Got a PM asking if I could explain this by an anonymous who frequents here so I'll put it here for others to enjoy.

Absolute truths in science are rare. 2+2=4, 20 kilograms is more mass than 2 grams, and there are four states of matter. That's just about it. Often one might hear statements like "the Theory of Evolution" or "the Theory of Relativity" and it can really sound like "Wow the science guys don't really know anything and are trying to teach it as fact! They're just guessing!"

That's because that first part is exactly what theory is. The confusion comes because the layman definition of the theory is not the same as a scientific one. In science, a guess that is testable is called a hypothesis. A hypothesis could be tested but it hasn't been just yet and it seeks to answer a question. A theory is the result of repeated hypothesis testing.

Lemme demonstrate.

Hypothesis: If I dropped two objects, then they'd migrate slightly towards one another because of an invisible force pulling them together.

I test it and sure enough, even in a weightless vacuum outside of the planet, if two objects that are left to move under no outside force, they will be accelerated toward each other until stopped by an outside force.

After repeated hypothesis testing on why this is true, a theory develops. That theory states that unless stopped by outside forces, two objects will be pulled towards one another through an effect called gravity. The power of said gravity scales with the mass of the object. All matter must thus have some amount of gravity and gravity is as inherent to matter as mass, volume, and density are.

This becomes the Theory of Gravity. This is because everything testable points in this direction and the theory can now be used to test new hypothesis and predict future discoveries because it holds up. For instance, if gravity is a truth and operates as theorized, which the theory assumes it is, and it affects all matter than one can make new hypotheses like this-

Hypothesis: If all matter has gravity and the amount of gravity positively scales with the mass of the object, then smaller celestial bodies will orbit larger celestial bodies because of gravity and not the other way around.

And sure enough the theory holds up. It might get more complicated with time, such as us finding that some matter seems to generate more gravity per volume than other matter does or that gravity can affect the light in some ways; but the theory still endures because there is nothing disproving it outright nor is there any alternative that is testable. Remember, science is only interested in the material world and can only work with in the material world. Proposing an answer that cannot be tested in the laboratory nor observed in nature is not making a new theory, just a statement that can't even be tested as a hypothesis.

Theory can also endure and be vindicated if it can be used to predict future discoveries. For instance, to go back to the Theory of Gravity, study of gravity allowed for the observation and discovery of numerous planets by checking to see which stars have a slight wobble in their movements. This is because smaller objects can manipulate the position of larger objects via gravity in tiny ways, like how a small dog being walked by its owner can still nudge them slightly. By checking to see which stars wobble in such a hypothesized way and in looking closer, new planets have been discovered!

And yes this is true with absolutely every single scientific theory.

The simple answer is because of the very big universe out therewith infinitely complex systems in a near infinite space. Nothing can be observed in its entirety. We can't watch absolutely every single individual of every single species on the planet at the exact same time to see if they change. We can't observe every single piece of matter in the universe to see if gravity affects it like it does everything else. We can't directly observe past events nor future events. We can't know everything, so we don't know if there may be some scenario where the theory doesn't hold up that also explains absolutely everything else.

However in everything we can observe, predict, test, and categorize; the theory holds up. It might change with the times to accommodate special conditions or unique mechanisms that were not apparent at first. But the theory endures because it encompasses everything we do know and what we can test. That's why it is treated as fact. It does include a bit of guesswork and never claims to be completely infallible as we understand it now, but it is anything but guess work.

6502963
and then there is this...
https://www.quora.com/How-can-we-make-2+2-5-1

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Granted that deals with most hypothetical math that is accounting for rounding, unknown variables, and additives in an incomplete sequence in which we only know of the "2"s being added with a result that is more than 4. In a nutshell, math in a complex system in which the result is known but the variables involved are near infinite.

In a nutshell, this is what Theory is. Taking what is known and using it to make sense of the end result.

6502963
Just goes to show how great and AWESOME our loving God is!!!!

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In a nutshell, this is what Theory is. Taking what is known and using it to make sense of the end result.

Eeyup!

Though, as you also point out above, since we can't see everything at once we can't be sure we have the full picture, thus, trying to absolutely (as opposed to relatively) prove or disprove anything by theory alone runs afoul of the possibility that something is missing.

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God is incomprehensible and that shows us just how small we are. I am firmly of the belief that understanding science lets one appreciate its work far more. Don't put God in a box and look at everything made and suddenly, across a nearly incomprehensible span of time and space that is creation, God becomes so, so much bigger.

Many great men and women have contributed greatly to our understanding of the natural world and sadly I see some aligned with Christian movements not grasping at how. Hence why I was correcting the term of "Theory" because the layman definition of "speculation" doesn't really fit. He or she who bashes a well meaning scientist for using the word 'theory' and not grasping at what that means is truly the fool.

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Which is the whole reason we say "theory" and not "law". As said, theory changes if it is not disproven, just adapted as understanding behind certain principles grows. For instance a theory on how a prehistoric animal might move can adapt or change because of the discovery of a trackway showing an odd manner of locomotion. Or the theory of gravity can grow to accommodate a new scenario discovered in which gravity behaves a bit differently than it normally would. A theory is only kept if it continues to make sense and if it disputed, such disputes are largely just because someone argues the theory is too simple and needs to account for extra variables, not because they think the theory itself is outright wrong.

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Again, Eeyup!

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Nice.