The annual Edge Question Center has now gone live. This year’s question: “What is your favorite deep, elegant, or beautiful explanation?” Find the answers here.
I was invited to contribute, but wasn’t feeling very imaginative, so I moved quickly and picked one of the most obvious elegant explanations of all time: Einstein’s explanation for the universality of gravitation in terms of the curvature of spacetime. Steve Giddings and Roger Highfield had the same idea, although Steve rightly points out that Einstein won’t really end up having the final word on spacetime. Lenny Susskind picks Boltzmann’s explanation of why entropy increases as his favorite explanation, and mentions the puzzle of why entropy was lower in the past as his favorite unsolved problem — couldn’t have said it better myself. For those of you how prefer a little provocation, Martin Rees picks the anthropic principle.
But as usual, the most interesting responses to me are those from far outside physics. What’s your favorite?
Full text of my entry below the fold.
Einstein Explains Why Gravity Is Universal
The ancient Greeks believed that heavier objects fall faster than lighter ones. They had good reason to do so; a heavy stone falls quickly, while a light piece of paper flutters gently to the ground. But a thought experiment by Galileo pointed out a flaw. Imagine taking the piece of paper and tying it to the stone. Together, the new system is heavier than either of its components, and should fall faster. But in reality, the piece of paper slows down the descent of the stone.
Galileo argued that the rate at which objects fall would actually be a universal quantity, independent of their mass or their composition, if it weren’t for the interference of air resistance. Apollo 15 astronaut Dave Scott once illustrated this point by dropping a feather and a hammer while standing in vacuum on the surface of the Moon; as Galileo predicted, they fell at the same rate.
Subsequently, many scientists wondered why this should be the case. In contrast to gravity, particles in an electric field can respond very differently; positive charges are pushed one way, negative charges the other, and neutral particles not at all. But gravity is universal; everything responds to it in the same way.
Thinking about this problem led Albert Einstein to what he called “the happiest thought of my life.” Imagine an astronaut in a spaceship with no windows, and no other way to peer at the outside world. If the ship were far away from any stars or planets, everything inside would be in free fall, there would be no gravitational field to push them around. But put the ship in orbit around a massive object, where gravity is considerable. Everything inside will still be in free fall: because all objects are affected by gravity in the same way, no one object is pushed toward or away from any other one. Sticking just to what is observed inside the spaceship, there’s no way we could detect the existence of gravity.
Einstein, in his genius, realized the profound implication of this situation: if gravity affects everything equally, it’s not right to think of gravity as a “force” at all. Rather, gravity is a feature of spacetime itself, through which all objects move. In particular, gravity is the curvature of spacetime. The space and time through which we move are not fixed and absolute, as Newton would have had it; they bend and stretch due to the influence of matter and energy. In response, objects are pushed in different directions by spacetime’s curvature, a phenomenon we call “gravity.” Using a combination of intimidating mathematics and unparalleled physical intuition, Einstein was able to explain a puzzle that had been unsolved since Galileo’s time.
My favorite is the one liner mentioend by Carl Sagan years ago; “we are all ‘star-stuff'”. It’s a very simple but powerful statement of how a collapsing star creates the heavy atoms needed for life and for the rocky planets on which life exists (that we know of). There’s more to say on this but it is best said by Sagan himself in an episode of ‘Cosmos’.
Debra: I think its much more beautifully Sung, by Joni Mitchell in her `Woodstock’, beating Sagan by ~10yrs: “We’re StarDust…We are billion yr-old Carbon, & we got to get ourselves back to the garden”.
I second #12 and #20: Least Action and Noether’s theorem.
I really loved that I saw the scientific method on here.
Underappreciated and taken for granted, me thinks.
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Rolf Landaur’s explanation of why (and how) information is physical. Nothing is more intriguing to me than the eerie relation between something we used to think of as a product of our own reflective recognition and categorization of patterns, and the very real and unmistakable flow of energy.
My vote is for Shannon’s information theory.
I am not shure I have one.
But I can pronounce a couple of questions.
Can – theoretically- the strings or gravitones be the same as the dark energy dARK matter, if they were the first matter that scattered out from the BB- event and could they work as a “forcefield” pulling bringing the clumsier “ordinary mass” to or from its end station position?
I have two candidates for deep, elegant, or beautiful explanation. In probability theory, one explanation of data is the “Law of Large Numbers”.
http://en.wikipedia.org/wiki/Law_of_large_numbers
In the philosophy of measurement, one explanation of measurement is the “Law of Stray Numbers”. This law has been elegantly expressed by Shawn Achor as, “We know that’s a measurement error because it’s messing up my data.”
http://www.ted.com/talks/shawn_achor_the_happy_secret_to_better_work.html
Sean,
I’ve been working my way through Edge’s Deep/Elegant/Beautiful list, and about 20% of the entries have made me pause to learn more. There is lots of beauty and elegance out there, and my main ‘take-away’ so far is how lucky we are to be able to perceive and delight in it.
Also, ‘deep’ has new meaning for me. It used to be synonymous with ‘difficult’ or ‘obscure’. Now I see Deep as meaning ‘revealing’. A truly equal peer with Beauty and Elegance when defining the degree of satisfaction we feel concerning our attempts to explain our world.
I’m about half-way through now. Yes, it’s been weeks. But it seems things keep getting more interesting the further I go. A wonderful journey with many surprises along the way. My favorite surprise so far must be the results of combining statistics and graph theory with gastronomy. (No names or links: Look for it!) That simply tickled my brain in all the right places, and makes me want to be more adventurous in the kitchen.
Thanks!
The first definition given in Euclid’s Elements of Geometry: “A point is that which has no part”