The twenty most important numbers

October 23, 2009 2:13 PM

In a talk (at TED) by Brian Greene on string theory he says that there are "there appear to be about 20 numbers that really describe our universe..." He lists a few in his talk, but what are the rest of of those numbers?

The pertinent excerpt from the talk:

And that question is this: when we look around the world, as scientists have done for the last hundred years, there appear to be about 20 numbers that really describe our universe. These are numbers like the mass of the particles, like electrons and quarks, the strength of gravity, the strength of the electromagnetic force -- a list of about 20 numbers that have been measured with incredible precision, but nobody has an explanation for why the numbers have the particular values that they do.


posted by bigmusic to science & nature (7 comments total)

here
posted by phrontist at 2:14 PM on October 23 [1 favorite]

Actually, a lot of the numbers in that Wikipedia link are probably not the ones that he's referring to. The Standard Model of particle physics has 19 numbers which have to be put into the model by hand, but when you do that you get what seems to be an excellent description of the forces that aren't gravity (electric, weak, and strong). Some of them have clear physical significance, like masses and field couplings (think of them like the strength of forces), but others are much more arcane, like mixing angles. Adding in gravity would surely require a few more parameters, but I'm positive that he's talking about these parameters.
posted by Schismatic at 2:43 PM on October 23

Whoops, meant to link to the section with the table.
posted by Schismatic at 2:44 PM on October 23

I'm assuming he's talking about the 25 Standard Model parameters:

• the fine structure constant
• the strong nuclear force coupling constant
• the Higgs mass (still unknown!)
• the masses of the W and Z bosons (mediators of the weak nuclear force)
• the six fermion masses (electron, electron neutrino, and their heavier counterparts)
• the six quark masses
• four independent matrix elements in two matrices that describe how the neutrinos and quarks oscillate from one form to another

plus the cosmological constant that quantifies the density of dark energy. Dark matter will probably require at least one more constant, but we don't yet know the details.
posted by hal incandenza at 2:48 PM on October 23

He goes into more detail in The Elegant Universe. There is also a NOVA episode.
posted by Loser at 3:42 PM on October 23

Here's an excellent summary of the 26 fundamental constants by John Baez.
posted by Johnny Assay at 3:43 PM on October 23 [1 favorite]

I should also note that the experimental status of these 26 numbers varies widely. We don't actually have a good experimental determination of at least 10 of them, and in fact we have no evidence at all that four of them (the independent entries of the Maki-Nakagawa-Sakata matrix) are non-zero.
posted by Johnny Assay at 3:50 PM on October 23