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SPEAKER: Thank you so much for coming, everyone. So this is our final lecture in the series of Bethe Lectures, so I'll tell you a little bit about Hans Bethe, who this lecture series is in honor of. And then I will introduce our speaker. So Hans Bethe began his career in 1920 studying mostly quantum physics. At some point, late in the 1920s, he actually left Germany to escape persecution for his Jewish heritage and moved to the UK.
And in the UK is where he began his career in what would be a very, very long career in nuclear physics. And he did many things over the years in nuclear physics. He also wrote a comprehensive review of what we would now call solid state physics. He received a Nobel Prize in 1967 for his work on the energy production in stars, particularly burning hydrogen to helium and the CNO cycle, and he was at Cornell starting in 1935. So that's why we're very honored to have him as part of our department here.
One of the other things that I was excited about when I read about what he studied over the years was that he came up with a waveguide directional coupler called the beta hole coupler. So he has worked in many, many different areas of physics and really had an extremely long career, 80 years of being a physicist basically, and created an amazing department culture here at Cornell that I think that we have today, a beautiful culture in our physics department here.
He was also an advocate, so he was an early opponent of development of the hydrogen bomb. He was an advocate for the limited test ban treaty, and he was a proponent of peaceful applications of nuclear energy. So we have this series to honor him and also bring wonderful physicists and humans here to talk to us. So now, I will introduce our speaker for today.
So our speaker is Professor Wendy Freedman from the University of Chicago, and she's one of nine named professors at the University of Chicago. So she's the John and Mary Sullivan University Professor of Astronomy and Astrophysics in the college. She's been at the University of Chicago, I believe, since 2014, and before that, she was a PhD student at the University of Toronto. After that, she then moved to Carnegie Observatories, where she was a Carnegie fellow and then became [INAUDIBLE] founding chair of the Board of Directors of the Giant Magellan Telescope.
She is the recipient of many, many awards. She's an elected member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society. She's an elected fellow of the American Academy of Arts and Science, the American Physical Society, and a Legacy Fellow of the American Astronomical Society. She also has many, many awards. I'll read some of them. [LAUGHS]
So her awards include the Marc Aaronson Lectureship and prize, the McGovern Award for her work on cosmology. And she also was a corecipient of the Gruber Prize for Cosmology in 2009, which is a very prestigious prize in our field. So we're very lucky to have her here today to tell us about observational cosmology and some of her work. So I would love it if we could welcome her.
[APPLAUSE]
WENDY FREEDMAN: Thank you very much for that introduction. Can you hear me OK? Great. It's a pleasure to be here today. And it's a real honor to be giving the Bethe Lectures. I think Bethe was one of the most distinguished physicists of the last century and maybe of all time. He was a phenomenal physicist. So it is a real honor and a pleasure to be here. I will speak this evening about recent results in observational cosmology and answer the question of how fast the universe is expanding and tell you about our measurements to do that.
It's a quantity called the Hubble constant. And I'll tell you about some of the people that enabled measurements of the Hubble constant and the discovery of the expansion of the universe early s and then tell you about the science but also about the facilities that have allowed us to make these measurements and beginning with telescopes at Mount Wilson and Pasadena, California where Edwin Hubble made his first discoveries, then successive generation of telescopes on the ground, and culminating in the 1990s with the launch of the Hubble Space Telescope that allowed us to get above the Earth atmosphere.
Most recently, the launch of the James Webb Space Telescope, which you may be familiar with which was launched last Christmas, and I've been very fortunate to get data from the telescope in its first cycle. And then to tell you a little bit about the future and a telescope called the Giant Magellan Telescope which I have spent some time leading that project during the last decade. And it's scheduled for completion in the 2030s.
And so let me begin by introducing you to George Ellery Hale who was a solar astronomer. And he's a person who discovered that the sun has a magnetic field. And he was born in Chicago and interested in building telescopes. And he-- no. Good. He had a saying that came from the architect Daniel Burnham.
And he read-- this was in the Chicago Record Herald in 1910. And Daniel Burnham was fond of saying, "make no little plans." And went on to say, "they have no magic to stir men's--" and it was just men's but-- "blood" at that time. "Make big plans, aim high, and hope and work." And he went on to say that if you made little plans, they would be forgotten. But if you made big plans, they would last for longer than your lifetime. And George Ellery Hale really took that to heart.
And he built successively four of the world's largest telescopes at the time, which is a pretty phenomenal record. Need to apparently push this twice. OK, so he went out to Pasadena, California from Chicago in 1903. Brought his family out. At that time, Pasadena had dirt roads and really not very large population. And it wasn't much of a academic center. He was about to change that.
This is George Ellery Hale at Mount Wilson, looking out over the Basin in Los Angeles. And what he realized was that this was a phenomenal astronomical site. And it would remain one of the best sites in the world, even today, if it weren't for the lights of Los Angeles. So there's an inversion layer of clouds that it's very steady above that inversion layer of the atmosphere so that you get very high resolution through your telescope optics that you don't get a lot of blurring in the way you do at other astronomical sites.
So he brought his family out. There are actually letters from his wife, Evelina, that as he was building these telescopes at Mount Wilson and Palomar and there were a lot of technical problems and challenges and the mirrors didn't work right away and there were cracks and bubbles and all sorts of difficulties, and she says at one point, "I wish that damn mirror would just sink in the ocean."
Fortunately for astronomy, eventually, he really succeeded phenomenally and went on-- so one of the other things that he read in the newspaper in Chicago before he left for Pasadena was about Andrew Carnegie, who of course, had made his money with steel. And Andrew Carnegie had donated $10 million in 1902 with the idea, went to the Carnegie Institution, that he wanted to encourage investigation research and discovery in the broadest and most liberal manner and the application of knowledge to the improvement of mankind. And that really perked up George Ellery Hale.
So here is George Ellery Hale standing with Andrew Carnegie. And I'm told that this is one of the few pictures where you see that George Ellery Hale is actually taller than Carnegie. Carnegie was very self-conscious about his height. So apparently Hale would either be downhill or bending his knees in the picture so that he wouldn't offend Andrew Carnegie. But I guess this wasn't enough then to put Andrew Carnegie off and he funded the 60 inch telescope at Mount Wilson. So Hale himself was a solar astronomer, as I mentioned. So he built a solar telescope at Mount Wilson then went on to build 60 inch. And before the 60 inch was completed, he already was trying to raise money to build the 100 inch telescope at Mount Wilson.
And as we'll see in a moment, these two telescopes, each of them in their own right, really changed our perception of the universe. And then he wasn't done. He convinced the Rockefeller Foundation to fund the building of the 200 inch telescope at Mount Palomar. And then continuing on with his legacy eventually, telescopes, because of the lights in Los Angeles, building larger telescopes there was not the thing that you want to do because faint objects can't be seen in Los Angeles anymore. So the Carnegie Institution moved its telescopes, or its new telescopes, Magellan telescopes, they're two 6 and 1/2 meter telescopes also built by the Carnegie Institution. So really continuing the legacy of George Ellery Hale.
So the 60 inch telescope was one of the first telescopes he had built at Mount Wilson, Harlow Shapley, who went on to become the director of the Harvard College Observatory, was at Carnegie at the time and he was interested in studying the distribution of objects that are known as globular clusters. So these are clusters of stars that there might be 100,000, or maybe even a million of these stars, held together by gravity. They have a spherical distribution.
And he was interested to ask a question of how are they distributed within the Milky Way galaxy? And this was in the 19-teens. At that time, we didn't know whether the Milky Way Galaxy was the entire extent of the universe or whether there were other universes, galaxies, like our own Milky Way and that the universe had a much larger extent.
And so he set out to see where-- so these dots here represent the positions of the globular clusters in the Milky Way. And he expected that he would find that the sun would be at the center of the Milky Way Galaxy, or the universe. And so we knew from the time of Copernicus, that the Earth was no longer the center of the universe.
Before that time, of course, people had thought that the sun revolved around the Earth with all the other planets. And Copernicus had told us that, no, the sun is the center of the universe. And so the expectation was, well, we'll find the sun at the center of the Milky Way. And instead what he found was that the sun is about 2/3 of the way out in a disk of this Milky Way and not the center of the universe anymore. So it really was a phenomenal discovery that came out of the 60 inch telescope.
And then with the construction of the 100 inch telescope-- they don't like me-- here we go. The astronomer, Edwin Hubble, after whom the Hubble Space Telescope is named, began to study objects that were known at the time as nebulae. Nebula is just a Latin word that means fuzzy.
And these objects had been known, since the 1700s, and as people started to take photographic plates, it could go fainter than the human eye, lots of these fuzzy objects had shown up, many of which were cataloged by a French astronomer named Messier. And Messier was interested in studying comets. So there are a lot of objects that have "M" And then a number after them in Messier's catalog. And all of the nebulae he discarded is uninteresting because they weren't comets.
But they turned out to be very interesting, many of these objects are what Edwin Hubble began to study at the 100 inch telescope. And what he was doing, there we go, was studying-- these are glass photographic plates, so this was the detector at the time. And what's shown here is the Andromeda Galaxy, which some of you may be familiar with. This is a negative image in this case.
So the stars are dark and the white part here, these are dust lanes that are caused by dust that is formed in the atmosphere of stars. And then when the stars die, this dust goes into the medium between stars, the interstellar medium, and it actually blocks the light that's coming to us from the stars we're trying to measure. And then you have to correct for that if you're going to make an accurate measurement of how far away the galaxy is from us.
And so what Hubble has marked here is-- you can see this in, which is crossed out. There's an object here that he's interested in. He writes "VAR!". So this is 100 years ago, this is 1923. So we're celebrating the Centennial of this discovery this year. And so why was he so excited about this VAR?
And it turns out that this object, which I'm sure you can't see very well, especially from the back, is a star in this nebula. It's known as a Cepheid variable. And these are stars that allow us to measure the distances of objects from us. And I'll describe in a moment, this was a discovery made by an astronomer by the name of Henrietta Leavitt in 1908. And Hubble now realizes looking at this plate, oh my goodness, this is a Cepheid. He can measure the distance to the Andromeda galaxy.
And when he does that, he discovers this is way outside the Milky Way. This is a galaxy in its own right, just similar to the Milky Way. And has now increase the size of our universe quite considerably. Interesting side story to this is that the Harlow Shapley who discovered that the sun is not at the center of our galaxy, he was also working with photographic plates.
And in the construction of these telescopes, in 60 inch anyways, they didn't yet have vehicles that could go up to Mount Wilson. And they used mule trains. And one of the drivers of the mule trains was a man named Milton Humason. And he went on to become one of the janitors at Mount Wilson once the 60 inch was completed. And then people there started to realize this guy was actually really very smart.
He only had an eighth grade education, but he was really interested in astronomy. So he began to work with Shapley and Hubble and others. And as Alan Sandridge, who was a well-known astronomer in the last half of the 20th century told the story, that Milton Humason, he was given the responsibility of actually developing these plates for many of the astronomers. So he walked into Shapley's office one day and he had noticed that there were stars that were on some plates and they had different brightnesses at different times.
So he went in and said, look Dr. Shapley, these look like they might be Cephied variables. And Shapley, who had then just measured the distribution of globular clusters in the Milky Way, had measured that the Milky Way was quite large. Turned out there was an error in the calibration, it also affected Hubble eventually. But he was quite convinced that the Milky Way was so large that it was ridiculous to think that there were Cepheid's in Andromeda. And he was annoyed. So he took his handkerchief, this is the back of the photographic plate not the emulsion where Humason had written, and he erased them.
So he missed the opportunity to make the discovery of both, the extent of the Milky Way, the existence of other galaxies and the expansion of the universe. It's just one of those stories where you never know. So you should believe it if somebody comes into your office and tells you something that might be interesting. Don't brush it off. So here's Hubble, the man Hubble, the telescope and this is the Mount Wilson 100 inch telescope.
And so what Hubble did was first he identified that there were galaxies outside the Milky Way. And then, as if that weren't enough, he went on to discover that if you measured how fast galaxies were moving, their velocities, and you plotted that against the distance to the galaxy, which he could now do with these Cepheid variables, there was a direct correlation between velocity and distance. And that correlation, the slope of that correlation, is what tells us how fast the universe is expanding. And that's what he was able to do.
So here's his discovery plot. This is this velocity increasing up and the distance to the right. So the farther away a galaxy is, the faster it's moving in velocity. So we like to tease our students to see whether they can recognize the mistake here because they would lose points on an exam if they plotted the axes the way Hubble did. This is a publication from the National Academy of Sciences in 1929. And if you notice, he has velocity in kilometers rather than kilometers per second. Didn't get caught by anybody, no editor. Now I have to press it five times. What is happening? Here we go.
So in 1915, Albert Einstein had published his general theory of relativity, which is a theory that describes gravity. And Einstein had realized that within his equations of general relativity, that the universe either was going to expand or it was going to contract. He could see this, his equations were actually telling him this. But there was no evidence.
And he did talk to astronomers of the day that the universe was expanding, we didn't know of galaxies yet. Hubble hadn't made his discovery. And there was no evidence that stars that astronomers have been viewing for centuries that there was any expansion of universe. So he added a term into his equations to force the universe to be static, not to move because he knew that the universe would have to be in motion.
It turned out adding this term, which can be called the cosmological constant, is a discovery that was made in the late 1990s, turned out to be right after all, but Einstein didn't know about this at the time. And when Hubble made his discovery, Einstein is reputed to have said, "this was his biggest blunder" because he could have predicted the expansion and he didn't. He added in this cosmological constant. So not many scientists, not many people, have their biggest blunder turn out to be one of their biggest discoveries. But that was Einstein. So here he is on this, it's called the catwalk, on the outside of the Dome of 100 inch telescope. And this is Edwin Hubble.
So he came to see-- came to Pasadena to see and discuss with people what the evidence was for an expanding universe. This is 1931. And so here is Hubble, he Apparently observed with a pipe and letting Einstein look through the telescope at Mount Wilson. So I like to tell students that Hubble had very important observers for him who could do his work for him.
So this is Henrietta Leavitt, who I mentioned a moment ago, who discovered that the stars, these Cepheid variables, if you plotted how bright they were compared to how fast they were changing in their brightness, what she discovered was that these stars, they have periods of variability from a couple of days to a couple of months generally. And it turns out that the outer atmospheres of the stars are actually in motion, they're pulsating. And they do this in a very regular way, such that the larger, more luminous stars takes more time for the atmosphere to go through its pulsation cycle.
And so the larger stars take longer, they're brighter, and they have longer periods. And that discovery is what allowed astronomers like Edwin Hubble to measure for the first time the distances to these galaxies. And before that time, of course, you look on the sky and you see in two dimensions, but you don't know is a star far away because it looks faint or is it intrinsically faint and you don't have that third dimension. And her discovery is what allowed astronomers for the first time to measure that third dimension, the distance of objects from us. And she really has not gotten very much credit for it.
Everybody knows the Hubble Space Telescope, there's a Hubble constant, there's a Hubble law, there's Hubble galaxies, there's lots of Hubble, Hubble, Hubble. We now refer to the period luminosity relation that she discovered as the Leavitt Law. And there's a biography that's being written of her now. So I think more people will come to know her story, but she kind of got relegated to the dustbin of history, which is kind of unfortunate, but I think that's changing.
So when we came to do the project with the Hubble Space Telescope, beginning in the 1990s, what Hubble had measured, so when you measure the slope of his correlation, that's what gives you a measure of how fast the universe is expanding today, it turned out that there were a lot of difficulties in making that measurement accurately. One of them is the dust that I mentioned.
So the dust, the dust grains that are between us and the Cepheid's scatters the radiation or absorbs the radiation that's coming from the Cepheid. And so it makes the star always look fainter, never brighter. It's in the way and it's blocking the light. And if you don't realize that it's there, the star looks fainter so you think it's farther away.
And you get the distance wrong. So that was one of the difficulties that Hubble had. The other is that when you're observing distant objects, so allowing us to get above the Earth's atmosphere using the Hubble Space Telescope was what allowed us to make much more accurate observations than had been possible before then.
And up to that time, people had been arguing about the expansion rate at a level of a factor of 2. And the expansion rate, if you know how fast the universe is expanding now, then you can extrapolate backwards, either think of it as a movie playing in reverse if it's been expanding at a certain rate and you play it backwards, how long has it been expanding for? Or Alternatively, you can use Einstein's equations for general relativity and integrate and determine the age of the universe.
So when we didn't know the age to better than a factor of 2, people argued about whether the universe was 10 billion years old or 20 billion years old. So that's kind of a big difference, it wasn't very satisfactory. And it was Hubble that allowed us to get above the Earth's atmosphere and make those measurements more accurately. More recently, there's been a telescope that is observing at mid-infrared wavelengths, very long wavelengths where the dust is negligible and we are also able to use that to improve our measurements of the Hubble constant.
So what we're doing is essentially creating a distance ladder where we measure these Cepheid variables nearby where we can get very accurate observations and then we tie into other methods. And one of the ones that we use is a very bright explosion called a supernova, and in particular, a so-called [INAUDIBLE] out to very great distances.
And one of the reasons we need to go out far, farther than we can do with stars like Cepheid's is that galaxies tend to congregate in groups, they like neighbors, they're people, they tend to like to be around other people. And when they're nearby, they interact via gravity and so they induce motions in their neighbors. So if you're trying to measure the expansion velocity and you get this noise on top of the expansion of velocity itself, that limits the accuracy with which you can make the measurement.
So we try and go out as far as we can so that the peculiar velocity so-called, that are induced by these gravitational interactions are small compared to the Hubble velocity, which is larger as we saw at greater distances. So the challenge now in measuring the Hubble constant, this is now the Hubble constant here shown as a function of the year in which the measurement was made.
So this is going all the way back to Hubble here. And he first got a measurement of 500. That was revised in the 1950s, went down to about 250. And then it went through this period where a few decades, and it wasn't possible to resolve that until we had the Hubble Space Telescope.
Now this is just a blowup going from about 1965 to 1990. And this is where this factor of 2 that had been really a thorny problem for a few decades that people were publishing values between these two, 50 and 100, and there was really no way to resolve that. And we didn't know the age of the universe to better than a factor of 2.
So these red lines are showing where we are today, and I'll describe in a moment that when we make measurements using the Cepheid variables, the way we did-- Hubble did, the way that we did for the key project with Hubble, we get a value of about 73. And in the last couple of decades, it's become possible to estimate the expansion rate in a very different way, making use of the background radiation from the Big Bang.
So there was this colossal Big Bang about 13.8 billion years ago. Universe has been expanding since that time and cooling. And in the early universe, the radiation that was coming from the Big Bang was blocked because of scattering by electrons in the early universe. And then when the universe cooled enough that you could form hydrogen atoms, so the electrons and protons combined.
And then we get to see the radiation from the Big Bang. And we can now make really precise measurements of that radiation. And when you do that, you get a value more like 67. So there's this new discrepancy between 73 coming from Cepheid's and 67 coming from the Big Bang and the measurements of the radiation from the Big Bang.
So in not only is there a difference, but if these measurements are telling us what now appears to be a real possibility that the uncertainty in the measurements is reflected now by the width of the bar shown here. And so that it's a really statistically significant difference.
And if that's true, it's telling us that there's something very fundamental that we don't understand yet about the universe, that when we make these measurements at high redshifts at early times, there was something different that telling us that there was something different at that early time. So here's the Hubble Space Telescope. What we began in the 1990s was a program to measure a number of galaxies so that we could get around this factor of 2 uncertainty and our goal was to measure the Hubble constant to 10%.
So that's the original Hubble diagram that I showed you earlier. And those observations fit into the first tick mark of what we can do today. So we can go much farther out. Now I mentioned, we still use Cepheid variables. And the object of the key project was to make the measurement in a number of different ways. And the idea was by making these measurements each of the different methods would have its own kind of uncertainties, but by combining them in the end, we could get a stronger constraint on the overall value of the Hubble constant.
And so that's what we did. And we were able to measure the value to 10%, but we've continued to be able to bring down the error bars with time. So here's now starting with our 2001 measurement, the final paper that came out of the key project. And if you look at the values that have been published in the intervening time, until recently, the value has stayed very, very similar.
So it turned out to be in the middle approximately of the 50 to 100 range, something like 72 or 73. But you can see that the uncertainty the size of the error bars for these measurements has come down with time. And then these are measurements now of the temperature of the Big Bang radiation.
So these are tiny fluctuations, different temperatures that you're measuring at different points on the sky and the idea that there would be fluctuations in the temperature in the background radiation was worked out by theorists in the 1970s, but nobody imagined at that time that there would be detectors that were sensitive enough to make these measurements. The differences are about one part in 100,000. It's 1/1000 of a percent. These are differences in temperature that people are measuring now.
And also it's been possible to measure differences in the polarization. And let me just point out, does anybody see anything unusual in this part of the map? If you look really closely, you might be able to see that there's an "S" and an 'H". And we like to joke that the sky has it. But it's just interesting, it's just a random fluctuation, but it really does look like an S and an H.
So with these observations, you can come up with a model to fit these observations that describes the overall composition of the universe, that then describes the evolution of the universe. And if you apply that model, then you can infer how fast the universe would be expanding today. And that's where you come to the 67.
And the model that's used to fit these data is something that is now referred to as the standard cosmological model. And that model now has been with us for over 20 years, going on a quarter of a century. And there are a lot of data that support the standard model, but we don't yet understand the composition of the universe.
It turns out that not only is there matter, matter like we are made out of very on, of the carbon, nitrogen, oxygen all the elements that we're familiar with, but there's a type of matter that is dark in the sense that it doesn't shine, does not emit light. And we infer its existence because of the presence of other matter that, again, by gravitational attraction, impacts the things that do shine, that do have light. So motions of galaxies, motions of stars and so on.
And then it turns out not only is there dark matter, but there is a type of what astronomers now refer to as dark energy that is most of the overall composition of the universe. And this is the quantity that Einstein originally rejected, this cosmological constant. It's causing the universe to speed up in its acceleration. So this is a model that fits the data well, but we don't have a good fundamental understanding of what is the nature, how do we explain the presence of this dark matter.
Now here are the measurements of the microwave background data, the Hubble constant that's inferred when we apply this standard cosmological model to the data from the background radiation. So that value has come down over time. So it originally actually agreed very well with the data from the Hubble project, but with time, the value has come down and the uncertainties come way down. So this is a point here that was measured by a European satellite called Planck.
And this is what gives rise to the 67 that I've been mentioning. And so the issue now is if we compare these on the same scale, there's this wide separation between what you get from the Cepheid's tied into these type 1A supernovae, and the measurements that are coming from the microwave background. And so the question is, how significant is this difference? Because it could be that it's simply some error that we haven't identified, either in the Cepheid's, or in the measurements of microwave background.
The measurements of the microwave background have been tested now, I think, pretty well. There might be small differences that could cause small changes, but not enough to explain this kind of a difference, where the error bars don't even overlap. So nearby, the local measurements of distance, are still challenging, they're still issues that I think we need to show with confidence, are no longer a concern if we are to conclude that there really is something wrong with the standard model. But why this is exciting is that this is how you would tell if there's something wrong with the standard model, is to make really accurate measurements of the current rate at which the universe is expanding, which we do locally.
So just to show you pictorially what we're looking at, so here is the early universe represents the time 380,000 years after the Big Bang. And this is where this Planck satellite is measuring this value of 67 based on differences in temperature that are being measured in the microwave background radiation.
And here we are today, 13.8 billion years old-- the universe now is 13.8 billion years old and making measurements with these Cepheid variables and we get a value of 73. So the question is, is there something that we don't understand that could have happened either before we're seeing the microwave background data or somehow on the way to us that could explain this difference.
OK. So is there new science that we may have missed. Each time, I have to press it more. So one of the projects I became interested in a few years ago was to say, OK, we've made all these measurements with the Cepheid's, it's clear that there's a problem or a discrepancy with the Cepheid's in the microwave background. Can we make this measurement in a different way?
And we started to make measurements of stars known as Red Giant Branch Stars. The sun will eventually become a Red Giant Branch Star. So Cepheid's are young and massive. They have masses maybe 5 to 20 times the mass of our own sun. And these are lower mass. These have masses comparable to the sun.
So in the course of their evolution, they end up in a state where they've used up the hydrogen. For most of their lives stars burn hydrogen into helium and when that's used up, massive stars start to burn the helium, but the low mass stars like the sun, the temperature is not high enough to do that. And so the star collapses until it's very dense, so-called degenerate helium core. And then it's still burning hydrogen in a shell, which is adding material to the helium core. And eventually, the temperature does become high enough to burn helium. And then the star has this thermal nuclear runaway.
At the point that happens, the star then descends onto another feature, another stage of stellar evolution with less luminous. So there's a maximum brightness that these stars can attain. And that's very helpful if you're trying to measure a distance because if you can measure the point at which the stars undergo this so-called helium flash, then you can use that as a distance measure. It's similar to the Cepheid's, but actually simpler than what we do for the Cepheid's.
And so we used Hubble, it started to measure these stars in the outer regions of galaxies, away from the central disks where there's a lot of dust that I've just described, so that we don't have to worry about the dust. And then we use this technique, which is completely independent of the Cepheid's, has different uncertainties, different everything, which makes it independent. And we use that to try and measure the Hubble constant.
So we stepped out again using type 1A supernovae. And we got a value of about 70, approximately, which is right between the 67 and 73. So it suggests that there's something we don't yet understand about the Cepheid's. And that's something that we're trying to very hard to resolve right now. So you can see, actually these Red Giant Branch Stars here, they agree pretty well with the measurements coming from the microwave background shown here.
Also have reasonable agreement with the Cepheid's, but the difference between the tip of the Red Giant Branche, Red Giant Red Stars and the Cepheid's here has nothing to do with the early universe. So we clearly need to understand why this difference, before we can interpret the difference between the Cepheid's and the microwave background as telling us about something is wrong with the standard model of cosmology.
So that's why I'm very excited now about the James Webb Space Telescope. So James Webb is a 6 and 1/2 meter telescope and it's optimized to detect radiation in the infrared. Why do we care about that? These dust particles scatter the radiation primarily at optical wavelengths. And that's what Hubble has been sensitive to.
And so correcting for the presence of dust is harder when you're observing at optical wavelengths than if you observe in the infrared where the dust has a longer wavelength, essentially, it doesn't even see the dust, just goes right through it. And it's also bigger, it's a bigger telescope. It's a 6 and 1/2 meter telescope compared to a 2 and 1/2 meter telescope, the Hubble telescope. So it has higher sensitivity. So you may have seen the launch, heard about the launch, which was a spectacular launch.
This thing is located at what we call the Lagrangian Point, maybe I'll skip that one, come back to it. It's at a distance of about a million miles from the Earth. It's not going to be serviced in the way that the Hubble Space Telescope was. So here is Hubble. It's orbiting about 350 miles above the Earth's surface. So it's orbiting constantly around the Earth.
So when the telescope was launched, it went through the series of deployments, including, as you might have seen, the mirror is in segments, there are 18 different segments to the mirror. And it has this incredible sunshade that has five layers, each of which is about the width of a human hair, and that all had to be unfurled in space. OK. I don't have any backwards motion apparently.
Let me see if I can-- yeah, so as it was traveling out to this L2 orbit, it was unfurling the mirrors, it was unfurling the sun shields. And there were about 350 or so points at which you could have had a single point failure. If any one of those things had gone wrong, this telescope would not have worked and it cannot be serviced. It's a million miles away. And it worked flawlessly.
This is a feat of engineering that I think is just phenomenal. So it took a few months to get out there and open it up and then run through all the calibration and then we started to get data from this telescope. You may have seen images that are really quite beautiful. So here's the Carina Nebula here, this is a nursery where new stars are being born. And I'll show you in a moment, the infrared radiation, as I said, goes through the dust. So you can peer into these clouds. This was one of the earliest images taken of a quintet of galaxies.
There's a deep field within literally a few minutes, it rivaled what the Hubble ultra deep field did, which took months of sitting on the same object region of sky and going as deep as you could. It's going to be spectacular when there's enough time finally to do a deep field with the James Webb.
And even in studying Jupiter, planets in our own solar system, this is going to be a phenomenal telescope for studying planets around other stars and looking at what's in the atmosphere of those stars and perhaps even studying stars with masses comparable to the Earth.
So why does it work so well? So here, you may have seen earlier from Hubble, images, these were called the Pillars of Creation. And this is another stellar nursery, there are stars that are being born in these pillars here. And I think it's really one of the most beautiful images that came out of Hubble. Whoops. She just give up on us. [CHUCKLES]
And here's what happens when you look in near-infrared light from James Webb. And so you can see, all of these stars were blocked by dust in this image here. And now you can just peer right through the dust. So our ability now to study where stars are forming, how they're forming, it's like being able to clear out the fog.
And then you can go into the far infrared, and then you're looking at dust, the radiation that's scattered by the dust. So you're actually looking at the dust properties itself when you go into the mid infrared. So it's a new window on the universe. And Hubble had a little bit of capability to look in the infrared, but not very sensitively and not with high resolution.
So the other thing that James Webb is really built to do is to look back in time and because the universe is expanding, the light that's coming from distant objects, so here's a distant object here as it's traveling and the universe is expanding, the wavelength of light is stretched and it shifted to the red, so-called redshift.
And so if we're looking at really distant objects that are redshifted, then we need to have an infrared sensitive telescope. And as we're looking back in time, as we're looking back in distance, we're also looking back in time because the light from these distant objects left a long time ago, we're now seeing these objects as they were when the stars formed in them. So in astronomy, we actually do have a time machine, an ability to look back and to see directly how galaxies have evolved with time.
So this is going to be a great telescope for doing that. And in addition, so we see the radiation from the Big Bang, we see this cosmic microwave background radiation from about 380,000 years after the Big Bang. And with Hubble, we could look at these fainter smudges, these galaxies at higher redshift but we don't have much information about them.
We know that galaxies formed because we're in one, we see galaxies around us, but there's a region between 380,000 years after the Big Bang where the Big Bang radiation is and where these faint smudges, maybe a billion or 2 billion years after the Big Bang, but astronomers started to refer to that epoch as the dark ages because we have no information about it. And that's what James Webb will see directly.
We can witness the first galaxies to be formed. And you might have heard in the news recently, there have been galaxies that have been discovered with Webb that appear to be very massive, very heavy and all of our current predictions suggest there's no way that galaxies that heavy could have formed so quickly. So that's a mystery that we have yet to solve, but it's something-- we knew we would find something new when we were able to look directly. It's something that we're going to have to understand in the next few years and we don't.
So we can also use Webb to improve our measurements of how fast the universe is expanding, the Hubble constant. And this is something that I'm now working on. Very excited about the new capability with the James Webb because of it's higher sensitivity, bigger mirror, we can collect more light, and the larger mirror is, the resolution with which we can measure individual objects goes up directly in proportion to the size of the primary mirror.
So here's an image of a Cepheid that was found using the Hubble Space Telescope. It was actually found using data in the optical part of the spectrum and then following it up in the infrared. So this is what Hubble's optimized to do. Sorry, what James Webb is optimized to do and Hubble strains to do. So there actually is a little smudge here.
We know that the Cepheid's there in the optical. And this is what happens when we point in the same direction with James Webb. So you can see immediately that this star, unambiguously, is there. And if you compare with the original Hubble image, so you can see these two brighter things here and some bright stuff down here, there you see these things, but how they resolve now into individual stars.
So what we're trying to do is make very accurate measurements of how bright the Cepheid's are and it's going to be much easier with James Webb. And we see this in pretty much all the objects we've looked at so far. Here are the Hubble images and so there's not much signal and they're very blurry. And then we go to James Webb and we really can see these stars for the first time at high resolution, high sensitivity.
So I think this is going to help us address this question, is this difference between 67 and 73 real? Do we have to find a reason having to do with fundamental cosmological differences in the cosmological model or is it something that we're going to learn perhaps about Cepheid's?
So I wanted to say a few words before I end tonight about the Giant Magellan Telescope. And this is the telescope that's scheduled for operations in the early 2030s. And it's a 25 meter telescope. So if we could, sometimes people ask, well, why don't we put a 25 meter in space? It cost $10 billion to put a 6 and 1/2 meter mirror in space and we don't know how to do that yet for a 25 meter.
But these telescopes will be quite complementary because, as I mentioned, the resolution of the telescope goes as the diameter of the primary mirror inversely. So the bigger the mirror, the better the resolution. And this is a telescope that's made of seven individual segments and one in the center here that will be located in the Andes mountains in Chile. And we'll have 10 times the resolution of Hubble.
So the mirror technology is actually quite interesting. These are mirrors that are being made at University of Arizona in their football stadium. And the mirrors are cast in an oven that's rotating. So you put glass into this rotating oven and then you get the original parabolic shape that you need for your mirror. These are actually off axis, the ones in the outer region. So you have to bring the light to a common focus. And there are secondary mirrors at the top of the telescope that actually can move very rapidly on millisecond time scales to correct for the presence of the turbulence in the Earth's atmosphere that we have to worry about on the ground.
So this is a telescope, it will be 20 million times more sensitive than the human eye. So this is a telescope that if we were observing from Syracuse, you could resolve a dime, you could actually see the face on the dime in New York City. So it's a pretty spectacular capability. And if there was an atmosphere on the moon so that we could light a candle, we could see it.
So here is a simulation of a region in a nearby galaxy where you can see here, are these four blobs. So this is pretty good what we call seeing atmospheric, low atmospheric turbulence from a telescope on the ground. And this is what it looks like with the infrared camera on Hubble. So you see it begin to resolve. Here are these four stars again. And this is now what it looks like with JWST, with the near cam that we're using on JWST. So you see immediately how much better the resolution is.
And then here it is with the GMT. So it's an increasing progression in our ability to resolve individual stars that we just are able to keep improving, so again, in terms of measuring these objects that we're measuring with Hubble and JWST, we will be able to improve even further. So let me just leave you with, I think, what's going to be a very exciting next decade. We've already seen in the last couple of decades and last century, an enormous change in our perception of the universe of what we've learned.
The universe is expanding, it's not only expanding, it's accelerating with time. There's matter that we don't yet understand the nature of. And this telescope, James Webb, promises to open up our understanding of the early universe, perhaps let us resolve this question of whether or not there's fundamental physics that we still need to learn that's missing in our standard model. And then new telescopes on the ground that will work in tandem with those in space.
This is a telescope sensitive to optical radiation questions, like is there life on other planets? These new telescopes will have the resolution to actually detect biosignatures, things like water, ozone, carbon dioxide and so on, you need a large telescope to spread the light out into a spectrum to actually measure individual lines. So I think the next few decades are going to be equally exciting as the last few have been. So if there are young students in the audience, I think we've left a lot for you to do. And I encourage you to go into the field. So I'll stop here and happy to answer any questions.
[APPLAUSE]
SPEAKER: OK. Do we have questions for our speaker? I'll bring the mic around so that everyone can hear your question, if you just go ahead and raise your hand. Yes?
AUDIENCE: Thank you very much. One of the important things that Hubble discovered was the expansion of the universe and it's very hard not to imagine something that expands without a center, but the current understanding is there's no center to the universe. Could you comment on that and are there any alternative theories that might posit there being a center somewhere, and would we, in a Copernican sense, be very far from it?
WENDY FREEMAN: Yeah, I think one of the things we've learned in the last several decades, centuries even is that we like to think of ourselves as the center, but each time we learn something new, we realize we're not at the center, beginning with Copernicus and then Shapley and then Hubble.
So it is difficult to visualize because I think when we think of a Big Bang explosion, we think of a bomb and we think of material that flies out from the center of the bomb. And in fact, there is no center, as you're correctly saying. And so what we've come to realize is that early in the universe, there was probably a period of very rapid expansion that has been called inflation.
And the whole universe was expanding. We are not-- there is no center to that explosion. And it's hard to visualize, but one way, I think, that you can get some sense of it, maybe not visualize it, is general relativity is a four dimensional theory. There are three dimensions of space and there's one of time. We don't think in four dimensions. We're used to a three dimensional world.
But if you think of-- I'm just looking for something to hold, but say this advancer here that doesn't work, and you think of the surface, so the two dimensional surface, it's a three dimensional object, but let me ask you just to think of the surface right now. It's two dimensions, right? So if I have an ant on the surface of this thing, it can wander on that surface anywhere it wants. There's no edge to the surface, there's no center to the surface, it's just in two dimensions. This is not something that is expanding into something from a center.
It can walk anywhere on this surface and it's not going to fall off because there is not another-- we're not thinking in three dimensions here, we're thinking in two dimensions. So if we were to make a measurement, say, in the Andromeda galaxy and we looked at other galaxies around us, we're sitting in Andromeda, we would appear to be at the center of that expansion, just as the way we appear to be at the center of the expansion here.
And that's a consequence of there's a uniform expansion. That's what the Big Bang expansion is. So we would measure that anywhere that we were. At the current time, we would see the same expansion and we would appear to be at the center of it, but there is no center to the-- the Big Bang is that explosion of space itself and there is no center.
SPEAKER: Great. Are there other questions? Maybe while folks are thinking of them, I could-- there's one in the back. Oh, there's one here and then we'll go in the back.
AUDIENCE: Thank you. I'm curious, you showed the error bars for the age of the universe as 0.5 billion years, but then said recombination occurs 380,000 years after the Big Bang, there's a whole bunch of other things that happened 10 to the minus 20 seconds after the start. So I'm curious, I didn't realize the imprecision on the 13.8 was so large. And how can we be so precise about the other numbers?
WENDY FREEDMAN: Such a big improvement from anything we've seen.
AUDIENCE: It's not an insult.
WENDY FREEMAN: So I'm just enjoying the fact that you think it's really large because it's-- so there are some things that you can measure in the Big Bang radiation that are really precisely measured. So for example, the temperature of the background radiation is now measured to several significant digits. And this measurement is 67.4 plus or minus 0.5, is a better than 1% precision. So yeah, let me just stop there and say this right now really does represent state of the art.
SPEAKER: Thanks.
AUDIENCE: I'm just curious--
WENDY FREEDMAN: Answer your question, I'm starting to realize-- I have to go back at the site and look. So I may have had the uncertainty in the age that was based on the uncertainty from the measurements locally. Now that I think-- that might have been an old slide. I need to go back and look at that because the age that is coming from the Big Bang might actually be-- the uncertainty of the age may be smaller than that. Yeah. Now that I'm thinking back to that slide, I think they might be a mixture of both the microwave background and the local measurements. Yeah.
AUDIENCE: So I'm just curious about the Giant Magellan Telescope, where you talked about these adaptive optics that operated on a millisecond time scale. How does that work? What are they reacting to?
WENDY FREEDMAN: Yeah, so they're magnetically controlled so it's very thin piece of glass. And the actuators are magnetic and they're very lightweight. So these are 1 meter in diameter, the primary mirrors are 8.4 meters in diameter. And they're constructed so that they can move very rapidly. These have now been developed for the large binocular telescope at the University of Arizona. The technology now has been tested. They work.
And each one of those one meter telescopes will correct for one of the big primary mirrors. So the primary mirrors have actuators on the back that are mechanical. And they operate every 30 seconds. So they're changing the shape of the primary. The secondary mirrors are moving on millisecond time scales and they're actually-- so they're using laser.
So there are a cluster of sodium lasers that shoot up into the atmosphere, there's a layer of sodium up there that act as an artificial guide star. And so you do that and then you get the response and you get the information you need to deform the mirror of millisecond timescales.
SPEAKER: Great. Yeah-- oh I see.
AUDIENCE: So we have out there, a focal pendulum. And I'm not remembering this very well, but Einstein was inspired by something that Mark said, and this demonstration, at some level, tells us that we're in an inertial reference frame if we take away motions that we know about. They're spinning and stuff like that. So that's a local experiment. And it tells us, in some sense, something cosmological.
Is there any modern day version of this that has to do with, say, the operation of an atomic clock or an interferometer that you would orient around. Because in a sense, we're at the-- according to that, we're at the center of the universe, with respect to the velocity, respect to the rest frame of the Big Bang. So is there any time in which the incredible precision of atomic experiments that we're hearing about, it tells us again, something cosmological in the way that focal told us back in those days?
WENDY FREEDMAN: So not right off the top of my head in the sense that you're asking. There may be other physicists in the audience who might be able to answer that. Not in the context that you're asking, nothing comes to mind at the moment.
AUDIENCE: Sometimes people are worried about the distortion leading to this.
WENDY FREEDMAN: Yeah, no evidence-- no evidence for that. So, again, measurements of microwave background, you don't see any evidence for rotation. People have measured galaxy distributions and motions of galaxies and you don't see evidence for that and it would show up in the microwave background.
SPEAKER: All right. Are there any last questions? Yes?
AUDIENCE: Thank you. Can you sort of illustrate the space of problems that GMT will be able to do that JWST can't? And does it just take over the whole thing or is there still stuff that you can do out in space better because without the atmosphere?
WENDY FREEDMAN: Yeah, they're complementary again. So there are features, for example, one I was talking about, the spectrum of exoplanets, most of the features that the water and ozone and so on are actually seen in the optical, but there are some transitions that are in the infrared.
So GMT will have the spectral resolution. You need about 1 kilometer per second resolution to measure the velocity of an Earth mass planets and actually get the density in the mass. So you need those to know that you have an Earth mass planet. And you won't do that with the James Webb, but you will have the infrared part of the spectrum.
And so it's the combination of those lines. You see what you get in the optical, you predict what you would have in the infrared that would give you some confidence in that particular case. So particularly for spectroscopy, because you need a big light bucket if you're going to spread the light out and measure a spectral features, GMT will be, I think, the spectral instrument and JWST, again, has the infrared capability, which we don't have the ground.
So they are really quite complementary. You don't want one without the other and we've seen that with Hubble and Keck, for example. So you had the really deep images that came from the Hubble Space Telescope and the deep field. But if you hadn't had Keck or Magellan to take spectra of those objects, you wouldn't know how far away they were, you wouldn't;t know what kinds of galaxies they were. So they really do very complementary kinds of science. And if you read the science cases for each of them, they sound very similar, but they're coming at it from a different point of view.
SPEAKER: Oh, there's one other question here.
AUDIENCE: Correct me if I'm wrong, but I'm pretty sure I've heard James Webb probably only has enough fuel for around 10 years. And given it took 20 years to develop, are there any other space-based telescopes on the pipeline?
WENDY FREEDMAN: So the answer quickly, yes, there are other ones in the pipeline, but the really nice thing about Webb is that because the launch was so flawless, they actually didn't use up all the fuel that they had just in case they needed to make corrections to the course of the telescope. So they're now projecting a lifetime of between 20 and 30 years.
So there is some station keeping-- so the Lagrange point where the telescope is approximately stable, but it does require a small little orbit. So occasionally, they need to give it a little bit of a kick. But they're now projecting that it will last maybe for 30 years, which is phenomenal. But yes, there already are plans on the drawing board for-- there's a telescope, large optical UV telescope that would be the successor to Hubble. And it will be very good for the study of exoplanets.
There's a telescope called Lisa that will measure gravitational waves from black holes and that scheduled for the mid 2030s. And of course, there are ground-based facilities also. There's new-- the CMDS4, it's another cosmic microwave background large project.
There is something called the Simons observatory that's happening, people here are very much involved in that. And then there are three extremely large telescopes on the ground. There's a Giant Magellan, there's another one that's a partnership of China, Japan, India, and Caltech and you see-- and there's a European telescope. So there's a lot coming in the next couple of decades. Yeah.
SPEAKER: I think I saw a hand down here and then maybe we'll have time for one more and then we should wrap up.
WENDY FREEDMAN: We're keeping you busy.
SPEAKER: It's good.
AUDIENCE: Thank you. Thanks very much for a beautiful talk, very inspiring. So you taught us a lot about the science tonight, but I know that you personally have been involved in some of the most astonishing discoveries of the past, I don't know what, several decades.
You didn't tell us too much about how it felt to have discovered some of the things that you were-- I realize you're part of a team that made discoveries, but if you're open to it, could you share what was one of the most surprising discoveries that you were part of and help us feel like we were a fly on the wall when it was happening?
WENDY FREEDMAN: Well, I will say, I feel really fortunate to have been a scientist at the time that I was able to become a scientist for many reasons. So we were looking at the photograph early on of the physics department here at the time of the Hans Bethe. And we sort of noticed there were no women there.
So that changed and I feel really fortunate to be living at a time when I could have a career in science. So one of the things that happened early in the project when we were planning for the proposal stage, the director of the Space Telescope Science Institute at the time was a man named Riccardo Giacconi. And he was concerned because Hubble was the first telescope, optical telescope, that you could observe above the atmosphere.
And he knew that it was going to be highly oversubscribed and astronomers were really going to want to get a lot of time on it and so he thought, if there was a Time Allocation Committee, which is what we do to decide who gets time on a telescope, we write a proposal the time Allocation Committee makes the proposals. They left it up to them, they would slice the time into tiny little pieces so that everybody could have a little bit.
And he was worried that there were some things that only the Hubble Space Telescope could do and they would require more time. He invited the community to propose for what he called, key projects. And so the Hubble Key project was one of the ones that ended up being a key project. And so we had a theorist in our group.
And we were proposing to measure Cepheid's in what's called the Virgo Cluster, this is the nearest cluster to us. And the theorists went away and made some estimates based on Cepheid's in our Milky Way galaxy, saying you'll never discover Cepheids in Virgo, it's not possible.
So the telescope was launched and then the sphere of collaboration was discovered, that the telescope couldn't focus. So that was a real setback. And the first object that we observed when the telescope had been repaired was a galaxy in the Virgo Cluster. So I was sitting in my office one Saturday afternoon, reducing the data and went to look for Cepheid's, look for stars that were varying that might be characteristic of these Cepheid variables and they start to pop out.
And there were just tons of them. The amplitudes were large and the errors were really small. And it was so obvious we could do the project. And that was a moment of real enjoyment. No one had seen this before, no one had-- and at that moment, I knew, OK, we can resolve this factor of two discrepancy, this is going to happen. It took 10 years. At two dozen galaxies and really make sure that everything-- all the T's were crossed and the I's were dotted and check for errors, et cetera, et cetera. But that was a moment that I remember fondly.
SPEAKER: Great. Thanks for all of your questions and thanks, everyone for coming. Thank you for giving this talk and all the talks this week. It's been amazing. Just a little note, so if you go to the physical science building atrium, there's a reception if you want to have some snacks after the talk, but let's give our speaker another round of applause and thank you all.
[APPLAUSE]
7:30 pm, Schwartz Auditorium, Rockefeller Hall
