Katie Freese is a professor of physics at the University of Michigan, and the associate director of the Michigan Center for Theoretical Physics. Her work deals with a wide variety[…]
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A conversation with the University of Michigan theoretical astrophysicist.
Question: Does it make sense to ask what preceded the Big Bang?
Katie Freese: I think people have the misconception that the big bang is the universe starting from a point. In fact, it is very different from that. Probably you know that the universe is expanding, so if we go backwards in time then you can watch the universe contract as you go backwards in time. So for example, if you took a tabletop then any two points would get closer together, but the points that are way far apart if you had… Let’s say it’s an infinite tabletop, so as these points get closer and closer together you still have a tabletop that is infinite in extent. It’s not like everything comes into one point, but eventually you reach such a high density. Things are so compact and right on top of each other that we lose our description. Physics fails. That is what the big bang is, so it’s actually we would need to have a theory of quantum mechanics and gravity simultaneously to be able to discuss physics going backwards in time any further, so it is really a high density situation that we call the big bang, but there is really no explosion. There is no bang. There is no singular point. But so yes, it does make sense to ask well what happens when you reach that density and that is what people are trying to do in theories of quantum gravity such as string theory or well some of the cosmology that I’ve done also is in the context of brains where our observable universe is living on a three dimensional surface in a higher dimensional universe and there could be other brains out there and how these brains intersect one another and their motions and so on has been… So there are different avenues to try to pushback our level of knowledge and they are very active, but very difficult.
Everything was more dense and then there is a certain point where… which we call the big bang and it’s from that point forward that we start our clocks, so that’s… And then so and we say the universe is 13.7 billion years old is relative to that very high density situation.
Question: What are black holes?
Katie Freese: Inside the Milky Way and every other galaxy there is a giant black hole at the center and it is hard to explain where these came from, but even more peculiar is the fact that already at early times there are billion solar mass black holes. These weigh a billion times as much as the sun and this it at a redshift of six. Redshift tells you how much more dense the universe was at that time and so you have to in very rapid fire do something from forming these first proto stellar objects collapsing them probably to make… Before my work people thought you made relatively small stars and how you’re going to grow those up to making million and billion solar mass black holes is a puzzle and so one of the contributions we made was to say hey, but we think that the first stars can be quite a bit larger and then it would make sense for the large black holes to be able to form.
We think that these black holes grow by accretion, but the accretion is in a disk, so it is a flat ring around the black hole, so the stuff is swirling around in the accretion disk and it is moving pretty rapidly and before it falls into the black hole it’s giving off radiation, so what you’re looking for is the radiation of this stuff that is falling into the black hole and from studying that in addition to what you’re already saying about the motions of other things around the black hole you can infer that the black hole should be there.
Question: What is dark matter, and how does it affect our picture of the Universe?
Katie Freese: the galaxy is and in fact, the universe as a whole have the… they’re made of different pieces and the atomic matter actually is only a very small portion, so the rest being the dark matter. In fact, it’s kind of… It’s revolutionary over the past decade that this had become clear that if you add up everything that we’re familiar with on a daily basis such as your body, the walls, the planets, all these things, all the atomic matter only adds up to 4% of the total content of the universe and the other breakdown is in terms of dark matter and dark energy and right we’re talking about the dark matter, which is the predominant bulk of the mass in the galaxies and clusters and so on, so when people study these first stars they were aware that they form inside these big globes of dark matter and at the center of this… of the dark matter you have a proto stellar cloud of hydrogen and helium that starts to collapse, so our contribution was to say well but what about that huge bulk of material that’s out there, doesn’t it play a role in this star formation process especially because these first stars are forming smack in the middle of these… These spherical regions are called halos, so these halos of dark matter, especially near the centers is where a lot… there is a huge amount of dark matter in there and that is where your star is forming, so what we think happens is that there is a kind of dark matter power basically.
The dark matter particles and the ones that we believe… There is a lot of experiments going on right now to try to detect these particles and I think that it is going to be resolved in the next five years, ten years at most and the most likely candidate they’re called WIMPs, which stands for weakly interacting massive particles and these WIMPs whenever there is two of them that find each other they interact among themselves and they actually annihilate, so they lose their original identity and they turn into something else, but in that annihilation process dumps a lot of heat into this proto stellar material, so you’ve got this proto-stellar cloud that is trying to collapse to make a small star, but all of the sudden you’re stopped because you have this heat source that stabilizes the cloud and prevents it from collapsing anymore, so and it is actually really a star. The nomenclature dark star could be a little misleading in the sense that people think well it is probably made of dark matter, but it really isn’t. It’s really made of hydrogen and helium and just a smattering of dark matter. It is a very powerful heat source and less than 1% of the mass is dark matter and the annihilation process gives a heat source that powers the star and it shines. Very bright objects, they really are stars, so they’re atomic objects that shine due to the dark matter power.
Question: Do you think the Universe has evolved in a logical way?
Katie Freese: Wow, I think if we try to write down a universe on a piece of paper that was the most simple and the most elegant there is a lot of things you wouldn’t find, so if all the way… all the details intermesh, are very important to for example, allowing people to exist and I mean on the biological level I guess this is obviously that we’re very dependent on respiratory system and all the rest of it, which is not something that you would just invent again if you had a random piece of paper and certainly what we’ve discovered, this sort of pie picture of the universe that you have 4% atoms, dark matter, which I think is the… That is a solvable problem. I think we’re on the edge of solving that one, but then all the sudden this dark energy appeared as a complete mystery. This was on the late 1990s, so I think I was saying around… In the past 10 years, around the turn of the millennium it’s really been the golden age for cosmology from the point of view of data coming in and really affecting our thinking, so this is a very bizarre, probably illogical thing from our current understanding of what powers the dark energy, so the thing that we see is that apparently the universe is not only expanding, we’ve known that for a long time, but also accelerating.
The way this was originally found was by looking at very bright supernovae. These are the explosions of dying stars and these distant supernovae were seen to be fainter than anybody expected and one interpretation was that they’re accelerating away from us and at first it wasn’t clear what really was going on, but that is the consensus picture at this point that this… You have this acceleration driven by this powerful new… Well this is… it’s almost like an antigravity, so whereas dark matter makes up galaxies, it has a normal gravitational interaction, this other stuff has some kind of negative pressure. It pushes things apart and it could either be a new kind of energy density, a vacuum energy density or it could be telling us that our basic equations are wrong and we have to rethink everything, so this one has people very excited and puzzled and it’s not going to be answered you know this one will not be answerer tomorrow, but it’s a big one and it certainly affects the future evolution of the universe as well, so.
Question: Do you think that life will continue in the Universe indefinitely?
Katie Freese: Well with the dark energy most people do think that the universe itself will exist indefinitely, but the other question is whether or not there can be life in the long term future. In the standard explanation for the dark energy… I shouldn’t say standard because it really is a big puzzle, but if there is a vacuum energy that is constant in time it becomes more and more the driving force of this expansion and causing evermore acceleration. In that picture then life dies out because you’ve basically… It’s perhaps counter-intuitive, but as everything gets farther and farther apart you do have this floor to the temperature of the universe set by the vacuum energy. It’s a hocking temperature, so as you’re trying to operate closer and closer to this cutoff from this vacuum energy any kind of life form actually overheats, so as I said it is kind of counter-intuitive, but you just can’t… It’s something you can’t avoid. Now on the other hand what we wrote in our paper is we were saying well but if it is not a constant vacuum energy, if it either time changing so that it is decreasing into the future or that you have this kind of Cardassian Expansion that I was mentioning in either case then life could actually continue because you don’t have this floor in the temperature. In fact, instead it is also going down and so you can continue in clever ways to have life continue to exist. [00:27:42.08]
Question: Will life continue to exist as it does here on Earth?
Katie Freese: No, no, not at all. Yeah, something really very unpleasant from our point of view, so I have no idea, but certainly not people, not… Things will get very, very spread out and distant and cold and I’m talking about life in the sense of computation being able to continue.
if you think about our memories or our thoughts as a type of computation then is there some way you could have a molecular cloud, just like the kind I was talking about for the formation of stars where the different pieces of it communicate in some way and so you have intelligence of a completely different type than what we’re… than what we enjoy. So these bodies that we enjoy are not going to make it.
Question: How does the possible existence of other dimensions affect our study of the universe?
Katie Freese: I was mentioning this one possibility that we are living on a three dimensional surface, but that there are other dimensions out there. In string theory you would need ten dimensions and it’s possible… There is a number of different possibilities. One is that at every point in this room there is a tiny curled up dimension that we don’t know about because nothing that we… that we can’t go in there. It is too tiny and nothing we know about can fit in there either, maybe gravity can communicate through these additional curled up dimensions. That is one possibility. The other possibility is that one of the other dimensions or more of them could be large and cutoff at the other end by another brain similar to ours, so people wonder well what is the affect of the matter, is there some kind of dark matter on that other brain and that is actually what we’re seeing when we look at galaxies or is there when the accelerator at CERN, the LHC, when they’re taking data are they going to see missing energy that leaks out into the extra dimensions? This again would require the extra dimensions to be somewhat larger in order for that to happen, but it is certainly possible.
Another project that I worked on, this one was a lot of fun. If we’re living on a three dimensional surface like that and it is possible for some gravitational signal or I don’t know what kind of signal, something to leave our brain, go into the extra dimensions and then come back in the distant future and if the shapes are right, so imagine our brain is curved and the extra dimension… So I guess I’ll try to illustrate, so our brain is like this and in the extra dimensions you can cut it off by… You can do a shortcut path by cutting across then you could communicate information in a way that looks like it is faster than the speed of light, so that would be fun.
Question: How does one visualize these extra dimensions?
Katie Freese: It is a spacial… I am thinking in terms of spacial extra dimensions, so not time. Well there are some models where you have additional time dimensions, but what I’m talking about now you still have this single time dimension, but the… So we have here you know the… You move to the right. You move up. You move… The three dimensions that we’re used and probably you could just keep going on infinitely in any of those directions whereas the other dimensions I’m talking about like I said if they’re small then… So where I’m sitting right now I could move in the X direction. I could move forward. I could move in the Y direction. I could move to the right. I could move in the Z direction. I could move up, but I cannot move in this other direction because I’m too big, so these other directions are… They’re like curled up little circles and they’re just really tiny. That is one possibility.
Recorded May 7, 2010
Interviewed by David Hirschman
Katie Freese: I think people have the misconception that the big bang is the universe starting from a point. In fact, it is very different from that. Probably you know that the universe is expanding, so if we go backwards in time then you can watch the universe contract as you go backwards in time. So for example, if you took a tabletop then any two points would get closer together, but the points that are way far apart if you had… Let’s say it’s an infinite tabletop, so as these points get closer and closer together you still have a tabletop that is infinite in extent. It’s not like everything comes into one point, but eventually you reach such a high density. Things are so compact and right on top of each other that we lose our description. Physics fails. That is what the big bang is, so it’s actually we would need to have a theory of quantum mechanics and gravity simultaneously to be able to discuss physics going backwards in time any further, so it is really a high density situation that we call the big bang, but there is really no explosion. There is no bang. There is no singular point. But so yes, it does make sense to ask well what happens when you reach that density and that is what people are trying to do in theories of quantum gravity such as string theory or well some of the cosmology that I’ve done also is in the context of brains where our observable universe is living on a three dimensional surface in a higher dimensional universe and there could be other brains out there and how these brains intersect one another and their motions and so on has been… So there are different avenues to try to pushback our level of knowledge and they are very active, but very difficult.
Everything was more dense and then there is a certain point where… which we call the big bang and it’s from that point forward that we start our clocks, so that’s… And then so and we say the universe is 13.7 billion years old is relative to that very high density situation.
Question: What are black holes?
Katie Freese: Inside the Milky Way and every other galaxy there is a giant black hole at the center and it is hard to explain where these came from, but even more peculiar is the fact that already at early times there are billion solar mass black holes. These weigh a billion times as much as the sun and this it at a redshift of six. Redshift tells you how much more dense the universe was at that time and so you have to in very rapid fire do something from forming these first proto stellar objects collapsing them probably to make… Before my work people thought you made relatively small stars and how you’re going to grow those up to making million and billion solar mass black holes is a puzzle and so one of the contributions we made was to say hey, but we think that the first stars can be quite a bit larger and then it would make sense for the large black holes to be able to form.
We think that these black holes grow by accretion, but the accretion is in a disk, so it is a flat ring around the black hole, so the stuff is swirling around in the accretion disk and it is moving pretty rapidly and before it falls into the black hole it’s giving off radiation, so what you’re looking for is the radiation of this stuff that is falling into the black hole and from studying that in addition to what you’re already saying about the motions of other things around the black hole you can infer that the black hole should be there.
Question: What is dark matter, and how does it affect our picture of the Universe?
Katie Freese: the galaxy is and in fact, the universe as a whole have the… they’re made of different pieces and the atomic matter actually is only a very small portion, so the rest being the dark matter. In fact, it’s kind of… It’s revolutionary over the past decade that this had become clear that if you add up everything that we’re familiar with on a daily basis such as your body, the walls, the planets, all these things, all the atomic matter only adds up to 4% of the total content of the universe and the other breakdown is in terms of dark matter and dark energy and right we’re talking about the dark matter, which is the predominant bulk of the mass in the galaxies and clusters and so on, so when people study these first stars they were aware that they form inside these big globes of dark matter and at the center of this… of the dark matter you have a proto stellar cloud of hydrogen and helium that starts to collapse, so our contribution was to say well but what about that huge bulk of material that’s out there, doesn’t it play a role in this star formation process especially because these first stars are forming smack in the middle of these… These spherical regions are called halos, so these halos of dark matter, especially near the centers is where a lot… there is a huge amount of dark matter in there and that is where your star is forming, so what we think happens is that there is a kind of dark matter power basically.
The dark matter particles and the ones that we believe… There is a lot of experiments going on right now to try to detect these particles and I think that it is going to be resolved in the next five years, ten years at most and the most likely candidate they’re called WIMPs, which stands for weakly interacting massive particles and these WIMPs whenever there is two of them that find each other they interact among themselves and they actually annihilate, so they lose their original identity and they turn into something else, but in that annihilation process dumps a lot of heat into this proto stellar material, so you’ve got this proto-stellar cloud that is trying to collapse to make a small star, but all of the sudden you’re stopped because you have this heat source that stabilizes the cloud and prevents it from collapsing anymore, so and it is actually really a star. The nomenclature dark star could be a little misleading in the sense that people think well it is probably made of dark matter, but it really isn’t. It’s really made of hydrogen and helium and just a smattering of dark matter. It is a very powerful heat source and less than 1% of the mass is dark matter and the annihilation process gives a heat source that powers the star and it shines. Very bright objects, they really are stars, so they’re atomic objects that shine due to the dark matter power.
Question: Do you think the Universe has evolved in a logical way?
Katie Freese: Wow, I think if we try to write down a universe on a piece of paper that was the most simple and the most elegant there is a lot of things you wouldn’t find, so if all the way… all the details intermesh, are very important to for example, allowing people to exist and I mean on the biological level I guess this is obviously that we’re very dependent on respiratory system and all the rest of it, which is not something that you would just invent again if you had a random piece of paper and certainly what we’ve discovered, this sort of pie picture of the universe that you have 4% atoms, dark matter, which I think is the… That is a solvable problem. I think we’re on the edge of solving that one, but then all the sudden this dark energy appeared as a complete mystery. This was on the late 1990s, so I think I was saying around… In the past 10 years, around the turn of the millennium it’s really been the golden age for cosmology from the point of view of data coming in and really affecting our thinking, so this is a very bizarre, probably illogical thing from our current understanding of what powers the dark energy, so the thing that we see is that apparently the universe is not only expanding, we’ve known that for a long time, but also accelerating.
The way this was originally found was by looking at very bright supernovae. These are the explosions of dying stars and these distant supernovae were seen to be fainter than anybody expected and one interpretation was that they’re accelerating away from us and at first it wasn’t clear what really was going on, but that is the consensus picture at this point that this… You have this acceleration driven by this powerful new… Well this is… it’s almost like an antigravity, so whereas dark matter makes up galaxies, it has a normal gravitational interaction, this other stuff has some kind of negative pressure. It pushes things apart and it could either be a new kind of energy density, a vacuum energy density or it could be telling us that our basic equations are wrong and we have to rethink everything, so this one has people very excited and puzzled and it’s not going to be answered you know this one will not be answerer tomorrow, but it’s a big one and it certainly affects the future evolution of the universe as well, so.
Question: Do you think that life will continue in the Universe indefinitely?
Katie Freese: Well with the dark energy most people do think that the universe itself will exist indefinitely, but the other question is whether or not there can be life in the long term future. In the standard explanation for the dark energy… I shouldn’t say standard because it really is a big puzzle, but if there is a vacuum energy that is constant in time it becomes more and more the driving force of this expansion and causing evermore acceleration. In that picture then life dies out because you’ve basically… It’s perhaps counter-intuitive, but as everything gets farther and farther apart you do have this floor to the temperature of the universe set by the vacuum energy. It’s a hocking temperature, so as you’re trying to operate closer and closer to this cutoff from this vacuum energy any kind of life form actually overheats, so as I said it is kind of counter-intuitive, but you just can’t… It’s something you can’t avoid. Now on the other hand what we wrote in our paper is we were saying well but if it is not a constant vacuum energy, if it either time changing so that it is decreasing into the future or that you have this kind of Cardassian Expansion that I was mentioning in either case then life could actually continue because you don’t have this floor in the temperature. In fact, instead it is also going down and so you can continue in clever ways to have life continue to exist. [00:27:42.08]
Question: Will life continue to exist as it does here on Earth?
Katie Freese: No, no, not at all. Yeah, something really very unpleasant from our point of view, so I have no idea, but certainly not people, not… Things will get very, very spread out and distant and cold and I’m talking about life in the sense of computation being able to continue.
if you think about our memories or our thoughts as a type of computation then is there some way you could have a molecular cloud, just like the kind I was talking about for the formation of stars where the different pieces of it communicate in some way and so you have intelligence of a completely different type than what we’re… than what we enjoy. So these bodies that we enjoy are not going to make it.
Question: How does the possible existence of other dimensions affect our study of the universe?
Katie Freese: I was mentioning this one possibility that we are living on a three dimensional surface, but that there are other dimensions out there. In string theory you would need ten dimensions and it’s possible… There is a number of different possibilities. One is that at every point in this room there is a tiny curled up dimension that we don’t know about because nothing that we… that we can’t go in there. It is too tiny and nothing we know about can fit in there either, maybe gravity can communicate through these additional curled up dimensions. That is one possibility. The other possibility is that one of the other dimensions or more of them could be large and cutoff at the other end by another brain similar to ours, so people wonder well what is the affect of the matter, is there some kind of dark matter on that other brain and that is actually what we’re seeing when we look at galaxies or is there when the accelerator at CERN, the LHC, when they’re taking data are they going to see missing energy that leaks out into the extra dimensions? This again would require the extra dimensions to be somewhat larger in order for that to happen, but it is certainly possible.
Another project that I worked on, this one was a lot of fun. If we’re living on a three dimensional surface like that and it is possible for some gravitational signal or I don’t know what kind of signal, something to leave our brain, go into the extra dimensions and then come back in the distant future and if the shapes are right, so imagine our brain is curved and the extra dimension… So I guess I’ll try to illustrate, so our brain is like this and in the extra dimensions you can cut it off by… You can do a shortcut path by cutting across then you could communicate information in a way that looks like it is faster than the speed of light, so that would be fun.
Question: How does one visualize these extra dimensions?
Katie Freese: It is a spacial… I am thinking in terms of spacial extra dimensions, so not time. Well there are some models where you have additional time dimensions, but what I’m talking about now you still have this single time dimension, but the… So we have here you know the… You move to the right. You move up. You move… The three dimensions that we’re used and probably you could just keep going on infinitely in any of those directions whereas the other dimensions I’m talking about like I said if they’re small then… So where I’m sitting right now I could move in the X direction. I could move forward. I could move in the Y direction. I could move to the right. I could move in the Z direction. I could move up, but I cannot move in this other direction because I’m too big, so these other directions are… They’re like curled up little circles and they’re just really tiny. That is one possibility.
Recorded May 7, 2010
Interviewed by David Hirschman
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