Can a scientific theory ever be absolutely proven?

I basically agree with Argus, though I take a slightly different perspective.

Physicists try to explain the world by constructing mathematical models to approximate it. The phrase mathematical model can sound mysterious, but it just means an equation or equations that predict what's going to happen given some initial conditions. For example Newton's laws of motion are a mathematical model, as is general relativity, quantum mechanics, string theory and so on.

Every mathematical model has a domain in which is a good description of the world, and within that domain we regard the model as effectively exact. Outside that domain we know the model fails. For example Newton's laws describe the motion of ideal particles at speeds well below the speed of light. We know that for higher speeds we need a different model i.e. special relativity, but this fails for high mass/energy densities. To handle high mass/energy densities we need general relativity, and so on.

So we describe the world using a range of theories i.e. mathematical models, and we pick the one that we know works for the situation we are considering. In this sense our theories are always approximate.

However within the domain of our model we are completely certain the model works. If you're sitting at a desk in NASA working out how to send a spaceship to Pluto you can be absolutely confident that the trajectory you calculate will work. You would not be worrying about whether some new and unexplained physics might send your spaceship spiralling into the Sun.

Simple Answer: Nothing is guaranteed 100%. (In life or physics)

Now to the physics part of the question.

Soft-Answer:

Physics uses positivism and observational proof through the scientific process. No observation is 100% accurate there is uncertainty in all measurement but repetition gives less chance for arbitrary results.

Every theory and for that matter laws in physics are observational representations that best allow prediction of future experiments. Positivism can overcome theological and philosophical discrepancies such as what is the human perception of reality. Is real actually real type questions.

The scientific process is an ever evolving representation of acquired knowledge based on rigorous experimental data.

No theory is set in stone so to speak as new results allow for modification and fine tuning of scientific theory.