bust medical myths explore the latest science and answer all your burning health questions in every episode check out vitals in the link in the description and tell them that spacetime sent you our last episode was all about the principle of least action and how this one simple idea sort of leads to all of physics let's see what you had to say jsmith asks if the configuration space lagrangian seems to bridge quantum mechanics and relativity what's missing to make this a theory of everything rather than answer this myself i will read the reply by fernando the co-writer of that episode in simple terms the universe at its very core seems to be a set of symmetries which are manifest in the lagrangian this means that if we knew all the symmetries the universe follows we could describe it perfectly but we don't know all the symmetries and we're not sure how those symmetries fit with each other well put fernando it's the symmetries of the lagrangian via notice theorem that yields our conservation laws and well ultimately all of physics check our episodes on notice theorem quantum invariance and the electroweak force for some details but we probably need to go even deeper jackie johnson asks in the case of gravitational lensing isn't the light still traveling in a straight line isn't it space time that bends not the well that is a valid way to think of it light does travel in a straight line if you look at an infinitesimally small patch of space imagine light traveling through curved space as like an ant walking along a disco ball the ant's path around the disco ball looks curved even if it travels in perfectly straight lines across each mirror well in space the disco ball mirrors are infinitesimally small but over those regions the path is straight a few people pointed out an error i said that the action reduces to an integral over proper time in general relativity that was right but then i went on to call this a principle of least proper time by analogy to the principle of least action in fact in general relativity objects in gravitational fields tend to maximize not minimize their proper time that's still consistent with the whole action thing because the proper name for the principle is the principle of stationary action and the maximum is also a stationary point of proper time end of the action but i was still misleading so thank you for correcting me on that many of you point out that you're already adherents of the principle of least action as in you take the fastest easiest or laziest path to any outcome well me too like for example the effort i put into coming up with a joke to end every comment section
START_SELFPROMO_TOKEN bust medical myths explore the latest science and answer all your burning health questions in every episode check out vitals in the link in the description and tell them that spacetime sent you END_SELFPROMO_TOKEN