To explain, I’m just a big old ignorant layman, but with other scientific fields I at least CONCEPTUALLY understand how they came to their findings.
Like if a Geologist tells me something about rocks I’m like: “Okay, idk how geology works, but I assume you did some kind of experiments involving rocks so you probably know what you’re talking about.”
Or if a neurologist tells me something about the human brain: “Okay, idk shit about neurology, but I assume you did some kind of brain scan or took some brain samples or did some kind of scientific experiment thingy to know this stuff about brains. I don’t know the exact details but I can at least abstractly understand the process by which you learned this thing you’re telling me now.”
Then I’ll see some news report about some finding a theoretical physicists made and it’ll be like: “The Universe is made of strings! And also the sun is a black hole! The universe is shaped like a doughnut!”
And my honky ass is just like: “How the fuck do you know that shit? What are you looking at? How did you figure that crap out?”
Physics is a large domain, so this is like asking how modern medicine works. You should be as baffled about acetaminophen, according to your reasoning, as you are about dark matter.
As with all sciences, physics is speculation and analysis based on empirical data. When our speculative theories cease to line up with the data, then we speculate some more, sometimes in radically new ways. This was the case when quantum mechanics came about, to solve problems like the UV catastrophe which were not explainable with classical mechanics.