The Sciences

The Effective Field Theory of Everyday Life, Revisited

Cosmic VarianceBy Sean CarrollJul 18, 2011 1:42 PM

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For some reason Nature News was inspired to tweet about my old blog post on Seriously, The Laws of Physics Underlying Everyday Life Are Completely Understood. Which I mentioned on Facebook, which led to an interesting comment, which I then mentioned on Google+... but now it's substantive enough that I feel like I am neglecting our loyal blog readers! So here is a copy of my G+ comment, and a lament that I suck at proper use of the internet.

Not sure what brought this back to life. Like the Lord of the Rings, this is part of a trilogy; don't miss the first installment, or the exciting conclusion. As Michael Salem points out on an alternative social-media site (rhymes with "lacebook"), some of the resistance to this really quite unobjectionable claim comes from a lack of familiarity with the idea of a "range of validity" for a theory. We tend to think of scientific theories as "right" or "wrong," which is hardly surprising. But not correct! Theories can be "right" within a certain regime, and useless outside that regime. Newtonian gravity is perfectly good if you want to fly a rocket to the Moon. But you need to toss it out and use general relativity (which has a wider range of validity) if you want to talk about black holes. And you have to toss out GR and use quantum gravity if you want to talk about the birth of the universe. Just because there is something we don't understand about some phenomenon (superconductivity, cancer, consciousness) does not imply that everything we think we know might be wrong. Sometimes we can say with confidence that certain things are known, even when other things are not. Not only do theories have ranges of validity, but in some cases (as with the Standard Model of particle physics) we know what the range is. Or at least, we know where we have tested the theory and where we can be confident it is valid. The Standard Model is valid for all the particles and interactions that constitute our everyday existence. Today we think of ourselves and the stuff we see around us as made of electrons, protons, and neutrons, interacting through gravity, electromagnetism, and the nuclear forces. A thousand years from now, we will still think precisely that. Unless we destroy the planet, or are uploaded into computers and decide that the laws of physics outside the Matrix aren't that interesting any more.

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