# The Meaning of Modern Physics

1. Sep 21, 2014

### jaydnul

In QM for example, I realize it is pointless to try and picture what is happening because the is nothing macroscopic to base it on. In GR, we are told that something called space-time is curved which creates the phenomenon of gravitational force. The deeper you go into these subjects, however, it seems that the simple explanation is never the case. Am I right in saying that gravity really isn't the warping of something called space-time, but it is helpful to think of it in that way in order to predict certain outcomes in our macroscopic world? If that's what modern science is all about, being able to predict certain outcomes in our macroscopic world, then what is the point of ascribing these pictures when fundamentally, that is not what's going on (other than to help the general public who have no intentions of further study).

From what I've gathered, a modern working theoretical physicist tries to formulate mathematics to predict the macroscopic outcomes of experiments that could be performed. That's great, but it really doesn't tell us exactly what's physically going on, and our unaided human brains probably could never understand what's going on, unless it involved simple Newtonian dynamics. Is that somewhat accurate?

2. Sep 21, 2014

### Staff: Mentor

It's always been that way. When Newton wrote $F=Gm_1m_2/r^2$ he was formulating mathematics to describe the outcomes of experiments involving falling bodies. That was great but it didn't tell us exactly what was physically going on - it just restated it in mathematical terms.

3. Sep 21, 2014

### Matterwave

The space-time curvature is so far the best picture and best explanation we have for gravity (General Relativity). But any physical theory can only be judged on its predictions, and not on its "picture". What can you "really say is going on" in any theory? Even in classical mechanics we have the two different "pictures" - Newtonian and Lagrangian.

4. Sep 22, 2014

### jaydnul

This might sound naive but why does that satisfy you?

Also, why do we have all these different interpretations of QM when at the end of the day, scientifically, we have what we need which is a predictive mathematical formulation.

5. Sep 22, 2014

### Staff: Mentor

That is a good question. Frankly, all of the worry and discussion about QM interpretations seems incredibly pointless to me.

6. Sep 22, 2014

### enorbet

Isn't that exactly the reason? ...to try to determine how the macro we know is built on the micro we don't know? Isn't finding that connection vital? We have grown used to rapid advancement and have no frame of reference for how long and arduous the crawl used to be in early work. In this frame, QM is but a baby, and babies get into trouble, make mistakes and messes, but in Science I'm betting everyone is aware of the retort "Of what use is a baby?" I think it applies here.

7. Sep 22, 2014

### Staff: Mentor

That's an odd juxtaposition of questions. The only reason that the curved spacetime formulation of GR satisfies is that it makes predictions that match our observations... just as does QM without interpretation.

8. Sep 23, 2014

### FactChecker

Einstein liked to use simple "thought experiments" to explain his theories. Take those seriously. They are correct, not just convenient.
No. The warping is completely correct as far as any experiments have been able to test it so far. Other, simpler, explanations have all failed. But those simpler explanations usually left some very serious questions unanswered (like, why is there a preferred inertial reference frame and who decides which reference frame is correct?). So they were not as complete an explanation as Einstein's is. The beauty of Einstein's theories is that, although the math is difficult, everything follows logically from a very small number of fundamental hypothesis.
The mathematics is based on hypotheses. When the math works out to verify experimental results, that supports the hypotheses that started it all. The hypotheses are the explanation, not the math calculations. Einstein's special relativity hypothesized that the speed of light is constant. The math that followed from that gave better results than anything else. The hypothesis "the speed of light is constant." is the explanation of what is going on. The math is just necessary to see what follows from that hypothesis, to make predictions and to see if experiments support or disprove the hypothesis.

Last edited: Sep 23, 2014