[krapp]

> Interesting, what's the definition of "physics model"?

A model which is based upon physics, which itself is (according to Wikipedia,) "the natural science that studies matter, its motion and behavior through space and time," and which, being a natural science, ascribes attributes and behavior to the material world and its processes through experimentation and mathematical inference.

>Also, can anything in written form not be called playing with words?

What "playing with words" means in the context of your former comment is that what you presented was a fantasy which ignored any of the observed and known principles (read: actual definitions) of the terms being used, and the science which led to them.

Alternative theories for dark matter are all well and good (MOND[0] is popular) but your alternative only makes sense if one neither knows, nor cares, about actual physics. We already know that planets are not clumps of electricity and light surrounded by a magnetic vacuum which is the medium in which information travels. That's not physics, it's word-salad, it doesn't even make sense.

That said, I still upvoted your comment because ridiculous as it is, fringe theories for dark matter aren't uncommon and they can and should serve as a basis for discussion, not just be quashed. It's understandable that people are uncomfortable or unsatisfied by dark matter and dark energy - particularly since the "dark" in those terms refers to the nature of the phenomena being unknown, and they seem counter-intuitive and humans (and perhaps CS/engineering types in particular) want the universe to not just be intuitive, but elegant and simple.

Unfortunately, the more we study it, the less sense it makes. To reference XKCD[1], the universe isn't built in Lisp, it's hacked together in Perl.

But that doesn't mean we should just throw out what we know and start again on first principles until we have a model that makes sense to us first, and describes reality second.

[0]https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

[1]https://xkcd.com/224/

[ta1234567890]

That was a very fair and insightful comment. I really appreciate you taking the time to respond intelligently and respectfully.

Now, regarding physical models, you are assuming there is a universal truth or reality that is the same for everyone. And that is just a belief. I don't think you can force anyone to believe something. You are also free to believe in whatever you want to believe.

[krapp]

>Now, regarding physical models, you are assuming there is a universal truth or reality that is the same for everyone. And that is just a belief.

There appear to be universal constants which can be experimentally verified and whose attributes and behaviors remain consistent. In other words, the universe appears to have properties which can be known. There is no evidence that the fundamental nature or properties of reality change based on the beliefs of the individual observer. Therefore, it is reasonable to assume that universal physical reality does exist, and that data gathered through repeated observation and measurement more accurately describes that reality than speculation without such evidence.

>I don't think you can force anyone to believe something.

Wasn't trying to. Just pointing out that the universe isn't arbitrary, and not all conjectures are equally valid. You can believe the moon is made of green cheese if you like, just don't expect to be taken seriously, because there is a vast amount of evidence that it isn't.

[tsimionescu]

The hypothesis that there is no universal truth is self-defeating. It isn't necessarily wrong, but any deduction you would make from it meaningless, and if you truly choose to believe you should fall into solipsism.

You yourself must believe in some universal truths, otherwise you would not attempt to communicate with other beings.

So, in order to have any kind of discussion, you must start from a point where you believe that at least a large part of everyday experience (including other beings, their minds, physical objects, their interactions, our observation thereof and many others) exist in a meaningful sense, outside your own cognition.

Now, any extrapolation from these base assumptions, is what we should think of as physics. For example, if I assume my eyes exist and my perception of the world is meaningful, then I must also conclude that the moon I see through a telescope exists to the same extent, and it's motion as I observe it exists, and I can search for explanations of that motion etc.

If I were to not assume that my eyes perceive something which truly exists, I would have no reason to stand in front of a computer screen, hitting keys on my keyboard and watching the letters appear on the screen - it's possible in a very absolutist way, but it's simply not a productive way of looking at the world.

[sls]

you say:

> regarding physical models, you are assuming there is a universal truth or reality that is the same for everyone

which is basically an axiom one must adopt to engage in science. E.g., here's the formulation found in the Wikipedia article "Philosophy of Science"[1]:

> that there is an objective reality shared by all rational observers

So if one wishes to engage in an inquiry that doesn't hold this axiom, it's of course a perfectly fine thing to do, but it's best for all concerned not to call it science or scientific. Many issues and lines of inquiry that are important to people aren't amenable to scientific inquiry, but it does nothing but harm to dissimulate.

[1] https://en.wikipedia.org/wiki/Philosophy_of_science#Naturali...

[ta1234567890]

Physics already acknowledges that there is no universal truth. Maybe not with those words.

All physical models depend on a "frame of reference". The most common one being the inertial frame of reference.

They do that because it all depends on how and from where you look at something, which is just another way of saying that the models depend on an observer.

Alternatively you could interpret that as there actually being some sort of universal truth, but then the experience of it is different for every single observer.

And then again, you are the one picking an interpretation or belief over another.

[jcranmer]

The terminology as understood in physics is not the same terminology that you're using.

The term "frame of reference" refers to how you have to set up the equations and how you define values, for example physical coordinates of a location. It doesn't change the actual predictions of the evolution of a physical system (and if it did, that's generally a good sign that the model is missing something!).

For example, you can model gravity in Newtonian mechanics on the surface of Earth as a force that pulls all objects down at a constant 9.8m/s^2 acceleration. Or you can step off the planet, and model the entire Earth as a closed gravitational system, and measure the gravitational attraction between the mass of the Earth and the things on or near its surface using F=G * m_e * m / r_e^2.

When you get to relativity, you discover that the problem is that spacetime is defined in such a way that there is no well-defined global "ruler" or "clock" that applies independently to all observers, so that 1 meter or 1 second for me on Earth is not the same 1 meter or 1 second on a spaceship travelling at 0.2c. What is independent to all observers is the speed of light in a vacuum, and from these two facts, you can in fact derive how to map the definitions of how your rulers and clocks would be distorted if you moved to a different reference frame.

[krapp]

The universal truth, in that case, is described by relativity. Different reference frames don't imply that the laws of physics differ between frames - in fact it's a fundamental axiom of special relativity that the laws of physics and speed of light are invariant (remain the same in all reference frames[0].)

[0]https://en.wikipedia.org/wiki/Special_relativity

[AnimalMuppet]

> Now, regarding physical models, you are assuming there is a universal truth or reality that is the same for everyone. And that is just a belief.

Can we prove that the laws of physics are the same for everyone? No. That's an assumption. It seems to be a reasonable one, but it's an assumption.

But we got to our current understanding of physical models from other ideas. [Edit: That is, other ideas of what the models should be.] How did we get here? By people believing other things, and them finding out experimentally that things didn't work that way, even for the people who believed that they did.

[yiyus]

Force is a strong word. But if your model can be verified by independent experiments and make useful predictions, it is more likely that it will be considered a valid model by other people.