Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe | Lex Fridman Podcast #137

Alex Filippenko is an astrophysicist and professor of astronomy at Berkeley. Please support this podcast by checking out our sponsors: - Neuro: https://www.getneuro.com and use code LEX to get 15% off - BetterHelp: https://betterhelp.com/lex to get 10% off - MasterClass: https://masterclass.com/lex

the following is a conversation with Alex filipenko an astrophysicist and professor of astronomy from Berkeley he was a member of both the Supernova cosmology project and the high Supernova search team which used observations of the extra Galactic Supernova to discover that the universe is accelerating and that this implies the existence of dark energy this discovery resulted in the 2011 nobba prize for physics outside of his groundbreak can research he is a great science communicator and is one of the most widely admired Educators in the world I really enjoyed this conversation and I’m sure Alex will be back again in the future quick mention of each sponsor followed by some thoughts related to the episode neuro the maker of functional sugar-free gum and mints that I used to give my brain a quick caffeine boost better help and online therapy with a licensed professional Master Class online courses that I enjoy from some of the most amazing humans in history and cash app the app I use to send money to friends please check out these sponsors in the description to get a discount and to support this podcast as a side note let me say that as we talk about in this conversation the objects that populate the universe are both a inspiring and terrifying in their capacity to create and to destroy us solo flares and asteroids lurking in the darkness of space threaten our humble fragile existence here on Earth in the chaos tension conflict and social division of 2020 it’s easy to forget just how lucky we humans are to be here and with a bit of hard work maybe one day we’ll venture out towards the Stars if you enjoy this thing subscribe on YouTube review it with fast stars on Apple podcast follow on Spotify support on patreon or connect with me on Twitter at Lex fredman and now here’s my conversation with Alex filipenko let’s start by talking about the biggest possible thing the universe sure will the universe expand forever or collapse on itself well you know that’s a great question that’s one of the big questions of cosmology and of course we have evidence that the matter density is sufficiently low that the universe will expand forever but not only that there’s this weird repulsive effect we call it dark energy for want of a better term and it appears to be accelerating the expansion of the universe so if that continues the universe will expand forever but it need not necessarily continue it could reverse sign in which case the universe could in principle collapse at some point in the Far Far Future so like in terms of investment advice if you were to give me and then to bet all my money on one or the other where did does your intuition currently lie well right now I would say that it would expand forever because I think that the dark energy is likely to be just Quantum fluctuations of the vacuum the vacuum Zero Energy state is not a state of zero energy that is the ground state is a a state of some elevated energy which has a repulsive effect to it and that will never go away because it’s not something that changes with time so if the universe is accelerating now it will forever continue to do so and yet I mean you’re so effortlessly mentioned Dark Energy do we have any understanding of of what the heck that thing is well not really but we’re getting progressively better observational constraints so you know different theories of what it might be predict different sorts of behavior for the evolution of the universe and we’ve been measuring the evolution of the universe now and the data appear to agree with the predictions of a con density vacuum energy a z Point Energy but one can’t prove that that’s what it is because one would have to show that the numbers that the measured numbers agree with the predictions to an arbitrary number of decimal places and of course even if you’ve got 8 9 10 12 decimal places what if in the 13th one the measurements significantly differ from the prediction then the dark energy isn’t this vacuum State uh ground state energy of the of the vacuum and so then it could be some sort of a a field some sort of a new energy a little bit like like light like electromagnetism but very different from light that fills space and that type of energy could in principle change in the distant future it could become gravitationally attractive for all we know there is a historical precedent to that and that is that the inflation with which the universe began when the universe was just a tiny blink of an of an eye old a trillionth of a trillionth of a trillionth of a second you know the universe went whoosh it exponentially expanded that dark energy likee substance we call it the inflaton that which inflated the universe later decayed into more or less normal gravitationally attractive matter so the exponential early expansion of the universe did transition to a deceleration which then dominated the universe for about 9 billion years and now this small amount of dark energy started causing an acceleration about five billion years ago and whether that will continue or not is something that we’d like to answer but I don’t know that we will anytime soon so there could be this interesting field that we don’t yet understand that’s morphing over time that’s changing the way the universe is is expanding I mean it it’s funny that you were thinking through this rigorously like an experimentalist yeah but the what about like the fundamental physics of dark energy is there any understanding of uh what the heck it is or is or is this the kind of uh the the god of the gaps or the field of the gaps uh so like it there must be something there because of what we’re observing I’m very much a person who believes that there’s all always a cause you know there there are no um miracles of a supernatural nature okay uh so I mean there are two broad categories either it’s the vacuum Zero Point Energy or it’s some sort of a a new energy field that pervades the Universe the latter could change with time the former the vacuum energy cannot right so if it turns out that it’s one of these new fields and there many many possibilities they go by the name of you know quintessence and things like that but there are many categories of those sorts of fields we try with data to rule them out by comparing the actual measurements with the predictions and some have been ruled out but many many others remain to be tested and the data just have to become a lot better before we can rule out most of them and become reasonably convinced that this is a vacuum energy so there is hypotheses for different fields like with names and stuff like that yeah yeah you know generically quintessence like the Aristotelian fifth Essence but there are many many versions of quintessence there’s K Essence there’s even ideas that you know this isn’t something from within this dark energy but rather there are a bunch of say bubble universes surrounding our universe and this whole idea of the Multiverse is not some crazy Mad Men type idea anymore it’s you know real card carrying physicists are seriously considering this possibility of a Multiverse and some types of multiverses could have you know a bunch of bubbles on the outside which gravitationally act outward on our bubble because gravity or gravitons the the quantum particle that is thought to carry gravity is is thought to Traverse the bulk the space between these different little bubble membranes and stuff and so it’s conceivable that these other verus are pulling outward on us that’s not a favored explanation right now but but really nothing has been rul