The One-Electron Universe

I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, "Feynman, I know why all electrons have the same charge and the same mass" "Why?" "Because, they are all the same electron!" And, then he explained on the telephone, "suppose that the world lines which we were ordinarily considering before in time and space - instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the pl...

 Bubble of Viral Spacetime

‘The achievement of the Kaminari-zoku implies that there are other spacetimes. Certainly other regions of the Universe beyond our causal horizon. If rational actors have evolved in them, they will have broken their Planck locks – or worse, evolved natively in an environment with no restrictions on computational complexity. If so, it is likely that they will have optimised the expansion rate of their spacetime, turned into an expanding bubble of thought. ‘If so, such a bubble of viral s...

 The Universe as a Simulation

‘Duh huh! That’s putting it mildly!’ Zinda purses her lips. ‘There are two problems, really. The first is that we can’t solve any hard problems. Not really. Anything that’s NP-complete. The Travelling Salesman. Pac-Man. They are all the same. All too hard. Even if we had a computer the size of the Universe! It drives the Sobornost crazy. We don’t mind it so much: that’s what makes most games fun. And we have quantum shortcuts for some special cases, like coordination. And for ...

 Plank's Constant

In the year 1900 Max Planck wrote down an equation, E = hv, where E is the energy of a light wave, v is its frequency, and h is a constant which we now call Planck's constant. Planck's equation was the beginning of quantum theory. It said that energy and {22} frequency are the same thing measured in different units. Energy is measured in ergs and frequency in cycles. Planck's constant gives you the rate of exchange for converting frequency into energy, namely, 6 × 10–27 ergs per cycle. B...

 Superstring Theory

It is time now to try to describe what a superstring really is. Here I run into the same difficulty which the geometer Euclid encountered 2,200 years ago. Euclid was trying to convey to his readers his idea of a geometrical point. For this purpose he gave his famous definition of a point: "A point is that which has no parts, or which has no magnitude." This definition would not be very helpful to somebody who was ignorant of geometry and wanted to understand what a point was. Euclid's notion ...

 Schrodinger's Cat as a Lock for a Box

Quantum mechanics claims that there is no definite cat in the box, only a ghost, a superposition of a live cat and a dead cat. That is, until we open it and look. A measurement will collapse the system into one state or the other. So goes Schrödinger’s thought experiment. It is completely wrong, of course. A cat is a macroscopic system, and there is no mysterious intervention by a magical observer needed to make it live or die: just its interaction with the rest of the Universe, a phenome...

 Nature is Intrinsically Probabilistic

Here are the circumstances: source, strong light source; tell me, behind which hole will I see the electron? You say, 'Well, the reason you can't tell through which hole you're going to see the electron is, it's determined by some very complicated things back here: if I knew enough about that electron - it has internal wheels, internal gears, and so forth - and that this is what determines through which hole it goes. It's 50/50 probability because, like a die, it's set sort of at random - and...

 On Naming the Quark

In 1963, when I assigned the name 'quark' to the fundamental constituents of the nucleon, I had the sound first, without the spelling, which could have been 'kwork.' Then, in one of my occasional perusals of Finnegans Wake, by James Joyce, I came across the word 'quark' in the phrase 'Three quarks for Muster Mark.' Since 'quark' (meaning, for one thing, the cry of a gull) was clearly intended to rhyme with 'Mark,' as well as 'bark' and other such words, I had to find an excuse to pronounce it...

 Metaphor for the Uncertainty Principle

There is a slightly flawed yet very satisfying physical argument that gives some heuristic understanding of the uncertainty principle. Quantum mechanics endows all particles with a wavelike behavior, and waves have one striking property: they are disturbed only when they encounter objects larger than their wavelength (the distance between successive crests). You have only to observe water waves in the ocean to see this behavior explicitly. A pebble protruding from the surface of the water wil...

 Neutrinos

Neutrinos were first predicted to exist as the result of a puzzle related to the decay of neutrons. While neutrons are stable inside atomic nuclei, free neutrons are observed to decay, in an average time of about 10 minutes, into protons and electrons. The electric charge works out fine, because a neutron is electrically neutral, while a proton has a positive charge and an electron an equal and opposite negative charge. The mass of a proton plus an electron is almost as much as the mass of a ...