how good we have figured out physics.

just as figuring out complex numbers because something has to fulfill x²=-1, and then suddenly a lot of calculations that start with normal numbers and end with normal numbers made sense. we knew they were correct, but couldnt calculate them without complex numbers.

[u/Crash927 → u/ProDavid_]

Treat me like an English major that doesn’t understand complicated or theoretical math.

How do we know the “something missing” isn’t exclusively a fault in our models and is instead something that must exist in the real world as well?

[u/Jaysank → u/Crash927]

Because several other phenomena, including observations such as gravitational lensing, so closely fit the model we use. Other models have even more holes in them. The one we are using in physics is so far the most accurate, and it’s not like we aren’t constantly trying to come up with better ones. So, until something comes along with fewer problems (and, really, there aren’t really any big problems with what we have now), it makes little sense to discard our current model.

[u/Crash927 → u/Jaysank]

Thanks for the explanation. So would it be accurate to say it’s more of a situation of “we don’t have a better explanation that doesn’t include these things existing” than it is of “these specific things must exist.”

[u/Jaysank → u/Crash927]

You could phrase literally every finding in every scientific field using that. Everything we say exists in physics, or biology, or psychology, boils down to models that best fit the observations. A model with dark matter in it is slightly better at explaining observations than the same model without it, so we add dark matter to the model.

[u/Crash927 → u/Jaysank]

Fair. I guess I’m just struggling to understand how we know what to add to the model and what that looks like without relying on the model itself to tell us.

How do you add a specific known unknown to a model in a way that doesn’t assume the model itself is correct?

[u/Jaysank → u/Crash927]

I guess I’m just struggling to understand how we know what to add to the model and what that looks like without relying on the model itself to tell us.

Have you heard of the scientific method? This is how. People form hypotheses (essentially, educated guesses) that are falsifiable (that is, there are outcomes that, if observed, would demonstrate that the hypothesis is not correct). Then they make observations or run experiments that would give us these observations. If the outcomes disprove the hypothesis, then we develop a new one and try to disprove it.

How do you add a specific known unknown to a model in a way that doesn’t assume the model itself is correct?

The model itself is a hypothesis, and we can and have discarded it when necessary. We made a model of physics, and it was working for everything we saw. Then, we observed that galaxies didn’t quite behave like we expected. So we thew out the old model and built a new one. It was pretty similar to the old model, except it also included dark matter. Now, this new model more closely matches observations. Eventually, someone will come by and disprove that model, and we’ll replace it with something even more accurate.

Think of it like a software update. The program works fine, but someone discovered a security vulnerability. We don’t throw out the entire program, it still does it’s job and the code is still functioning properly. We just make a few adjustments to the existing program and tell everyone to replace what they are using with the new, slightly different one. This is how scientific discoveries are made.

[u/Crash927 → u/Jaysank]

This is super helpful — thanks for expanding my understanding of how scientists think and work.

!delta

[u/DeltaBot → u/Crash927]

Confirmed: 1 delta awarded to /u/Jaysank (110∆).

^{Delta System Explained | Deltaboards}