Tuesday, August 18, 2015

The truth of Newton's apple

A comment on this morning's Quote of the Day from Isaac Newton prompted me to do a search for any evidence on the truth of what I had understood to be an unconfirmed legend, that Newton was prompted to develop the concept of gravity when an apple fell on his head.

It appears that there really was an apple, but Newton is more likely to have seen it fall perpendicularly to the ground, thus noting that it was moving towards the centre of the earth, than to have been struck on the head by it.

The previous classical viewpoint was that the apple and everything else would seeking it's proper locations. The proper location of the apple was on the surface of the Earth and the proper location of the Moon would be its' sphere, a set distance above the Earth. If removed from their proper locations, they would seek to return. Newton wondered why an apple's proper location would be in a tree while it was growing but then on the surface of the earth, and from this thought modern physics developed ...

I found a page on the New Scientist website here which refers to a manuscript now owned by the Royal Society (one of the manuscripts  available on the Royal Society website) which was written by William Stukely and would eventually become his book "Memoirs of Sir Isaac Newton's life."

Describing a conversation he had with Sir Isaac Newton in 1726, the year Newton died, Stukely wrote

"After dinner, the weather being warm, we went into the garden and drank there, under the shade of some apple trees...he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. It was occasion'd by the fall of an apple, as he sat in contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself..."
The other early references to the apple story (e.g. by people who met him or were at least contemporaries) are as follows according to Simon Fraser University's website, both published before Stukeley's book:

"Voltaire, writing in English in his Essay on the Civil War in France (1727), spoke of 'Sir Isaac Newton walking in his Garden had the first thought of his System of Gravitation, upon seeing an Apple falling down from the Tree'. He repeated the story in his better known and more accessible 1733 Letters concerning the English Nation (Voltaire, 1980) although in this work he spoke not of an apple but of 'fruit falling from a tree'. Voltaire's source was probably Catherine Barton.

The final early source was Robert Greene, on the authority of Martin Folkes, in his Philosophy of the Expansive and Contractive Forces (1727)."

(Incidentally I've taken the above quote about Voltaire and Greene on Simon Fraser University's site from the comments to the New Scientist online article linked to above.)


Jim said...

The basic premises is still there though. Anyone can and very certainly did see an apple fall to the ground.
I think its a very safe bet that people before hand had dropped things, or seen something else fall, always on a plum line to the ground.

the genius of Isaac Newton was to ask WHY? why does it always do that? why does it not go sideyways a bit sometimes? why does it always go straight down never up a bit first, and why when i throw it into the air as hard as i can does it always come back down again?

Of course from this we obtained Classical reletivity and Newtons Laws, which of course still do stand, its just they dont apply to the very very fast or the very very small.

Also we now know (post Einstein) its not the mass of the earth that attracts the apple, the mass of the earth warps the space time and the apple follows it direct line though time as it would have, but because the spacetime is warped it falls.

Though the basic idea is there as you pointed out "every great discovery starts with a bold guess" I would say its more akin to "every great discovery starts with the boldest question of all, which is WHY?, then you make a bold guess and then you try and try to prove it wrong, and if you can not prove wrong your bold guess, and no one else can (has to be repeatable by others) then well done, you just got your self a theory, that is one of the highest things you can ever have.

Chris Whiteside said...

Exactly: the first stroke of genius was to ask "why" and he then made progress by making a bold guess.

Jim said...

This is probably one of the best videos ever explaining gravity. Its so simple how he done it, but it does make the entire concept really easy to see and understand, and for a guy who normally does comedy he does a great job Enjoy.

Here it is