The Great Debate or How Big is the Universe?

[Music] good afternoon everyone welcome to a space book live from the SETI Institute in Mountain View California and and scattered around as we still are my name is Simon Steele I'm the senior was I'm not the senior astronomer I'm gonna talk to the senior astronomer maybe I want his job I'm the senior director of education and stem programs at the SETI Institute and joining me today is South Shore stack the senior astronomer at the SETI Institute and we are going to take a little journey back in time about a hundred years to Washington and the Smithsonian natural National Museum of Natural History it's gonna be the 26th of April 20 19 20 I'll get my my data and my Center is right and said that we are going to be looking at how the universe looked a hundred years ago and especially at about a debate that tries to determine exactly what the universe is and how big it is maybe to start with tell us a little bit about the state of the universe a hundred years ago if we were back in 1920 yes well to begin where the cars would have looked a little different but the universe of course was pretty much the same but our ideas about the universe certainly weren't the same to begin with if you said okay what is the universe that meant back in 1920 that meant the Milky Way galaxy the universe was one giant flattened disk of stars called the Milky Way and that was it that was the entire universe and but there were you know glimmers that maybe that wasn't quite right and that's what smile you know really sort of spawned this debate there was a it was a debate about the debate actually because some people were saying yeah this debate should be about relativity right Einstein's theories of relativity we're still new back then and but you know then they thought well the public isn't gonna understand that let's talk about the size of the universe okay and welcome everybody to this this debate on the debate on the debate if you do have any questions please do to send them in and we'll try our best to answer them let us know where you are watching in from and we have a viewer from Kurdistan already welcome so I so it seems though when we go back to nineteen twenty and the the Sun is back at the center of the universe in a sense you know it was sort of this whole Copernican idea or anti Copernican idea you know that where where is humanity where where are we in terms of the universe as a whole we've already been displaced from the center of the solar system but we're still in the center of the Milky Way center of the galaxy yeah I think everybody likes to think they're special so we were still special some people said yes we were still near the center of the Milky Way but the other big question was okay if the entire universe is the Milky Way galaxy how big is that right and you know it's it's often very difficult to work out how far away things are and in astronomy if it's something close you can just use the geometry that the Greeks worked out about 1300 years ago 2,300 years ago having trouble getting my millennium straight yeah so you could do that but if you're talking about something that's far away you know farther than the nearest stars even the nearest stars is hard you you can't just use that geometry doesn't work too well so you know there was a big debate about well how big is the Milky Way galaxy for those who are taking notes both of you you know the the Milky Way galaxy was figured at that time to be roughly 30,000 light-years across and as you say Simon the the Sun was more or less in the center of that so you know 30,000 light years for the entire universe and we're in this center not so bad I mean you know you have easy access to to the food markets I mean that that's still that's still a big galaxy you know and if you're putting things into perspectives you know how much you know how big Rhode Island is or England you know thirty thousand light-years that this is this is big so it's not as if we're talking about a tiny little you know solar system sized thing but when you get up to these distances it's very very difficult to measure how far away stars are and I think bad that's the problem isn't it so sip it just to get back into the discussion on the bait would you like to say little bit more about the protagonists in this debate who's in the blue corner and who's in the red corner yes indeed there were two these guys they weren't the original choices but they were considered to be the better choices eventually and one was a guy from Southern California Harlow Shapley he worked at the Mount Wilson Observatory is run by a Caltech and the biggest telescope up there at least in 1900 by 1920 it was about to change was the 60 inch reflector so that's a five-foot mirror if you lay on the mirror of that telescope not a good idea but if you've done it you know your feet would hang over the edge down sorry if that was in Southern California but in Northern California the guy was a fella by the name of Heber Curtis and he was using the Lick Observatory telescopes the biggest which was the Crosley reflector and that's a 36 inch mirror so if your big dog was lying on it you know his feet would hang over the edge these are by modern standards pretty small instruments but this was an all California program and these two guys were there to debate basically how big is the universe so so let's let's turn to technology happily in in in the red corner first of all and what was his basic argument and I know apparently he was under pressure because they had people from Harvard watching him this is almost a job interview for him I believe so so no pressure there so what was what was his basic premise yeah yeah you're right this was kind of a job interview for Harlow Shapley he did get the job by the way he was he was not a very accomplished speaker so he was nervous he read from notes his opponent Heber Curtis from Northern California he was Northern California versus Southern California the guy from Northern California was a pretty good speaker so he didn't need to use the notes and so forth and so on so in some ways he came across a little bit better but here was their points of view Harlow Shapley said look my job and what it is to is I studied the size of the Milky Way galaxies and I've been looking at these clusters of stars at all Beeler clusters and on the basis of assuming that they're all you know similar to one another you know they're sort of like I don't know Tigers they all kind of look alike right he was able to judge how far away these things were and he said the bottom line there is that the galaxy is not thirty thousand light-years across which was the common number but it's three hundred thousand light-years across that's a big difference okay that's what he was arguing and so he said you know these little smudges you find on on photos made of the sky with you know long time exposures these are little smudges they have to be inside our galaxy you know balls of gas discs of gas something because the galaxy is so big they couldn't be beyond that Heber Curtis from Northern California saying I think that's wrong he didn't argue about the size of the galaxy so much but he said those little smudges they're way beyond the edges of the Milky Way and those are other galaxies and we live in a universe in which the Milky Way is just one of many and he introduced some Island universes didn't he as a as a concept for the bees galaxies and that these are our Milky Way's in themselves but there's a problem of course with with that because we go back to for errors and bits in a minute but Harlow Shapley Zestimate I mean this is ten times bigger than the galaxy was before which if that's true at three hundred thousand light years across and these other smudges are also three hundred thousand light years across that puts these these other galaxies at incredible distances that people weren't happy with so I suppose I don't know is it is it almost time to bring in another person another technology set to try and answer these questions definitively and and the technology is or the the objects I'm thinking of is Cepheid variables and and the other name to bring into this conversation is Edwin Hubble yes well absolutely I mean this debate wasn't really a debate you know each of the speakers got something like thirty minutes to present their case and so one guy gets up in each other well these are the size of the Milky Way and and the next guy gets up and he says well yeah it may be big but I think these little smudges are galaxies Island universes remember island universe that's that's not something like a reality television show island universe just means it's another galaxy right because a galaxy was a universe back then it's just a semantic point all right so he was saying that and the question was well who won the debate and at the time people thought that probably Shapley won the debate in other words the the galaxy was so big those little smudges couldn't be external galaxies that would have been the wrong answer but to say that he won the debate is probably unfair and nobody really wanted to be but you're right three years later this guy Edwin Hubble who had considered a career as a wrestler professional wrestler as it turns out he wouldn't have had a telescope named after him if he had been a wrestler but he was making pictures of a nearby galaxy called Andromeda but it wasn't called a galaxy then was just the Andromeda never was just a cloud in the sky of stars and he found a variable star in there and that was the clue to figuring out how far away it was which he tried to do and came up with an answer that was I think like 750 thousand light years eight hundred thousand light years and that meant Island universes so see a little bit more about these B stars are called Cepheid variables after after the first star a bit type was found in the constellation cepheus and you know that's where they get their names from and these stars have have a property actually that has been so critical in our understanding of the universe since that moment and the first person to study Cepheid was was a woman astronomer Henrietta Leavitt who was at Harvard College Observatory and say a little bit about Sippy variables not the technical details but what properties they have that make these things useful right exactly if you want to find the distance to something and you have no other way to do it you can kind of assume how bright do you think they are and that'll tell you how far away they are now that doesn't mean they not make much sense but think about it if I take a hundred watt light bulb and I put it 10 feet away from me and I have a light meter or something and I measure how bright it is then I put a 20 feet away from me you know be 1/4 is fried because it's toys as far away okay so if you just measure the the brightness or something you might be able to tell how far away it is if you know how bright it is intrinsically it's interesting you know that it's a hundred watt bulb and not a 500 watt bulb by the way I'm going to point out that behind Simon there you see a bunch of galaxies I think that Stephan's quintet mid involved with it studying that particularly if you look at the the galaxies and we know it's a galaxy to the upper right there it's sort of two o'clock on Simon's head that's NGC 73 20 in case you need to address it by its name and the question for years was how far away is that compared to the other galaxies in that a picture and they all look about the same size so maybe they're all at the same distance wrong that NGC 7320 in the upper right there is 10 times closer than the other guys you know so even even 20 years ago we couldn't figure out the distances to galaxies very well but this is all a sideshow let me get back to Henrietta Leavitt she was indeed Harvard College Observatory you know you know they sent her down to South Africa to study the small magellanic cloud or whatever and she found these stars in that cloud Cepheid variables that would get brighter and then dimmer and then we'd get brighter and then they'd get dimmer and they'd get bright because they were different sizes it turns out but what she figured out was you could tell you know their brightness on the basis of how long it took them to get bright and dim right if they did it very quickly you know one day the bride and the next day their dim then they're bright again dimming and then they were kind of dim bulbs if they took days to get brighter and dimmer and they were very big stars that was the key for Edwin Hubble to figure out that Andromeda was eight hundred thousand light years away not that she gets much grant she was a woman working in astronomy and back in in the early part of the 20th century she was sort of overlooked at Chapel even went to havoc illusory and so and of course at Chapel is connection with with cepheid's as well because he you used and maybe use them don't quite accurately to even get his number for the size of the Milky Way didn't he yeah yeah I mean these guys would use of any techniques they could I mean some of them were very simple just by like saying as I just pointed out behind you those galaxies all look roughly even in a factor torso they all look pretty much the same size right so if somebody asks you okay you're driving up the freeway here and you see that car way up there how far away do you think it is you know without any instruments what you'd say is well it looks like it's about that big and I know how big cars are you know they're six feet across or whatever they are you look at them head-on that gives in your brain some idea of how far away it is so you know yes Shapley was using those arguments they all were I mean they they didn't have any other things to to go by but it was the case that with these little smudges which they were really trying to figure out the distance to they were all sizes on photographic plates and we now know the reason for that is the universe is filled with galaxies and some are near in summer farts and some look small and others look big so this was a first of all from the great debate and then from from Hubble's work this is a double whammy of the removal of humanity from the center of the universe isn't it because not only are we not the center of the galaxy in fact the galaxy isn't even the universe it's just one of 10 to the 10 known galaxies in the observable universe and then you know how big is the actual universe beyond the observable universe so it really was the beginning of the understanding of the sheer size of the universe and our removal about that special place in the center it's been called did this this whole thing where we found out that the universe had galaxies in and I think the current numbers like 2 times 10 to the 12 so that's like two trillion galaxies in the visible unit I mean that's a lot of galaxies pleasured right and it removed us not only from the center I mean there is no center and we're just another galaxy so philosophically now you know you could say all right this is the final blow it's you know we're just not all that special and of course it's possible that there's no real evidence yet that there are other universes and I can well imagine that 20 years to now let's say what are those guys talking about you know are there other galaxies come on there other you know it's a multiverse or all these other universes and we're not even you know the most important of the universes so you know when you walk through these to the shopping mall figuring you're really special reflect on this so actually most of the questions that have come in are about about the universe beyond the 1920's 1930's universe we've been talking about this is a question from Jerry and given given the relativistic nature of space and time what can we really say about the size on the age of the universe so tell us a little bit about the size in the age of the universe as we know it now in 2020 yes right well if I could say something yeah interesting there they probably fly me to Sweden for a prize right you know well not the age the age was originally actually worked out even Hubble could do that he said okay I found that the universe is expanding he found it out by mostly using other people's data but he was clever enough to to make a plot showing that the galaxies were all receding from one another mostly were and so you can imagine that it's like somebody you know close the pin on a hand grenade inside your living room never a good idea offense the host but if you do that you'll notice immediately they all you know everything is racing away from you all the fragments and all you have to do is measure the speed at which they're racing away from you you can work backwards run that movie backwards and now you know when somebody pulled the pin so they can see the age of the universe and that has been argued back and forth because of difficulties in the measurement for decades but the current number which is derived from very much more subtle arguments is roughly 13 and a half billion years so anybody in the audience who's watching this is more than 13 billion years old we'll remember the Big Bang in the start of the universe as far as the size all bets are off nobody knows I mean we can see obviously only things that are no farther away than about 13 billion light years because it hasn't been enough time for them for the light from those things to get to us we don't know how big the universe is some people think it's finite that is you could just count up everything and that was it here's the number there's how many galaxies there are and there other people say no but it's probably infinite and at this point I don't think we know and this is a subtle distinction between what we mean by universe with a capital u and observable universe because of the only way we can actually really observe the universe currently may be gravitational waves is another way that you know we can bring in is with light and that light travels at a finite speed and on the universal scale it's not very fast it's sort of just going a rather sort of slowest pace 300,000 kilometers per second which means that we can only see objects 13.7 billion light years away which is when that light was emitted and traveling to us now of course at that since that time those objects that have emitted that light have actually moved further away so so the actual physical space we're seeing is bigger than I think it's about 45 billion light years in rate something like that but who knows beyond that because we haven't got that information yeah exactly and and people will occasionally ask they say no way meant all right so you know nearby galaxies are moving away from us at a couple of hundred miles per second it was pretty pretty rapid clip but farther galaxies are moving away faster and if you look at the more distant galaxies I mean the ones behind you're moving away from us on the order of seven or eight hundred kilometers per second you know but if you look at the small little galaxies that are in that photo they're moving away from us at thousands of kilometers per second and eventually if you look far enough away they're moving at almost the speed of light but what about the galaxies beyond that because there surely are some like maybe most of them are they moving faster than the speed of light that sounds like something that shouldn't be allowed like you know going to the beach all right well then the thing is you got you you know you you're not you don't have the right body to is they used to say in Philadelphia yeah the point is that those it's not that the galaxies are actually moving through a big dark room right that the Big Bang was a little you know here got to pull a pin on this Hand Grenade and all these galaxies you know form and start expanding in a big dark room if they brought space with them space is part of the university if it also began with the Big Bang and it's space that's expanding not that the galaxies are moving through an empty space so they're allowed to go faster than the speed of light relative to one another so they're not actually moving is this the space between them is getting bigger killing us weird weird concept I like the like the you know the raisin pudding model right you know raisin pudding and you put it in the oven in all expanse and every reason gets farther away from every other reason it's good experiment to try at home never works a question from Rome an and maybe this is this is now we're talking about Hubble's work rather than shuffling Curtis but he talks about the Big Crunch now the Big Crunch is is is less talked about these days what is the Big Crunch and maybe that's something to do with food as well yeah no that's right it was always in my lunchbox it was always a Big Crunch there at the bottom no the Big Crunch was and particularly this is as you say somewhat of an antiquated idea but the galaxies are moving from away from one another but of course they're also all pulling on one another right they're the mutual gravity so they should all be sort of slowing down the expansion should be slowing down and the question is well will it just keep on slowing down but never get to zero or will it slow down get to zero reverse direction and then all the galaxies will come together in a Big Crunch and maybe just start another Big Bang and you know we'll come up with a whole new universe that depended only on you know the density of stuff in the universe but all of that has changed in the last 20 30 years because it you know there's something called dark energy that's blowing apart the universe much faster than we thought it's accelerating so it looks like the Big Crunch is not in your future you you know probably don't have to worry about that happening to you that you go out every night the galaxies are getting closer and closer until you're in a very hot fireball at which point all your real-estate investments are worthless so have a couple more people listening question from dawn how big is infinity we'll save that for the episode to Arlington Virginia so Paolo welcome Pakistan welcome to to listeners somebody from Poland as well let me see what's happening fors could black holes in our universe be the beginnings of big bangs for other universes I'll leave that one for you sir I mean people people like that idea but on on the other hand I mean there's something to it in the sense that making a big bang you may wonder how do you make a big bang it's gonna be your science fair project for next year apparently it's something that in theory you could do and maybe it happens in the extreme conditions of black holes possibly you know I haven't ever seen a paper which says black holes are the big bang's for new universes but there is something called you know continual inflation and so forth where in fact you you do make big bangs and in fact there's even a book I forgot who wrote it was some young woman physicists wrote a book on how to make a you know a big bang in your basement kind of thing you can make one at home what are the essential ingredients however if you don't need much it turns out but but you do need a magnetic monopole and without going into what that is let me simply say that if you have one at home write us a question from Nelson and we can see the the microwave background haven't talked about the cosmic microwave background which is the leftover heat from from the start of the universe from the Big Bang how much of the universe is visible and how much is it in invisible and and of course that's that's you know what do we mean by invisible I suppose yeah well that's maybe when people ask you what of what are the biggest science discoveries at least in astronomy in the past 30 or 40 years one of them of course is the fact that planets are very very common we didn't know that 25 years ago but now we do know that but the other things are the fact that there is dark matter in the universe right okay this is probably just some sort of elementary particles so you could say okay I don't care about that it's an extremely elusive I have to say nobody's found that particle yet but any that that's kind of a technical problem but the other thing that's real interesting now is the fact that the universe's expansion is speeding up right it's like somebody's leaning on the accelerator for the universe space is expanding not just fast but faster every second than it was the previous second okay and that's due to something called dark energy and we don't know what it is and again any listeners who have the insight on what this is and have published in a refereed journal by the way are welcome to get in touch because we could really use that info I think it's almost time to wrap up now so my question for you say if you are arranging a great debate now for 400 years later obviously we maybe wouldn't talk about the size of the galaxy or the the island universe what would be the topic you would choose for the great debates 2020 well in astronomy I mean obviously you could debate things like no I'll tell you it would be something analogous I would say is the idea of a multiverse right this is analogous to the debate 100 years ago is the idea of a multiverse just something with which to you know sell books and entertain people at dinner parties or is there any way to prove that it could be real good and on that note we will reconvene in 2130 21 20 rather thank you very much for the conversation that is wonderful way thank you very much for joining us everybody bye-bye

Channel: SETI Institute

Views: 7,030

Rating: 4.734694 out of 5

Keywords: SETI, astrobiology

Id: D-yc5xlKnf8

Length: 26min 3sec (1563 seconds)

Published: Wed May 06 2020