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This is about science produced by the California Institute of Technology and originally broadcast by station KPP C. Pasadena California. The programs are made available to the station by national educational radio. This program is about the early universe with host Dr. Peter Letterman and his guest Dr. Robert Waggoner research fellow in physics. Here now is Dr. Leslie Mann. From the earliest antiquity man has gazed at the heavens and wondered how they fit into the human scheme of things. Perhaps if he was a religious man how they fitted into the divine scheme. Or if he was a more modest and perceptive individual how he fitted into the scheme of the universe what lay beyond our atmosphere and beyond our planets far in the voids of deep space. And what was the message of the stars. With his characteristic tenacity courage and imagination in the same spirit with which he has delved into the many minute
and mysterious interior of the atom so has manned probe outwards and onwards to the edges of the solar system to distances so great that by them measure our earth is a small as the constitutions of the molecule appear to us. He has asked and he has hypothesized and some answers have come shreds of information streaming in. In the romantic pale rays of the starlight or in the warm beams of the sun. But each answer has posed more questions pushing us back in time and on in space to the edges of the universe. I guess tonight a cosmologist an astrophysicist has recently made some deductions about old stars in our Milky Way which pose new and serious questions about our basic ideas of gravitation. Dr. Robert Wagner graduated from Cornell in engineering.
He then received his Ph.D. in physics from Stanford and he is currently a research fellow at the California Institute of Technology working in the fields of relativistic astrophysics and cosmology. Bob I'd like to start off by talking a little bit about the history of the studies of the universe. Well you said Peter Man has always been interested in looking toward the heavens to discover exactly what's out there and how he fit into this whole scheme. As time went on he looked further and further out first discovering that he was a member of the solar system contain the sun and the other planets as time went on he certainly he soon realized however that the sun was only one of many many stars hundreds of billions of stars in our own galaxy. And then of the Galaxy was only one of uncountable galaxies in the universe as far as we see. We see galaxies out there. We have not come to the end of our search.
And so my remarks about the edge of the universe are really completely meaningless. That's right. As far as we know we have not reached the edge of the universe present time but our understanding of the universe come a long way especially since Einstein's theory was developed in and around one thousand sixteen. Give us a mathematical basis for understanding the universe. And so this is a rational mathematical basis that Einstein gave us I suppose gave us some means of going backwards and forwards in time in our knowledge of the universe. Yes that's right. We have expanded our horizons outwards. But what I'm going to talk about today is expanding our horizon backward in time discovering what the universe was like in the far distant past. Well before we go too far back in time Bob. What do we know about the universe as it is actually today. Well Peter one of the most important facts we have today is that the universe is expanding. We know what expanding because the
light that we receive from atoms in distant galaxies appears to be shifted in frequency shifted hostile to so Shorter's frequencies I should say. Like a train which is traveling away from you. Sound waves in which are shifted to longer wavelengths. So the pitch goes down if this train recedes from you. So in fact we know about our universe that everything is flying awkward sudden enormous rate. That's right and we also know approximately the value of this rate today. Another fact we know the present amount of visible matter at least in the universe. It's mostly in the form of hydrogen atoms the density of this matter. It's smoothed out form a collecting its concentration in galaxies the proximately one atom in a cubic yard which isn't very much at all. Also we know recently we've discovered that there is a low very low temperature radiation streaming in from the edges of the universe seems to be streaming in with equal
intensity in all directions which indicates that it's not coming from the sun or even from our own galaxy. Coming from the entire universe itself. In other words we feel that we are in the middle of something which extends in much the same way in all directions as far as one can possibly imagine. That's right these measurements are becoming very accurate now. If this radiation is equal in all directions to less than 1 percent. And so this means that in general. Whatever is beyond us there is the same sort of thing beyond us in all directions. That's right. What other things Bob can we learn about the this remarkably low density and this radiation uniform radiation that we observe on Earth. Well there's some disagreement among cosmologists today these observations do indicate some things about the universe or they don't prove them. Firstly it seems the universe has expanded from a state of very high
temperature and density higher than we can imagine today. I think conceivably you could have expanded from a state of effectively infinite temperature and density. Another way. It's of course once a tiny concentrated spot with enormous energy. Well you can think of it that way although the universe does not have any really boundary in the sense that we think of a star having a boundary you can still think of its density being extremely high. This is the so-called big bang universe as first envisioned by a Belgian Abbey George le Metra in the early part of this century. He described this early phase of the universe as the primeval atom from which everything was born. Do you find this incident at any variance to his religious convictions or don't we know anything about that. Well I don't know anything about that. He is in fact he's still active today I believe. Oh or at least he was active a few
years ago. Well we also know from these observations we have strong reason to believe at this early phase of the universe was exceedingly homogeneous and by that very uniform you mean everything was the same and well I reckons everything we could measure we could have measured would have been the same at all points at a given time. But everything was changing with time. The galaxies presumably formed much later as the universe cooled down into its expansion. But in this early phase it was. It seems that it must have been very homogeneous at least. We like to believe this from the observation God we have this weird galaxy used so much particularly being so close to Hollywood where it has a quite different meaning from its proper meaning. How would you define a galaxy as an astrophysicist. Well the galaxy is an aggregate of stars and gas made up of something like a hundred
billion stars. And it seems to be the fundamental building blocks of the universe. It's the smallest aggregate of matter which partakes in the universal expansion of the universe. So when this sentence seems to be something fundamental so and what you're saying is that the universe started without any of these groupings. But in everything was much the same and that the groupings the galaxies were created later. That's what most cosmologists believe today. There are some other ideas for the formation such as they also began in little explosions not condensing but instead exploding. When we see them today. So that gives us some idea about our knowledge of the universe today. But Bob what we are really talking about now is what was the universe like in the past. Yes that's been my field of interest the last few years and I'd like to describe in general what we think went on during its expansion of the universe.
I could take it back to a time when the temperature was something like 100 billion degrees and the density of ordinary matter was of the order of the density of water. However during this time the density of radiation will be even higher than many many orders of magnitude higher. So it was like a huge fireball gaining a lot of radiation not much matter. When you speak about radiation Bob how would you describe that to me. To the layman. Well it's ordinary electromagnetic radiation. You can think of it as photons in a particle sense and depending on its frequency you can think of it as radio waves light waves. I see so all these forms of which the familiar ones of the man in the street are radio waves and like waves and possibly heat waves. I trade with these ways with much higher energy at this early time and as the universe expanded which we believe was the case both the density and temperature decrease due to this expansion until the
temperature reaches about a billion degrees. Which happens about 100 seconds after the initial stage talking about. Then we can begin to fuse the nuclei together really fusing the initial neutrons and protons together to form a more complicated nuclear fusion can be accomplished because of a very high velocity. These particles this temperature how they can actually stick together and not the. Reason that they stick together is this is this due to the fact that they are traveling at very high speeds Bob and they simply strike each other and remain stuck together. That is probably much too mechanical point of view. Well they're sticking together involves many complications from nuclear physics. The reason they can stick together is for those times that there are some so much radiation around it. They tend to break up these particles and they try to stick together so the radiation intensity must decrease before we can begin building a nuclear
which we observe today. And yet as you point out we have a very high density mass we have very heavy volume of some sort which which contains many many many particles very closely packed and yet none of them are sticking together until a certain time has elapsed after the initial instance why because they're so hard they just cannot stick together. However as the temperature cools I say eventually they reach the point where they can. However they're still not in the form in which we're used to seeing man because there are still electrons which are free. And it may also be even neutrinos around this time. So it's a very complicated situation with many different kinds of particles but maybe I should ask you briefly for a few words about electrons and neutrinos for that matter. Well the electron is the ordinary particle we so she has been traveling around the
nucleus and the atom. It's much lighter than the nucleus but has a charge opposite in magnitude similar to that of the nucleus. There are strong of course is most familiar I guess to ordinary people as the carrier of the electric current. That's right. The ordinary thing. So she's electric current you know. Whereas the neutrino is quite different. It has no man like electron has no charge. The only thing it has is a spin. The neutrino is spinning in certain direction relative to its line of flight. Or is it anti particle. The spins in the opposite direction is the only difference between these particles that you know that very weakly with other particles. That's why they are very difficult to detect today. So we don't know too much about how important they are in the universe today. They could be very important. We'll see in a while. Now if the temperature drops eventually at about 10000 degrees
heat electrons can combine with nuclei to form atoms. Soon after that we believe the galaxies can dance leaving the universe and state we see it today where the temperature of this radiation is a few degrees. When you say you can do this do you mean that they actually form solid. What we would refer to as solid matter BB. No they remain in the gaseous state and eventually form stars and planets. This expansion phase I described has taken about 10 billion years we believe. But certain strict certain features of this general picture I described are still unclear exactly how much ordinary matter. How many neutrinos are present and what was the expansion rate. I think we know the expansion made today but we're not sure what it was back in the past.
In other words we know how fast we are all flying apart and coming unglued at the moment but we are uncertain whether in in the years gone by whether this was happening at a higher or lower rate. That's right and we're pretty sure what's happening in a higher way but we're not at all sure how much faster now how could we learn more about this process. Well recently the method I'm going to talk about has become increasingly important. Learning about conditions in the early universe. And what do you do in this method is to compare the element production during a fairly fate of the universe. We have the elements we have today. In other words try out different models of the universe and discover its the elements they produce and give what we observe today. This type of investigation was began about 20 years ago by George dam and maybe pursued by many people. The work I'm going to describe was carried on with Dr.
Fowler your Caltech Dr. Hoyt Cambridge University in England I see. And so when we observe then that there are many different ideas about the universe. Most of them which start with a big bang. But I expect Bob that there must be some particular big bang universe which is generally accepted to be the most likely one. Yes that's right there is one model which is the most popular possibly because it's the simplest or philosophically the most pleasing. This was the model which came out studied and most other people. And is that that is that is the model in which you have studied in which you are suggesting may possibly not be correct is this true. Well depends on the observation. We very well could be that it's not true have to. What are the basic assumptions about this so-called popular model. Well first of all we'd like to assume that Einstein is correct in his theory of gravitation
correctly described the large scale dynamics of this expanding universe. I would also like to believe the observation seemed to indicate at least during the recent past that the universe would look the same in all directions as we look out from any point and it would look the same and also we'd like to believe that neutrino density the number of neutrinos is not much greater than the radiation density in the world it doesn't dominate the universe. Under these assumptions we can calculate exactly which nuclei were produced during this epoch I described in the past about a billion degrees. In other words Bob you make this assumption the basic ideas about gravitation and things are the same in all directions. And then using the known laws of physics. You were caught how these elementary particles would combine to form the different elements which we are going to
observe today on Earth and strain on the production of very sensitive to the various factors I've considered. Solar provides a good test of whether the model is correct. Now what sort of elements are produced by. Well actually not very many. Only the very lightest elements are produced hydrogen helium and lithium and not very much lithium at all and not very much healing in fact only about 1 in 10 atoms produced are helium. The rest are mostly hydrogen. Very very little if so it appears that most of the heavy elements we have which we observe every day will produce you no other way. Such is commonly believed within stars which subsequently exploded and dispersed their contents throughout our galaxy. You know there were only interested in light elements. I see as the light elements that are important and the heavy elements came later on in the history of the universe. That's what we believe in present. But now there's another complication which
arises when we want to compare these predictions with the observation. And that's just what I mentioned that most of the material we see today has been contaminated by other process such as stellar synthesis. So the interpretation of the observations is unclear. However recently certain observers have noted that all very All Stars in the halo of our galaxy is very far away from the main part of our galaxy appear to be deficient in helium. Remember it's only their atmospheres are deficient which are deficient in human because the only part of the star we can see. Indeed their atmospheres might have been deficient in helium because the healing might have settled down in the atmosphere and lighter hydrogen being on top would be the only element we would see. However there appear to be other heavier elements in the atmosphere so it's not clear whether they really are sampled. The primeval material out of which the galaxy condense.
Bob how do you know that these are very old style. Well it's a long chain of reasoning. Having to do with the way they evolved and the way they appear today we can make certain adduction is knowing a man and a woman are sitting about actually how old they are. This involves theoretical considerations of stellar evolution. In other words you can date these stars and as you point out on some of the older ones seem to have less and less of a certain substance than you might have expected them to have less rain less helium than what most of the other stars we observe and I guess in fact much less helium but a factor of 100 lower than ordinary stars. Now if this helium really was low in the primeval material of which the galaxy can dance then we can draw some fairly strong conclusions such as the fact that either Einstein's theory of gravitation is wrong or
the universe appeared much different in different directions in the past what we call an isotropic universe or on known kinds of particles were present during its early epoch or most of the mass in the universe is in the form of neutrino and not in the form of ordinary matter is we think about it. So we would not now like to look at other models of the universe he said. So we see BB that then because we find there's just too little helium in these old stars that something something doesn't fit in something must be wrong either Einstein's theory is wrong or the universe isn't universally homogeneously constituted or as you say some unknown particles were present or there are just many more neutrinos and we expect there to be but then as you say what
about thinking of some other hypothesis what about other types of Big Bang universes. Well I've recently looked into other possibilities within its framework for modifying the universe. One factor we can alter is the expansion me the early times. You mean we can assume that the expansion rate is is a different value from what we've used in our previous calculations. That's why we've used Einstein's theory to give us the expansion rate. But we could let the rate be either faster or slower according to what the theory says. In other words then we assume that the world is the universe is flying apart at a different rate now what happens Bob if you were to assume either that we were flying apart more slowly than we thought we were. Or that we were falling apart faster than we we think we are which often seems to be the case with individuals. Well curiously enough either possibility will lead to much less production of feeling agreement with these observations. If we interpret them
the way I indicated the reason why the low expansion rates give you low here in the neutrons all that came before you can form him in a meeting why the fast expansion rate very little helium if there isn't time I think to form him. So for two quite different reasons we can attain a low helium production in these early universe. So we have the interesting result then that maybe the expansion rate of the universe is not what we thought it was. That our information at the moment tells us that it could be either faster or slower and we cannot judge from that criterion alone. That's right we could look at some of the yellow or other light elements which are produced. Such a universe in order to judge further the correct model. But there's another possibility. Which we might consider and that is that the universe is filled with a very dense sea of neutrinos which we couldn't detect because as I indicated before they interact very
weakly with other particles and these neutrinos directly alter the nuclear reactions which form the elements. For instance if we had initially very many neutrinos we would also have very few protests very few neutrons initially and this would lower the hearing in production. We had very many anti neutrinos it would produce an essentially pure neutron universe which can produce both high helium and somewhat lower helium depending upon the details of the model. But again we produce no heavy elements in any of these types of universes. Which again argues strongly for the fact that ordinary processes in stars as we believe them to be taking place today have produced most of the heavy elements we observe in other words part we feel that our present explanation and using our present physics we can account for most of what must have gone our stars. Yes there are many details but it seems to be a plausible hypothesis.
How could we finally decide on whether this was or was not correct. Well in principle we can by looking at the abundance of these light nuclei hydrogen helium and lithium and their various isotopes. These observations are very difficult because as I indicated humans look at contaminated material as material in its primeval form and have not been dirtied up by other processes which have occurred in our galaxy. So at present the only good observations we have and they are not very far in determining this are the helium observations but in the future we hope to obtain observations of deuterium which is an isotope of hydrogen. Its nucleus contains a neutron beside a proton and lithium. In order to determine exactly which one of these models might possibly be right. But keep on talking about observations and yet I guess we've never really defined how we
make these observations how or how in fact do you make these measurements on these distant stars where you look at the spectra of the light coming from the atmosphere. You see these narrow lines which indicate the various elements in your atmosphere and by. Knowing the strength of these lines and knowing something about the atmosphere of the stars we can determine how much of that element is present in the atmosphere that star and atmosphere presumably is composed and material out of which that star condensed which in the case of the All Stars is in fact the primeval material that we're interested in. So we must obtain observations of the very oldest stars in our galaxy. You do have hopefully a sample of this primeval material and so I know that this is a ridiculous question to ask a cosmologist Bob but how briefly could you summarize the sort of work and the ideas and the directions in which your
work is leading. Well Peter we've seen that there are strong reasons for believing that the universe has emerged from an incredibly hot and dense condition. I try to show how a knowledge of the composition of the remnants of this explosion can help us understand more about how the universe developed in the past and what it is like today. And so we see how modern developments in astrophysics are giving us new insights in our universe. How it was formed what its early history was and possibly even where it is going. And we have seen how the cosmologists constructs his theory of the universe and the fabric of observation and imagination of reason. Experiment and wild guesses and how he tests his hypothesis against a constantly increasing supply of information and data and rejects that which does not stand the acid test of reason and forms a stronger and a firmer base from which to launch his
newest wild guess. Thank you Bob. This was about science with host Dr Peter Letterman and his guest Dr. Robert Waggoner. Join us again for our next program on Dr. Albert hippies who will lead a discussion about the oldest mountain range about science is produced by the California Institute of Technology and is originally broadcast by station KPCC Pasadena California. The programs are made available to the station by national educational radio. This is the national educational radio network.
About science
About the early universe
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California Institute of Technology
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University of Maryland (College Park, Maryland)
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This program focuses on scientific study of the early universe. The guest for this program is Robert Wagoner.
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Interview series on variety of science-related subjects, produced by the California Institute of Technology. Features three Cal Tech faculty members: Dr. Peter Lissaman, Dr. Albert R. Hibbs, and Dr. Robert Meghreblian.
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Guest: Wagoner, Robert V.
Host: Hibbs, Albert R.
Producing Organization: California Institute of Technology
Producing Organization: KPPC
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University of Maryland
Identifier: 66-40-41 (National Association of Educational Broadcasters)
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Duration: 00:28:48
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