Science Seen Time One author Colin Gillespie helps you understand the physics of your world.
Einstein and the Death of Physics
Motion is smooth, as any eye can see. In 1738, Scottish philosopher David Hume could―with little chance of challenge―say: ‘The infinite divisibility of space implies that of time, as is evident from the nature of motion.’ But physics now knows that, at scales far smaller than an atom, space isn’t smooth and motion must work in jerks. How will physics come to terms with this new picture?
In the 1600s, English physicist and mathematician Isaac Newton and German mathematician and philosopher Gottfried Leibniz independently invented math for smooth space, smooth time and smooth motion. Three centuries later Albert Einstein may have been the first to figure out that space may be made of tiny bits (quanta; Time One calls them flecks) that cannot be divided. Once you get your head around this, lots of things make sense but physics as we know it becomes history. Einstein figured that out too. In 1954 (less than a year before he died) he wrote to his friend Michele Besso:
I consider it entirely possible that physics cannot be based upon … continuous structures. Then nothing will remain of my whole castle in the air including the theory of gravitation, but also nothing of the rest of contemporary physics.
Many heavy dudes have since agreed. One of them, American physicist Lee Smolin, says:
Almost all of us who work in theoretical physics have failed to live up to Einstein’s legacy. His demand for a coherent theory of principle was uncompromising. It has not been reached—not by quantum theory, not by special or general relativity, not by anything invented since. Einstein’s moral clarity, his insistence that we should accept nothing less than a theory that gives a completely coherent account of individual phenomena, cannot be followed unless we reject almost all contemporary theoretical physics as insufficient.
So what’s the problem that some say is killing physics? In 1917 (the year after his now-famous paper on general relativity, which like almost all contemporary physics is based on a continuum) Einstein wrote to a former student:
The problem seems to me how one can formulate statements about a discontinuum without resorting to a continuum (space-time)… But for this we unfortunately are still lacking the mathematical form. How much I have toiled in this direction already!
Understanding the granularity of space is, he said, ‘devilishly difficult’. And flecks are so small there is no way to see them with even the best subatomic tools. But he didn’t say that we can’t see them; he said we don’t have the math. And since his time, as Smolin says, most physicists tend to be steered by math rather than to steer it by principle. Among those few who clearly choose to steer by principle, I’ll mention Greek physicist Fotini Markopoulou, Italian physicist Carlo Rovelli and, yes, American physicist Lee Smolin as pioneers of math and physics in the discontinuum with names like causal sets and loop quantum gravity.
Ninety-nine years ago general relativity joined quantum theory as Einstein’s main (and mutually inconsistent) legacy to physics. Is physics dying thanks to these two theories that, before he died, he saw as relics of the past? Or is it―thanks to him if today’s physicists heed his view of the future―looking for another leap in understanding?
David Hume (1738), A Treatise Of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects , London: John Noon, para. 188.8.131.52, p. 31; http://www.davidhume.org/texts/thn.html or http://www.gutenberg.org/ebooks/4705
Albert Einstein (1954), letter to Michele Besso, 10 August 1954, Albert Einstein Archives, The Hebrew University of Jerusalem, doc. 7-421; see also Colin Gillespie (2013), “The Curse of Continuity”, in Time One: Discover How the Universe Began, New York: RosettaBooks, p. 215, http://www.rosettabooks.com/book/time-one/, excerpt at http://www.timeone.ca/chapters/the-curse-of-continuity.pdf
Lee Smolin (2004), “Einstein’s Lonely Path: Surprisingly few theorists have the courage to emulate the master of modern physics”, Discover Magazine, Waukesha WI: Kalmbach Publishing, September; http://discovermagazine.com/2004/sep/einsteins-lonely-path
Albert Einstein (1917), letter to Walter Dällenbach, in The Collected Papers of Albert Einstein, Ann Hentschel (tr.), Princeton: Princeton University Press, vol. 8, p. 286; see also, Sabine Hossenfelder (2010), “Einstein on the discreteness of space-time”, http://backreaction.blogspot.ca/2010/10/einstein-on-discretenes-of-space-time.html
A sampler of other reading (technical, but you can get the drift):
Carlo Rovelli & Lee Smolin (1995), “Discreteness of Area and Volume in Quantum Gravity”, Nucl. Phys., Cambridge MA: Elsevier, vol. B442, p. 593; http://arxiv.org/pdf/gr-qc/9411005v1.pdf
Fotini Markopoulou (1999), “The internal description of a causal set: What the universe looks like from the inside”, http://arxiv.org/abs/gr-qc/9811053
Fotini Markopoulou & Lee Smolin (2004), “Quantum Theory from Quantum Gravity”, Phys. Rev. D, vol. 70, 124029; http://arxiv.org/abs/gr-qc/0311059
Fotini Markopoulou (2012) “The Computing Spacetime”, http://arxiv.org/abs/1201.3398
Carlo Rovelli (2013), “Relative Information at the Foundation of Physics”, http://arxiv.org/abs/1311.0054