h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

todaymueller, it is not "proof", but "evidence supporting" the theory of gravity.

i wasn't aware that gravity was only a theory . lifting my mouse off the mat and then letting it 'gravitate' back towards the mat is mighty strong evidence that gravity is in fact 'fact' .


best fishes .....tod

I don't believe that the law of gravity is fully understood,for a start gravity isn't constant and infact is directly linked to alcohol consumed,I hardly ever fall over when sober but I do fall over more often for each pint consumed-meaning that localised gravitational pull rises when it comes into contact with 'old speckled hen' and I don't remember seeing that infomation in any textbook

The reason why gravity is 'only' a theory is that while we know that it *does* work we don't know *how*.

RRrr yes, i can see where you are coming from there . when they start up the L.H.C. later this year . maybe we can then call it fact ?


best fishes.......tod

Probably not - cans of worms and all that.

In science, the word "theory" does not mean "random speculation". It has a totally different meaning. A theory in science is an idea backed up by a lot of empirical evidence. A theory is as close to fact as it gets, some theories have more evidence backing them up than others. So, gravity is both a theory and a fact.

When you say "only a theory" in a scientific context it really doesn't mean anything, like it does in the more common usage of "theory". Saying it's "only an untested hypothesis" would be equivalent.

Ste

Doesn't history tell us that that should read - gravity is both a theory and a fact at present.

I think that's implicit in the use of "is". But it's always good to point out that what is the truth in science is up to challenge constantly.

"gravity is both a theory and a fact."

Hmmm.
Doesn;t quite gel for me. Mainly because, I think, the gravity one is referring to when one discusses the theory is not the gravity that one is referring to when one discusses the fact. Gravity the fact is an objective (as far as we know) phenomenom in our reality. The Theory of Gravity is a model that gets quite close to observed reality for some aspects and completely misses out on other bits (whether we know it yet or not).

So I think that statement is a bit misleading.

Unless I've totally misunderstood what you meant by it, in which case apols!

Gravity is a very good example. As a theory it was not wrong, and continues to give accurate results when applied within a particular set of constraints. Einstein did not disprove Newton as such, he simply put the initial laws into context and described *all* possible scenarios. For most of us, Newtons laws work fine, as do the (false) assumptions that the flow of time is constant, matter is solid, the behaviour of objects is predictable etc etc.

The general public may well refer to these as facts; this definition will serve them perfectly well in everyday life.

Scientists on the other hand are well aware of what a theory is, but are extremely averse to using words like "fact" where there is scope for later meeja finger-pointing. Since so many laypeople seem to have trouble with the scientific meanings, I propose the following: when a scientist refers to a "theory", the layman should read "fact", with the caveat that the fact, like all facts, is subject to clarification, modification or complete negation as and when when new evidence comes to light.

In short, science knows what it knows with great confidence, but cannot always predict what it doesn't yet know. In a similar fashion, criminal law works on the principle of "guilt beyond all reasonable doubt", i.e. the conclusion is reasonable, given the evidence available at the time, with acknowledgement that it is impossible to know anything with absolute confidence.

"Gravity the fact is an objective (as far as we know) phenomenom in our reality."

That there is an objective universe out there is an underlying assumption of science. We cannot test it, but just hope it's correct.

Ste

yep ok i can see that there is a gap between what a scientist will call fact and what a layman will call fact . this is a problem when explaining things like evolution and global warming .allowing people with a vested interest like , creationists and oil companies , to exploit the percieved doubt .
with gravity the problem seems to lie with what is 'fact'for every day life and what happens on a theoretical or quantum level .
by the way the L.H.C. referance was a bit of a handgranade . it can be interesting to see the resulting carnege at times !

best fishes ......tod

<<
Doesn't history tell us that that should read - gravity is both a theory and a fact at present.>>

Not meaning to pick on WA in particular, I sort of picked this posting as typical of many. If we're trying to define fine distinctions of meaning between say, scientific theory and mathematical fact, shouldn't we be a tad more careful with our terminology and context?

Gravity is neither theory nor fact; it's a force empirically witnessed by most of us and currently postulated, enshrined and defined within the general theory of relativity.

Which leads quite nicely onto the next point. What do we mean by the word 'theory'? Well, taking the GT of R as an example, it's a self-contained internally consistent mathematical model of a defined subject territory. In this case, quite a big territory (the macroscopic behaviour of the universe) but it still has underlying assumptions and borders beyond which it starts breaking down.

Within its borders, it's actually quite a good model. But is it 'fact'? NO, of course not. We know it's incomplete because amongst many other considerations it has yet to be reconciled with quantum electrodynamic theory. Similarly QED, despite being within its own borders, possibly the most successful (accurate) theory yet devised, has yet to get any sort of handle on gravity.

So for theory, the key word is 'model'. Whether it's QED, GT of R, thermodynamics, optics or composting, each is a little island with its own language and 'legal system' of assumptions, postulates, definitions and 'laws', floating around in an uncharted ocean representing a hitherto undefined grand unified theory that physicists believe will eventually provide the answer to life, the universe and every thing. Let's call it the Sea of Gut.

For now, meaningful discussions about gravity can only be held on the island of GT of R. Anywhere else, it's just meaningless gossip. But even there, they know that there's no proof, not even a satisfactory explanation of what gravity is (and it's quite possible that there never will be one). But the consensus view of gravity on GT of R is the best anyone has at the moment, even if no-one totally understands it.

So how about 'Laws'? Well, laws are little more than a select few general observations that fall out of analysis of a particular field of theory, and hang or fall by the success of that particular theory against competing ones. Sir Isaac's Universal Law of Gravitation got repealed by Einstein just as Newton had repealed Kepler's Laws of celestial mechanics 250 years earlier. It wasn't that either Newton or Kepler were totally wrong, it's just that they were less totally right than Einstein, and the island had a small coup d'etat and name change.

And what happens when the Islands of Macronesia (GT of R etc) and Micronesia (QED, QCD) manage to pave over the Sea of Gut?

Two things.

1. The rest of us will find that the answer to life, the universe and everything adds a small but impossibly complex correction factor to our previous methods that we currently have covered by existing engineering tolerances. So we'll ignore it.
2. Many of the islands are in fact atolls. Residents of Fluid Mechanics Atoll couldn't really care less about the surrounding Sea of Gut; their big problem is Navier Stokes Lagoon in the middle of the island (flap of a Brazilian butterfly's wing and so forth). So we'll ignore it again.

So if there ever is such a thing as a general proof of anything significant, it's likely to be a bit of a damp squib for most of us, and probably totally incomprehensible even to the authors.

But if that's what you're looking for, I'm told that absolute certainties are readily available today at a Church near you

42

"Let's call it the Sea of Gut."

Aah, you've been to the Costa del English Tourist as well then.

i enjoyed reading that several times !!


best fishes .....tod

I've wondered extensively about his paradox:

The effect to most people of a these changes to GR and QED will be negligible. Governments spend huge sums of money building LHC (CERN) and LIGO, etc.

My explanation is that modern physics led to so many crazy things in the 20th century, that we have a chance of that occuring anew.