When does a scientific theory have to be changed?

What is a theory

"Is the theory of relativity just a theory or has it become a fact?"

I was once asked by friends and then at the latest I noticed that something was going really wrong in communication between science and the public.

For me as a scientist, this question simply doesn't make any sense.

So a scientific theory is not what is commonly called a theory.

What is commonly referred to as the state of the art or scientific fact is everything scientific theories. Our computers, our cars, our antibiotics, are all based on scientific theories.

So what is it A scientific theory?

Well, there are some hurdles to overcome:
a) logic
Every law of nature and every scientific theory starts as an idea. In the language of science this is known as hypothesis. And first of all it has to be logical. Hence, mathematics is the language of science. Also because you can lie with mathematics, but that is discovered pretty quickly. (1) 2 + 2 is now 4 - completely independent of what your personal opinion is. A logical and mathematical description like here, for example, that distinguishes a scientific idea from some fantasy that someone slaps on their homepage.
b) Verifiability - reality check
A hypothesis only becomes a law of nature or part of a scientific theory if it can be verified. This means that it must always be possible to find a chain of events that can be described by this hypothesis (experimental confirmation). At the same time, there must be no events that contradict this thesis (experimental counter-evidence or falsifiability). There must always be a comparison somewhere between mathematical description and reality as it presents itself to us. If this comparison goes wrong or if it is not possible indirectly and in the distant future, the hypothesis is rejected as unscientific.
c) Consistency - No contradictions allowed
The laws of nature and theories must not contradict one another. If they do, it is a sign that something in the descriptions is not quite right. Because laws of nature are not structures that exist completely independently of one another, but are mostly related to one another and / or are based on one another. If something needs to be changed in one law, this always has consequences for a whole series of other laws. Strictly speaking, it is actually a consequence of a). Because logical statements are free of contradictions.

Particularly important here: There is in science No way the universal proof that removes all doubts. Science will therefore never rest on its laurels and say: The world is just like this. Scientists know that their descriptions are at best a good approximation of reality and that there will always be something we don't know. That may seem unsatisfactory, but it prevents science from solidifying in dogmatism and closing itself off to innovations. It could be called the ultimate Socratic view. It would also be pretty boring if there was nothing more to find out 😉 Even if some people think that precisely this openness to new ideas is a disadvantage and requires a security that will never exist and that they dishonestly neither themselves nor others Demand ideas.

At the same time, scientists are also pragmatists. This means that they recognize that their theories and laws cannot reflect reality down to the last detail, that they are “only” approximations to reality and that errors can occur. But as long as it works, they have no problem using the existing theories extensively and highly successfully in practice (e.g. in the form of computers, lightbulbs, televisions, etc.) until the next improvement comes along. (Of course this is all an ideal image. In reality, however, some scientists tend to wild speculations or dogmatism. Well, they are only human - hard to believe!)

Since Newton, Galileo, Kepler and others at the latest, everything that we can see and measure has been described mathematically using natural laws and theories.

This path works in two directions.
a) Inductive (first experiment, then natural law):
An apple falls to the ground when I let go of it. How can I describe this mathematically and in accordance with other natural laws? Does the law also apply to pears and wooden balls? Newton's law of gravitation not only explained the free fall of an apple, but also Kepler's laws, which describe the movement of planets.

b) Deductive (first develop natural law logically, then check with experiment):
Aristotle claimed that heavy objects should fall faster than light ones. Galileo Galilei has shown through keen thought that this cannot be the case. Instead, all bodies have to fall at the same speed, which he also checked experimentally.

See: Feather and apple in a vacuum.
It even works on the moon: pen and hammer on the moon.

Now we have to clarify the difference between a law of nature and a scientific theory.

A Law of nature mathematically describes a very specific process in nature, but without providing an explanation of why the processes are now so expire.

A theory on the other hand, there is the totality of natural laws which mutually condition, build on and explain one another and are based on as few basic assumptions as possible. The aim is to provide the most accurate and complete picture possible of reality. It is constantly being checked, adapted and expanded.

Hopefully this makes it clear that a scientific theory is pretty much the opposite of what is commonly called a theory. In common parlance, a “theory” can be wild unproven speculation.

In science, on the other hand, a theory summarizes the totality of our knowledge gained from keen thought and experimentation and represents the currently best approximation to “reality”. It can only be confirmed through experiments and never finally proven. There is simply no such thing as the concept of eternal, absolute, universally valid truth in science.

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(1) At least if you have a clue about mathematics ... But that's a different building site.

"Is the theory of relativity just a theory or has it become a fact?" I was once asked by friends and then at the latest I noticed that something was going really wrong ...