The Supermassive Podcast - 48: Do We Live In A Multiverse?

Episode Date: December 22, 2023

Izzie Clarke and Dr Becky Smethurst are rounding off 2023 with a biggie. Arguably the biggest of them all. This episode is ALL about the Multiverse. What is it? What does it mean? Does it even exist?   A big thank you to Andrew Pontzen from UCL and author of "Universe in a Box" for explaining the basics, Katie Mack from The Perimeter Institute for going from physicist to film reviewer, and to listener Wendy Entwistle who suggested the Supermassive team cover this topic. The Supermassive Podcast is a Boffin Media production for the Royal Astronomical Society. The producers are Izzie Clarke and Richard Hollingham. 

This is the Supermassive Podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Clark. We're married! I don't mind what's up with you. With me, astrophysicist Dr. Becky Smethurst. I'm going to have to do that again because I'm actually going to have to leave that in. Hang on one minute, let me regroup. Okay. And it's all about whether we live inside a simulation everyone just really wants wormholes to exist becky do you think we're in a multiverse hello and welcome to the super massive podcast from the royal astronomical society with me science journalist journalist Izzy Clark and astrophysicist Dr. Becky Smethurst. We are rounding off 2023 with a biggie. Like arguably

the biggest of them all is right this episode is all about the multiverse. What is it? What does it mean? Does it even exist? And we are going to attempt all of this in under an hour so wish us luck you're gonna regret that i know i know if we need to blame anyone we should blame listener wendy m whistle from canada who suggested that we cover this topic albeit over a year ago we got there in the end we got there in the end we got there in the end i mean surely there's an alternative universe where we did it immediately maybe yeah sure and with us is robert massey the deputy director of the royal astronomical society so robert when we talk about the multiverse is there an agreed definition as to what that actually means sort of yeah i mean the idea is the multiverse is or at

least could be this infinity of universes so just everything but even bigger than than a single universe which which itself is monstrously big too and it's it's a sort of massive science fiction staple and i think it's one level or another has been for a very long time you know even hg wells talked about sort of shadow universes. And perhaps appropriately for the Christmas party season, one of the first people to propose the scientific idea appears to have been a physicist, Hugh Everett, who did it as a PhD student in Princeton while drinking sherry. I have to say that I have never had inspiration at that level

while drinking sherry. I've talked a lot of nonsense while drinking sherry, but I've never come up with a theory of that grandeur. Well, you know what they say? They say you should code drunk, edit sober. So I'm sure there's an equivalent for the theory of physics as well. Ideas drunk and write it up sober. And you know what?

Christmas is just around the corner, so now is the perfect time. Now is the time. So you're right. I mean, this is what I've been missing. My career would have been so much better maybe this is why we leave Sherry out

before the Christmas as well you know because he's just cracked the multiverse ages ago and we're recognising his ability to

yeah that would solve the Santa speed problem wouldn't it really if you had he's in multiple places at once but it's a huge

staple and you know it's like Michelle you know everything everywhere all at once. You know, the idea that the many worlds idea, the idea that there's multiple copies of you is all fantastic stuff. That's what the multiverse is about. OK, well, we're going to cover the basics of the multiverse, if that is even possible. So helping us on our multiverse mission is Andrew Ponson, who's a professor of cosmology at UCL.

And I started by asking him to explain some of the more common theories of the multiverse. Let's take two different ideas around the multiverse. So one comes out from an idea about the early universe known as inflation. So inflation is the idea that very early on in our universe, the whole universe was expanding at an accelerating rate. And there is a fundamental question about inflation, which is what made it stop? And one possibility is that it doesn't actually stop everywhere at the same time. everywhere at the same time. So it might be that the very early universe is expanding in this weird way but then only some small part of it stops expanding like that and turns into more like a universe that we know and love today. And we sometimes call that a bubble universe. So you

can imagine a sort of a little bubble within this much bigger universe. And most of the bigger universe continues to inflate, continues to expand at this ever increasing rate. This is sometimes called eternal inflation. And it gives rise not just to one bubble, but to lots of bubbles. So you now have this picture where one bit of the early universe stops inflating, and then a bit later, maybe some other bit of it stops inflating and you get all of these different bubbles that stop inflating and they all effectively become their own separate universes so it's a universe is created as we have inflation and when that inflation stops that is one universe but if that inflation carries on, that then creates like another universe. And we

see that essentially keep going, as you say, over an infinite amount of time. I mean, what evidence do we have that might suggest that there is something in this, if any? Well, we don't have any direct evidence that this happens. So as I said a moment ago, the inflation itself is also sort of unproven at some level. And it sounds like a completely weird idea, but actually it was sort of invented in the 1980s for good reason. It was based on a number of things that we know about the universe. One is that it was once very small. Another is that the bits of the universe that we see, at least, seem to be very even and smooth. So a problem that we have with that is that if you imagine the Big Bang as this moment when the universe is created and it sort of all explodes out,

is the sort of classic picture of this, then you wouldn't really expect it to be uniform from one place to another. It would be more reasonable to expect the universe to be very different from one patch to another. And we know that wasn't the case. We know even today, if you look at the universe on very large scales, in some sense, it's quite similar from one place to another. And we can also look back through time. So we use special satellites, things like the Planck satellite, which tunes into the cosmic microwave background radiation. This is like a leftover echo of what was going on in the very, very early universe. And that shows that the very early universe was very, very smooth. And that's what gave rise to this idea of inflation. It's a way to kind of smooth out lumps and bumps in the early universe. It's based on quite an extrapolation of known

physics, but not a sort of completely crazy extrapolation of known physics. And it made some predictions, actually. It made predictions for what you should see in the cosmic microwave background lights, which then subsequently were confirmed by things like the Planck satellite that tuned into that light and showed us what it's really like. So there is some evidence that inflation really happened. And this idea of eternal inflation is not a huge step beyond that, because it's a fundamental question within inflation is how does it stop and and this seems to be quite a natural way to answer that so you can see that you know there's there's a bunch of ifs in there but it's not it's not so crazy that you shouldn't

give it any consideration at all yeah but if we think of these universes as as these bubbles is there a situation where two could collide? Yes. Is that theoretically a possibility? Yes, absolutely. This would be one way to really show that this had happened. If you could see some evidence that the universe that we live in, we can think of it as one bubble, but imagine that just next to it, another universe was born and it formed its own bubble.

And then in much the same way as when you're blowing bubbles out of you know soap solution you can get two that bump together and they collide and you see you see this sort of double sort of two spheres that have bumped into each other and there's a sort of circle where the two join in much the same way you could imagine seeing such a circle in something like the cosmic microwave background. That would give you evidence that something like this, some sort of collision of two initially separate bubble universes, had taken place. Now, we haven't seen anything like that to date, but people do carry on looking. These ideas are testable, but they're challenging to test. and so you know these ideas they are testable they're challenging to test yeah i mean we start my head starting to spin a little bit but i'm assuming you know in those in those bubbles

then you've got just different universes for the sake of ease let's say different people just living their lives and they're just two very separate universes but coexisting so you mentioned that there are there were two theories that you wanted to talk about. So let's talk about the other multiverse idea. What's that? Yeah, the other multiverse idea at first glance looks really different. And it comes from quantum mechanics, which is a really well verified theory of physics. I mean, quantum mechanics is definitely real, but it's also very strange. Yes, understatement of the age. Yeah, I mean, it's famously really hard to wrap your head around all the things that

are going on in quantum mechanics. Now, normally, we think of quantum mechanics as laws of physics that apply to really small things. So, you know, individual molecules or atoms or subatomic particles. And so, you know, then we start talking about the weirdness that goes on on those scales. If electrons or even atoms can be in two or more places at once, which we know they can, then why can't bigger things like, I don't know, a grain of dust or something bigger than that, know like a human being why can't a human being be in two places at once if all of the stuff that we're made out of can be in two places at once are we essentially saying like this is almost like parallel universes that there's two of me

there's a universe somewhere else where there's a different me doing different things is that is that what we're saying yeah i mean that things. Is that what we're saying? Yeah, I mean, that's exactly what we're saying. And once again, you know, I'll emphasise, we don't know this is true, but there was this very strange physicist called Hugh Everett who came up with a sort of solution to the fundamental question, you know, if an atom can be in two places at once, why can't we?

And his solution consisted of, actually, we can be in two places at once, why can't we? And his solution consisted of, actually, we can be in two places at once. It's just that that sort of hives off, at least to our perception, it sort of hives off into two separate universes. So you can never be aware of both of these things playing out simultaneously. And yet in reality, they can be. And so the reality consists then of multiple, perhaps an infinity of different universes all playing out simultaneously. The maths works, whether it's really true or not, well, that then starts becoming trickier and more debated. But if we understand that based on quantum mechanics, you know, it's this idea of, as we say, like the electrons being in two places at once. Are we always working in twos then?

Are we always looking at there's another me and there's maybe another you, but those alternate versions might not be in the same multiverse. Am I just massively overcomplicating this? No, no. I mean, so it doesn't have to come in twos. It can come in an infinite variety of flavors. So, you know, there could be infinite copies of me, if that's not too terrifying an idea. And also infinite copies of you and, you know, meeting and interacting in different ways in different universes. And in some sense, you know, this gives rise to the idea that all things that are not actually impossible do play out in some universe or another um and and so you know that is a slightly terrifying idea that everything everything that's not literally impossible is happening in some sense okay right and so i think one thing that we talk about, and maybe this has been emphasised in science fiction, is this idea of the possibility of travelling between multiverses. Are there any hypotheses behind that?

You know, is there any mathematical models that might say, oh, actually, maybe that would be possible? Or is that just completely fabricated? Yeah, this is where finally the physics sort of departs from the science fiction, I'd say. I mean, it's obviously it's a hugely attractive idea that we could travel between multiverses and experience different realities and get a chance to, you know, see how things might play out in a different world. There is no theory that I'm aware of that would actually permit that. So if we go back to that idea of the bubble universes, then we are stuck within our own bubble. We are not getting over to any of the other bubbles. And in this sort of alternative version of the multiverse, the quantum multiverse, you get to experience one universe, not the other ones. And there is no way to interact with the other ones. Almost

there has to be no way, because that is at the core of how it could seem like one definite thing is happening, even though, in fact, an infinity of different things are going on. Andrew Ponson, Professor of Cosmology at UCL. And so disappointing that you can't move between universes. Could you hear me feel my way through those questions? There was just so much to process. I was just going to say, my favourite part of that whole interview was just your valiant attempts to try and summarise what you just said for the listeners.

And I was like, you can do it. I was like, right, we do it I was like right we're gonna break this down we're just I'm all I'm you will hear me for the rest of this episode rather than talk about inflation cosmology it's just the bubble model okay talking about there's a lot to process in here like I don't I mean there is you can hear your brain wearing it and that's totally fine I think everyone else will feel akin with you this episode. Exactly. That's what I'm here for. But Becky, do you think we're in a multiverse? And if you do, which version of the two that we've talked about so far

do you think we could be in? I mean, I'd like to think we are, just so that there's a version of me being productive out there in the universe while I'm not. That's a nice comforting thought, isn't it? But I think the sci-fi sort of fan in me likes to think it might be the quantum mechanics many worlds explanation,

but the physicist in me leans towards the bubble model, as you put it, right? The bubble universe is in inflation. I think because inflation is already such a key part of the Big Bang theory, like it seems so familiar, like the idea that you know it's not that much of a stretch to then think about bubble universes with horizons forming in

something that we already sort of think well yeah inflation is what we need to give us the universe we see today it could also have given us bubble universes like that's my physics brain is sort of like yeah sure and given all I know about quantum mechanics, which admittedly is more than most, but still not a lot, still less than a few others. You know, quantum mechanics is all ruled by probability. And so I think the probability of like many worlds

is just vanishingly small. So the physicist in me reckons the bubble model is. Okay, okay. And a lot of people have been asking this so thank you to everyone who messaged us with this but the question that everyone wants to know is do you think black holes could be a gateway into other universes first of all let's just reiterate right that our best current understanding of black holes is that they are essentially like dark stars right you've taken the core of a star which is massive and heavy and has stuff and you have crushed it down until it's become so dense that light cannot

escape from there and you get this event horizon where you just get this sort of black region in the universe where there's no light coming from it, right? That's what we call a black hole. Now we don't know what's beyond the event horizon. It could be that you've taken the core of the star that was there and crushed it down so it's become some form of exotic matter that we don't know about. Or it could be that all the mass has been squished down into an infinitely small, infinitely dense point that we call a singularity. Like under our current current laws of physics we'll never know what's beyond the event horizon which i have had to come to terms with but we will never know right and i think one of those sort of two explanations though is way more likely than some other ideas that you know people have

raised as part of various different hypotheses that perhaps actually the singularity of a black hole becomes a white hole. So the exact opposite of a black hole. So where everything gets trapped in a black hole, everything can escape a white hole. You know, it's literally its exact opposite. And so people's ideas have been, well, if it becomes a white hole, it sort of exits into another universe, wormhole style.

And I will remind people that black holes we know exist, wormholes still hypothetical, right? And I think there's some people also that have argued that the fact that we've never found any white holes in our universe, we found, you know, billions to trillions of black holes, but never any white holes, which, you know, in terms of Einstein's theory of general relativity, like our best theory of gravity, like the mass checks out just as well for a white hole as it does a black hole. And so people have said, well, we've got, you know, trillions of black holes in our universe. Maybe it's because there's another universe out there that then has trillions of white holes instead. And the reason we don't have any white holes is because they're all in this

alternate universe. So it's interesting to think about that that could be the case. But given our limited understanding already of what is inside a black hole, I think it's a lot less likely than some of the other explanations, sadly. Everyone just really wants wormholes to exist and I have to be the person that's like,

I'm sorry, I just just we've no evidence for them i'm sorry to disappoint you everyone wants a black hole to go somewhere and i'm like no i don't think it'll be that fun all right we've got part two of izzy's interview with andrew coming up and of course there are more multiverses we need to talk through but to give everyone's brain just that little bit of a rest, just a little bit of a cookie in the middle of the podcast, we thought we'd have a bit of festive fun with one of my favourite people. Katie Mack is a theoretical physicist at the Perimeter Institute, and you might remember her

from our End of the Universe episode a few years ago. However, this time, being the very serious people that we are, we've asked her to review some science fiction films. And not just any science fiction films, the ones that depict a multiverse, and to explain if any of them got it even slightly right. A lot of the science fiction that uses the multiverse idea. And to a physicist, when we think about multiverse, there are lots of different ways we talk about the multiverse. And only one of them is the one that the science fiction has grabbed onto. And that's the kind of many worlds interpretation of quantum mechanics. And it's kind of always the same story to some degree. In different stories, there are different ways that it plays

out. Sometimes like in the Star Trek universe, there's like versions of the universe where all of the main characters are evil. Or, you know, a different group is in power in various ways. In Everything Everywhere All at Once, there are versions of the same people, but living very, very different lives, sometimes in cases where the humans are very, very different, or the rules of the universe are very, very different in some way. Or you have hot dogs for hands, for example. Yeah, exactly. But like the same people somehow. And, you know, and it's always this idea that, you know, you can kind of have something that changed, but a whole lot that's still recognizable. And I think that the place where that starts to seem less plausible to me, I mean, there's the jumping between universes part, which is also just not a thing that you can do.

But the idea that, you know, everything is different, except that, you know that you have exactly the same personality. I think that if you have a vastly different world with a vastly different history, it's going to change who you are. It's going to change remain the same. I think that that's one of the places where most of these stories become much less realistic. But also, it's not a very interesting story if there's just nothing recognizable in this other universe, right? So I understand why it's done that way. And then, of course, the idea that you can create a new universe that's had some decision point way in the past or that you can flip between universes that you can travel move your consciousness between them or something that's that's not something that that we think is possible in the many worlds interpretation okay and then another film that we thought we had to talk about was spider-man into the spider-verse am i right to assume that this again takes more of that sort of bubble idea the bubble sort of universe is how i'm referring to it i

don't know if it's explained in that film the origin of all these different universes i think the idea is that they have kind of different physics or different setups. No, it's just not really questioned, actually. Yeah. Yeah, and in that case, you have a universe that's a totally different kind of cartoon with totally different kinds of people, but there's always a Spider-Man in it. And again, it's just one of those,

it's a way to play around with a different setting and the same characters in some way or similar characters. It's a cool fictional idea but i'm not sure how well it aligns with any particular physical theory okay well we'll scratch that one off then and then are there any films that talk about a multiverse which sort of capture your interest and you think oh actually well that's a little bit different let's go into that a bit more well i think that the one that that i find to be done pretty well is the movie sliding doors in which there's a character who she's rushing for a train at some point and somebody kind of gets in her way and it's it's a real sort of split second chaotic random thing whether she makes it to the life, right? And it's an interesting film

because it's much more like the many worlds interpretation of quantum mechanics where there's a random event and, you know, different things can happen. And I think that's an interesting way of doing that. There's no portal where you bounce back and forth. It's just separate universes with a person who is changed by what she experiences, which also I think is a very interesting thing to see. So, I mean, I like the film in general. So I don't generally decide if I like a film based on how good the physics is. I don't expect a fiction movie to be you know perfectly physically accurate but i did i did think that that particular film did that kind of many worlds split very well thank you so much to katie mack then is i i feel like i mean we asked her about a lot of things

there yes like we didn't even mention rick and morty like that's the multiverse i know but where do you begin like what part of rick and morty do you even try and begin to analyze there's so much to unpack but anyone that hasn't seen it rick and morty is just an adult cartoon it's quite chaotic every episode pretty much involves a some sort of alternative yeah universe yeah it's like a granddad and his grandson just exploring the multiverse in random craziness. But I think what, I mean, you could point out, right, okay, there's a lot to unpack with Rick and Morty, but they do go for the classic, like, quantum mechanic,

many worlds explanation, just like most sci-fi. And it's kind of like the cartoon version of everything everywhere all at once, right? You know, except they portal gun to different universes rather than just, like, slamming into their different bodies. But as Katie said, I think it is sort of slightly less realistic in that way that you have the same people with the same lived experiences but just these slight differences to their to their universes you know so it's a bit yeah and it's a really interesting point though

when you look you see all of these films or these cartoons or whatever tv series everyone does have the same personality they are very much the same person they just look slightly different or whatever they've got hot dogs for hands the thing that made me laugh that i was thinking about the other day though was do you remember in um spider-man no way home and spoiler alert here for anybody who hasn't seen it i'm gonna ruin the major thing about the plot here is when andrew garfield spider-man turns up yeah through the portal and he says things like he's like he realizes the multiverse is real essentially but he says like string theory matter displacement it's all real i knew it kind of thing and i was i love the fact that rather than go for like the quantum mechanics many world explanation which

would be the like the physics that that Andrew Garfield would know, perhaps Marvel figured they'd just used the quantum explanation too many times by this point after Ant-Man and stuff. So they were just like, we have to give him something else to say. Give him other context. And they just went with, yeah.

So, I mean, I think we can probably rule out portal guns, not possible? can probably rule out portal guns. Not possible? Well, never say never is. This is the Supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Smedhurst, and science journalist Izzy Clark. Okay, back to the proper multiverse stuff.

No, I'm fine. So far, we've covered the many worlds model and the eternal inflation model. But there's another one that's a little more technology focused. And it's something that Andrew's latest book, Universe in a Box, is all about. I work with simulations of our universe. And it's all about whether we live inside what we call a

simulation. And the idea there is that we try to, in some sense, recreate some aspects of how the universe has formed and evolved inside a computer. And we're trying to get the computer to do the hard work of tracing through all the consequences of our physics theories and figuring out, okay, if those are true, then what should the universe look like? And this kind of idea of simulation has caught the attention of some philosophers and, of course, of science fiction as well. And it's given rise to this idea called the simulation hypothesis. And that's based on the idea, well, if we're able to make these digital replicas of reality inside our computers, then who's to say we're not actually living already inside one of those digital replicas? Who's to say that we are in sort of real reality?

Maybe we're just in some incredibly sophisticated simulation of reality and of course you know films like the matrix speak exactly yeah to that idea um and so this is this has got kind of some attention behind it recently with philosophers saying well you know actually yeah it's's really hard to rule that out. And some people go even further than that and say, actually, it seems pretty likely that we do live inside a simulation. And they have arguments for why that might be the case. And so in some sense, that then gives you another vision of the multiverse, because, you know, we live inside this universe and there is some outer universe out there that's beyond our reach or very hard to reach, which has those kind of massive computers that are creating our virtual reality. Why do people think that this could be true? Again, is there evidence?

evidence? In my view, there's very little evidence, in fact, no evidence that this is true. But the idea is as follows, that you imagine some far future extrapolation of the human race, where our computers are way more powerful than what we have today. And so they are just capable of performing simulations that mimic reality in a way that's basically indistinguishable. You just couldn't tell the difference between the real reality and the virtual reality. And then the argument continues by saying, well, first of all, you couldn't tell that you were inside such a universe. Not only that, but the thing about simulations is you can do lots of them. And in fact, that's exactly what we do in our simulations today.

We do lots and lots of them to figure out how might the universe have played out under different circumstances and with different laws of physics. So you imagine this far future version of ourselves, and we're just doing loads and loads and loads of these simulations. And then you do a counting argument. doing loads and loads and loads of these simulations. And then you do a counting argument. You say, well, then there's way more universes that are fake universes in some sense than there are real universes. And therefore, logically speaking, it follows that we live in one of these fake universes. So it's this idea that essentially there is almost like a parent universe that has set conditions for a simulation see how life plays out on that and that is one universe and then you know this parent

universe might set some other boundaries for how could life begin and that that one plays out and before you know it you've got just lots of different multiverses all with like slightly different starting conditions i suppose exactly yeah exactly that and um you know you you can then start to ask questions like well why why would we still why would we be doing this exactly and then you rapidly get sort of in a philosophical rabbit hole about all of this stuff but but i think you know that's the core of the argument now i i don't give this uh at the time of day really this idea part of part of the book was to explain why but in essence i think the problem is that it's just

too much of a leap that we're talking about such a huge extrapolation the universes that we try to simulate inside a computer today are incredibly lo-fi, if you like. They are so blocky and so rubbish compared to the amazing detail of the real universe. They can't even see individual stars, let alone planets, let alone life on those planets, let alone intelligent life on those planets. It really is a vast leap to go from the kind of things we're doing today to these kind of hypothetical far future simulations. And I think it's just taking too much for granted to imagine that we can actually make that kind of extrapolation to what scientists might want to do in this very far future with very different capabilities.

to do in this very far future with very different capabilities. Okay, okay. And so how careful do you have to be in how much you consider these theories or how much you dismiss them? You know, it feels to me personally, that it's a sensitive ground to cover and then you have to keep a level head to it to some extent. Yeah, you're absolutely right. I mean, I think you could you can sort of stray off the path in both directions. I think when we're talking about this kind of stuff, it's it's tempting sometimes as a scientist to be sort of overly dismissive of these ideas, because in terms of what the science actually tells us is definitely true. They are quite a long extrapolation away from that. And so it's kind of you know it can feel like or this doesn't really feel like science and it's sort of easy to poo-poo it and say it's just it's

just a load of rubbish the other extreme i suppose would be to kind of make those leaps that we've been talking about and not show you're working in between and go wow yeah i mean we live in a multiverse and isn't you know science has told us that we live in a multiverse. That's incredible. And treading that fine line in between where you say, OK, well, there are various different lines of argument that are leading us towards that. And there are ideas about how we could even test that idea. But at the moment, it's well beyond what we actually know to be true. That centre line can be a little hard to hit, but I think it's important that we do hit it.

Because if you're overly dismissive, it sounds like we're being too closed-minded about how we're thinking about the incredible universe that we live in. But of course, if you go too far the other way, then you start playing into conspiracy theories and things. So to cut the long story short, I completely agree. It's worth being really careful about how we talk about these things. And thank you again to Andrew Ponson. Becky, Robert, do you think we could live in a simulation? Personally, yeah.

I mean, you know, my simulation, I think this would definitely explain why I lose things and they turn up moments later, frankly. You know, there's somebody messing with the rules here. I think this would definitely explain why I lose things and they turn up moments later, frankly. There's somebody messing with the rules here. Yeah, I mean, every aspect of my life sometimes seems like it could be in a simulation. But yeah, I mean, seriously, I don't know. How can we tell? Isn't that almost the definition? It's just a philosophical question more than anything else.

I agree with Andrew that I think it's a bit of a leap. Like to go, like thinking in terms of how it's obviously very arrogant to think that you know humanity is the the peak of all advancement of technology but like thinking about how we simulate other universes like in the and like he said the the resolution you can get the resolution you would need for all these individual people like this and this simulation is is crazy i mean so just so i can sleep at night i probably tell myself no because like if we think about like andrew after you mentioned like the matrix right you know those who've seen

the matrix know that like they wake up from the simulation right but they're back in their own real bodies in in the real universe or whatever but if we are just in a computer simulation from a more advanced you know civilization there's nowhere for us to go we just exist in the computer so you know if someone presses ctrl c one day we all just stop that's a coding reference for everybody who gets it like you just cancel the simulation that that's it like nobody goes anywhere we just cease to exist so like it just seems like such a leap to think that's what we're in but like andrew's book is brilliant universe in a box like i can highly recommend it i really enjoyed it like i learned so much from it as well because

obviously my field isn't cosmology so it's just fantastic you know if you're looking for that last minute christmas gift or you've got a book token after christmas that you need to spend maybe andrew's book is a good idea okay noted so robert becky we have covered quite a lot in this episode but we've still got some listener questions for you both, so get ready for this. Although Carl Lumpden says, I was going to ask a question, but in another universe, you've already answered it, so glad you could help.

I'm going to be in church. Okay, well, as for the others, Robert Holly McFall asks, could other universes have different laws of physics yeah it's good it's good we're getting into the sort of brain melting questions at the outset here um yeah so holly the answer is that if you've got a motive is definitely yes because it's almost like no holds barred so one of the ideas is there are you know depending on the category max takemark physicists who look to this idea talked about four different types of universe and one is you know there's a bit of our universe that's so far away it's different then you've got universes with different physical constants and that's the kind of thing you're describing

and then you know we've talked about many worlds and the much bigger systems too but in that second category the idea that you have different physical constants different laws of physics yeah i mean why not it's an entirely different universe and the the upshot of that would be that they could be completely uninhabitable, that it might not be possible for stars and planets and then obviously life to form at all. So there could be an infinite number of these places where life simply isn't possible. So that then sort of implies that ours is a special case,

which is, again, another somewhat controversial idea. Is it a philosophical one or something deeper than that okay and becky samuel kandewal says if every universe is its own sphere or bubble why don't they attract each other with gravity so if we're thinking about the bubble model as you i love this is i'm going to call it this from now on we're thinking about the bubble model of bubble universes with inflation you still have this exponential expansion of inflation like between universes so obviously if we if we think about it as just a single universe of our universe like inflation has stopped here but if you have this sort of endless multiverse

then the inflation hasn't so that completely overpowers gravity and so the bubble universe is despite being you know a universe in size in mass like wouldn't be attracted to each other necessarily as for the quantum mechanics like many worlds explanation like we don't have a quantum theory of gravity yet so probably nobody could really say anything about this you might do later though if you get the sherry out yeah you might have one yeah get the sherry you know this is what we've been visiting all these years all the problems will be solved by the end of the day with the sherry but yeah i think if you're thinking about multiverses like many worlds

like you're making an assumption there that a that these multiverses are actually close together b that they are in causal contact as well and c that the forces from one would affect the other would transfer to the other you might have as robert just said like different physics in different universes of these many worlds um so you we just don't really know but having said that there is one idea that floats around that I quite enjoy. It's sort of an offshoot of string theory, which has sort of fallen out of favor a little bit. But it's this idea that if you think about gravity

compared to the other fundamental forces of physics, it's so much weaker. And you can demonstrate this just with a simple magnet and like a paperclip. You can hold up that paperclip with a tiny magnet despite the entire earth pulling down on it and i don't yeah i don't think people quite you know sort of register that when they have sort of like magnets that they're playing with so one idea is that because gravity

is so weak it must therefore be leaking into other dimensions or multiverses or whatever it is and as i said that mostly comes from string theory, that idea, which has maybe fallen out of favor a little bit in sort of recent years. So maybe we shouldn't put too much stock in that idea. But I think as we start to get into this, like, do multiverses attract each other? You know, it is something that you can think of. And maybe it's just the expansion that overrides this whole thing.

Interesting. Interesting. Okay, and Robert, I thought this was a good question from Balram Huber, and they ask, what evidence do we have against a multiverse? Yeah, I mean, Balram Huber, it's a fair question, really, and I thought when answering this, I thought, well, okay, the fact we haven't detected one, the fact the absence of evidence is not in itself evidence that they don't exist. But the fact we have no evidence for the existence of them means that, you know, the premise is, well, yeah, it's fair.

You know, there's no there's no evidence as yet, no direct observational evidence of the presence of other universes. So it's one of those areas of science, I guess, where you cross it. You definitely cross over into philosophy, into a lot of speculation. And personally, I think that's fine because it's well, you know, this is how science, I guess, where you definitely cross over into philosophy, into a lot of speculation. And personally, I think that's fine because it's, well, you know, this is how science advances. People think about deep ideas and then try them out. But it is one of those where I guess we might never be able to confirm it. You know, it may just be simply beyond what we're capable of doing, that there's simply no way in which we can check it. So then it forever remains this idea. And it links into things like the Copernican principle, the idea that somehow the Earth, the solar system,

the galaxy we live in, the universe we live in, none of these are special and unique. And why should they be? But yeah, we don't know. So the evidence, I guess, and it's not great, is that, well, we just haven't found any others. So at the moment you know you might as well say that they don't exist as much as you say they do i think it's worth saying that a lot of

things in physics have been like mathematically and like theoretically predicted before they were found like most famously like antimatter or even like neptune you know like the planet neptune was found we talked about right so i mean it's not unreasonable to think that one day you you could eventually find evidence and the only evidence she says in inverted commas right now is like mathematical but then there are people that we said like the cosmic microwave background could be the thing that provides evidence of multiverses if you have these like cold spots it could be that we're touching another universe and then you ask the question well is it just a matter of time before our instruments get good enough to detect

these kinds of things? Or is it, as Robert says, we may never have any evidence for, and we'll just never know. And I kind of hope it's not that one because it makes me sad. Yeah. So,

as with everything, we'll just have to wait and see. I'm a very unpatient person to have become a scientist. I'm just going to put that out there. Oh, brilliant. Well, thank you so much for answering those guys. And thank you to everyone that has sent in a question, not just for this episode, but for this entire year.

They're great, but do keep them coming. You can email us podcast at ras.ac.uk or find us on instagram at supermassive pod so robert let's finish up with some stargazing so what can we see in the night sky this month in this universe yeah i mean probably not evidence of multiverse would be my starting point god not yet not yet despite can you imagine citizen scientists from back garden discovers water after after drinking a sherry or two yes yeah right come on come on listeners we're waiting on you now we've got to do it we've got to do it so look yeah i mean look it's it's uh it's january right december into january so it's cold and it's dark but on the

other hand you've got these beautiful long nights you might not feel it but the earth is actually closest to the sun on the 3rd of january it's perihelion and of course that's the fact that you know seasons are dictated by the tilt of the earth rather than how close or far away we are from the sun because it doesn't vary that much but just to bear that in mind um and the days are getting longer obviously you know we slowly see those changes in sunrise and sunset times as we go through the seasons. But in the night sky, yeah, Jupiter is still dazzling after sunset. And the way, way up and really bright, really stunning object. Do have a look at that with a small telescope. If you've got a small telescope for Christmas, perhaps, you know, point at it, see those weather systems, look at the moons.

In the morning sky, you've got Venus still as well, at least for a few more weeks. Really, really obvious. You know, people still, you get up and you open your curtains and you think, oh, there it is, if you're looking east. But in terms of stars to look at, it's still very much the time of the winter constellations. So Orion and then down below that in the northern hemisphere, Sirius, brightest star in the whole sky is really prominent. And above those, the kind of the constellations of Auriga, charioteer gemini all of these are groupings with really bright stars in so they really stand out and they're also places that if you pick up a pair of binoculars or again you know if you point around with a small telescope there are

lots of nice targets too so uh lots of uh messier objects which are generally clusters and nebulae to look out for so without wanting to describe all of them in detail 35 36 37 38 41 and 50 all come to mind as very good things to look at and they're all clusters and uh you know because they're in the milky way beautiful clusters of stars so i should also say that we should look forward to the things we can see in 2024 as well and if you live in north america maybe in the us and mexico you're going to have a total solar eclipse in April, which I think a lot of people will be travelling for. It should be fantastic. Really good places like Texas, I think, is good for it.

And in October this year, we might, and I really hesitate to make these predictions because they can easily go wrong, but we might have a naked eye comet, quite a bright one called, well, potentially, Su-Chen-Shan Atlas. We'll see, you know, but it is likely to be good for the UK if it gets to be that bright.

And, you know, you never quite know. Predictions this far are always a little hard to make, but wouldn't that be fantastic? So we'll see. Oh, so good. The eclipse, I'm so excited for. I mean, I've got plans to go and see it. I haven't booked anything yet because I'm still waiting to find out

that if I happen to have observing time on a telescope at the exact same time I realised I was put in this application and it was like when do you want time for and I was like

dark sky new moon April I was like that's the eclipse so it's sod's law and like every email

that comes in this week I'm like because it's imminent like the decision and I really want to go but I also really want to see the eclipse and I'm like because it's I it's imminent like the decision and I really want to go but I also really want to see the eclipse and I'm like well silver lining either way right but this such is the life of an astronomer yeah and I honestly since our last

episode as well I've just been googling the sea star s50 telescope so maybe by October I will have saved up for one maybe we shall see oh the comet comets always surprise you though I bet there's another one that like pops up

at some point in the year that ends up being brighter than anyone predicted with zero notice yeah zero notice three days notice just suddenly

it's like oh you had plans want to drop them all to drive you know like two hours that way and go see a comet right on that note I think that's it for this month and in fact this entire year so we'll be taking a break for a few seasonal festivities and then we'll be back you mean sherry drinking and uh formulating physics purposes but we'll be back in 2024 with an episode about the end of the

world really you know putting the happy in happy new year. You know, it seems appropriate for January anyway, as I think you've picked right there. Obviously, contact us if you try some astronomy at home. You can email your questions to podcast.ris.ac.uk or you can find us on Instagram at supermassivepod. And we'll try and cover questions, requests for episodes, all of them in

future episodes in 2024 or i guess like wendy's request maybe it'll be in 2025 we'll see we shall see we're here anyway we're going to keep making episodes and we're looking forward to it we hope that you enjoy them too but until then everybody happy stargazing. Okay, but as for the others, Robbie, let's have... Robbie? Robbie! Oh, I love it! That's very familiar. Why is that for me? Oh, you merged Robbie and Becky, I didn't realize.

Robbie and Holly. I read Robbie and Holly at the same time. I don't know that I care. Does anyone ever call you Robbie? Um Do you feel like you're older? No not really When I was a kid I used to be called Bobby Which I hated

So do that Oh god Can you tell we're ready for Christmas