Why Do We Still Not Know the Reason Behind Gravity?

[bhobba]

Watching Star Talk.

Had some interesting questions/ideas - such as what makes you a scientist - they think its 100% curiosity but our education system damps that all important curiosity. 100% agree - but IMHO the more important thing is as Feynman says - the ability to doubt and constantly check from observation our current best beliefs (theories).

But one question really made me think. Do we know the why of gravity. The two astrophysicists there said - emphatically - NO - but we are working on it.

I went Hmmmm - not so sure. Isn't it space-time curvature and the principle of invarience. But is that why? In a sense, as I often say it's useless because if you know one why then you are faced with the why of that. But this is specifically gravity - is our current knowledge enough to give a yes or no answer - or - not really sure. What do others think? My answer is yes - but can be persuaded by others.

Thanks
Bill

 

[andrewkirk]

It depends both on exactly what the question is, and what the questioner would accept as an answer. As you point out, behind every answer there is another question: 'but why that explanation?'

To me, a natural interpretation of 'why gravity' is Newton's mythical question 'why does an apple fall down from a tree when its stem breaks?'

I think there is a satisfactory answer, which is: 'because, once the stem is broken, the apple follows its geodesic, which leads towards the surface of the Earth'.

The next question is 'why does the apple's geodesic lead towards the Earth?'

The answer is Einstein's equation, which describes the geodesic.

But the question after that is 'why does the universe conform to Einstein's equation?'

To which the answer is currently: 'We don't know'.

I expect that one day we will have an answer to that, in terms of gravitons, string theory, loop quantum gravity or some law not even imagined yet. But whatever that law is, the next question follows: 'Why does the universe conform to that law?'

 

[strangerep]

What do others think?

I'm in the "no" camp. The closest to "why" we can ever get in physics is when we have equations that account for all known experimental results reasonably accurately. But the astonishing size of the discrepancies labeled as "dark matter" show that we're missing something very significant.

See also the first quote below.

 

[jerromyjon]

I don't think physics answers any "why" questions, to be quite frank, so I say "no". If you just substitute "how" in place of "why" you get all the same answers, when available. Having gravitons or loops or strings will only give a better description of how, and still no reason why. Asking why gravity is always attractive would have a crackpot answer like "because massless particles always move at c", simply non-sensible to science.

 

[bland]

Feynman said it all in his 'magnets' interview. If one is not in a framework we one allows something to be true then one will forever keep asking why. The salient point here is that to not end up in an infinite series of why or how, then we must agree on a framework, but that's just for the sake of convenience, because the framework itself will have an endless series of why or how questions.

It's a bit like asking 'who am I', which really ends up dissolving into the hard problem of consciousness, nevertheless we all accept that when I say something that we don't treat every statement that contains the word 'I' as a philosophical enquiry for obvious reasons.