Space oddities - with Harry Cliff

On New Year's Eve, 1859, Edmund Larbo, a country doctor from a small town on the outskirts of Paris, is sitting at home, possibly waiting for a nice New Year's Eve dinner with his family, when someone unexpectedly knocks on the door as he opens it, and surprised to find. himself facing the imposing figure of Urbane Lear, France's most famous astronomer and director of the imperial observatory in Paris, now without even asking how you do it, Urban L pushes his way into Lear's hallway demanding to inspect his astronomical equipment. . You also see Leabo. as tending to the aches and pains of the local community he is an enthusiastic amateur astronomer and about a week earlier he wrote a letter to Larier telling him about a strange object he saw crossing the face of the Sun earlier that year.

Now this letter is like this. He tells L that despite it being New Year's Eve, he immediately jumped on a train and just a few hours later he was banging on poor old Leco Abo's front door, so why was there so much rampage? Well, he had been worried about the orbit of the planet Mercury for a long time. Now, um, this image on the slide shows, hopefully, this works. Sorry, it's not on. What you see here is a transit of the planet Mercury across the face of the Sun, as photographed by a NASA

space

craft. Mercury had repeatedly embarrassed astronomers throughout the 19th century when they discovered that they missed its transit sometimes by hours, in one extreme case, by an entire day.

Now in a universe that was supposed to run like a clock according to Newton's law of gravity, a planet with such poor timekeeping was actually very worrying, in fact now Larier had recently done it. solved a similar problem with the orbit of the planet Uranus by proposing the existence of an invisible eighth planet whose gravitational pull was subtly altering the orbit of Uranus and when astronomers pointed their telescopes at the point in the sky he later told them they discovered an eighth planet, Neptune. So I thought I could perform the same trick twice, essentially, maybe Mercury's strange orbit is explained by another ninth planet, this time between Mercury's orbit and the Sun, so when he read Les Bo's letter he immediately thought that maybe this rural doctor.

He has actually discovered my hypothetical world, so he now finds himself in Les Garbo's hallway, so he subjects the Observatory to him to some sort of exhaustive investigation. He finds it relatively satisfying. Then he subjects Leabo to an intense interrogation that one, uh, tells. compared to the meeting of a lion and a lamb, uh, and then, to solve it, he goes around the town and demands character witnesses from the residents of Les Garbo to prove that he is not being deceived by a scammer, but at the end of the day he returns to Paris is convinced that his new planet has indeed been found and on January 2, just a couple of days later, he announces to the world the discovery of a planet that he calls Vulcan in honor of the Roman god of fire, which causes an international sensation.

Headlines throughout France and Britain about the discovery of a ninth planet in the solar system and Larbo finds himself catapulted from obscure country doctor to being condemned by the great and good of the astronomical community and receives the Lion Don for his discovery. Now Larier based on Alco's observations calculates the next time Vulcan should transit the Sun but when astronomers look for it they do not see it and this continues throughout the 19th century for decades an exhaustive search for Vulcan is carried out occasionally there are sporadic sightings, but no one manages to predictably identify where this planet really is and, at the beginning of the 20th century, astronomers are forced to accept that the supposed World Vulcan of L does not actually exist, so what was happening there is still, However, one problem is an anomaly with Mercury's orbit, so this is essentially what is happening.

What you can see here in this little animation is a planet orbiting the Sun. Now Mercury, like all planets, orbits the Sun in an ellipse, but this ellipse does not remain fixed in

space

. actually renders, you can see this ellipse is rotating. This is due to the gravitational pull of other planets in the solar system, but when you predict the speed of this procession using Newton's law of gravity, you get the wrong answer. Mercury actually processes slightly. faster than predicted now, this is a small effect, it basically means that Mercury makes an extra orbit every 12 million Mercury years, so we are talking about a 1 in 12 million anomaly, but nevertheless, it turns out that it cannot be explained by Newton's law of gravity.

This anomaly had a much deeper implication than the discovery of simply another planet. In reality, it was a clue to a radically new picture of space-time and gravity itself. The solution was finally found by this man, so hopefully you recognize him as Albert Einstein, but not how you are used to seeing him, this is him at the height of his powers in his 30s and in 2015 he was putting the finishing touches on what would be his masterpiece, a theory, a radical new theory of space, time and gravity that is known. as general relativity now as the first test of his new theory Einstein tried to calculate the procession of Mercury's orbit and found an answer that exactly matched the astronomical predictions now Einstein was apparently so overwhelmed by this that he actually had heart palpitations and had to lie This was the culmination of essentially seven years of hard SLO and one of the things Einstein said about this moment, he said it made me appreciate the fastidiousness and pedanticity of the astronomers I used to make fun of in the past, essentially what This small anomaly was a clue to one of the most profound realizations of modern physics: general relativity transformed our understanding of the universe, led to the Big Bang theory, led to black holes, gravitational waves and many more, and that's it one's. small anomaly now essentially the reason this anomaly appears is because Einstein eliminated in a sense the force of gravity, he said that in reality there is no such thing as gravity, what really happens is that a massive body like the sun deforms the structure of SpaceTime, so imagine that the classical analogy is to imagine SpaceTime as a kind of elastic sheet and a heavy body like the sun bends SpaceTime around it and this curvature is most extreme near the Sun and as Mercury is the innermost planet , that's where The difference between Einstein's theory and Newton's theory is most evident, so I tell you this story really to illustrate the power of anomalies.

Anomalies are essentially small deviations, often from our expectations based on our current theories, and sometimes they can be the key to gaining deep insights into the world around us and that is what this talk today will be about and also what My book Space Oddities is about, it is about both past and present anomalies that challenge our understanding of the Universe. I'm going to start with a quote that is very close to my heart, so this is a quote from the American science fiction writer Isaac Azimov, who says that the most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka.

I found it, but H. That's funny, so I'm going to tell you about a lot of funny things that are happening in physics right now, but to start, let me set the stage, so why do we think there are new things in fundamental physics to be discovered? There is a lot about the world and we have discovered a lot in the last century since the story I just told you and our knowledge of the universe is summarized in two extremely successful theories that we refer to rather boringly as the standard models. the standard model of particle physics, this diagram essentially represents the known elementary particles that make up the world around us, the forces that allow them to interact with each other, it is described by a very beautiful and elegant piece of mathematical theory, the standard model is One of the most successful theories in history explains everything from the structure of atoms to how the Sun shines.

At the other end of the scale, this is the theory of the very small. We also have a standard model of the very, very large, now we know from Astron. When you look out into the universe, for example when you look at galaxies, there is a lot of invisible material in the universe. In the 1970s, astronomers discovered that stars orbit galaxies too quickly for the amount of matter we see to keep them gravitationally bound. and this led to the understanding that there is a large amount of matter called Dark Matter, essentially a kind of invisible substance that provides additional gravity that holds galaxies together and, looking even further, at the galaxies themselves, we see that the universe is expanding and in the 1990s it was discovered that this expansion is actually accelerating and this led to the discovery of another dark thing known as dark energy, which is a type of repulsive force that is causing the universe to become increasingly bigger at an increasing rate, so this pie chart essentially represents what cosmology tells us that the universe is made of that 5% sliver that you can see, which is labeled atoms, that's us, that's the Earth, that's all we can see in the night sky, every star, every galaxy, every dust cloud or speck of dust now.

That's what the Standard Model of particle physics describes, so this tremendously successful Microworld theory, which in some sense was the closest we've ever come to a Theory of Everything, only describes 5% of what's there. outside, the rest. 27% Dark Matter 68% Dark Energy We have no idea what they are and this is one of the main reasons why we believe there is more to discover in the universe. Now, this description of the universe is encapsulated in a theory known as the standard. cosmological model that essentially describes the history of the universe beginning with a very rapid period of expansion known as inflation that gave rise to the big bang and then the universe has been expanding ever since with dark energy gradually accelerating that expansion later in its history, by What We have these two tremendously successful models, but in a sense they are in conflict with each other.

The standard model of particle physics can't explain much about what we actually see up there in the universe, so I'll tell you two. Tonight I will tell stories about two anomalies, one that comes from a very small scale, the world of particles, and another that comes from the largest scales, the scale of the universe as a whole, so I'm going to start with a demonstration, so I hope we were all handed half of what looked like 3D glasses when they came in, so what am I going to do? If we could dim the lights a little bit please what I have here is a hydraulic lamp so essentially there's a little container of hydrogen here and it's going to pass a high voltage electrical current through now the first thing I want you to do is just I can spin this for a moment, so if you hold the thing up to your eye and look in the lamp, I'll give it a little spin so you can see it and hopefully also for those watching on the live stream, you'll be able to see this because the cameraman will be kind enough to hold the diffraction grating to the camera what I hope you can see are two lines that you don't see or maybe it's not pointed at you, yes it's just gradually appearing.

Can you see anything? People see something. Yeah, so what colors can you see? Fuchsia and fuchsia. red, yeah, so I'll do it. I'll keep doing this a little bit more so you can take a look, so what you're looking at is a defraction grating, so what it does is it splits the light from the hydrogen lamp into a rainbow spectrum and what you see is that there are really only two prominent colors there. I'll disable it. Thank you very much if you didn't see it, that's what you should have seen. So, what you are seeing there you are seeing. an effect of quantum mechanics, you are seeing evidence with your own eyes of quantum mechanics, so what is really going on?

Well you're looking here at this, like I said, in this container is hydrogen, hydrogen is the simplest atom, it's a single proton orbited by a single electron now, according to quantum mechanics, electrons cannot orbit a proton at any distance as planets can orbit the sun, they can only orbit at strictly quantized energy levels at certain distances essentially from the nucleus, now normally hydrogen, the electron would be at the lowest level. Energy state, you can see these various orbitals, the lowest one labeled n equals 1 is where the electron would normally be, but by passing this very high electrical voltage through the hydrogen, you excite the electron to a higher orbital. and then what happens is it falls back to the lower orbital, so look, we have an electron hanging around in the third oral orbit and if I press a buttonmagic, Quantum will jump to the second orbital and emit a photon, so the photon that is emitted takes the energy difference between those two levels and that produces that red band that you can see.

Another thing that can happen is that the electron can be in the fourth energy level and similarly can make a quantum jump and fall into the second energy. level and this time it emits some kind of bluish photon of slightly higher energy, so that's what you're seeing. Those two lines you saw are essentially quantum jumps in a hydrogen atom. Now there was a crucial anomaly that was discovered related to these same ones. transitions back in 1947 and this discovery was made by a man called Willis Lamb and his assistant Retherford and essentially what they had done is they had spent their time heating hydrogen atoms in the microwave and in the process they had discovered that in this second orbital in which we can see the electron moving, in which these transitions were taking place, in reality it was not a single energy level, but two energy levels with very subtly different energies, in fact, the difference in energy was small, it was approximately one. part in a million may not seem like a big deal now, but when Lamb went to this, this is a photo of a conference that took place in 1947 on Shelter Island, near New York, and it was the first major conference where the kind of The Galacticos of the world of theoretical and experimental physics came together again after World War II.

Oppenheimer was there, for example, so what you can see here, Lamb is the guy leaning over the table and there's an interesting discussion in the middle is Richard Feeman and on the right is Julian Schwinger and the Lamb anomaly, one between one million, was actually a crucial clue that allowed Fineman Schwinger and several others to form what is now the basis of our understanding of the physical world. This was really the beginning of what we call quantum field theory, so quantum field theory says something quite strange which is actually that particles like electrons and quantum marks are not really fundamental in some sense, they are manifestations of much less tangible and more ethereal substances known as quantum fields, so you can think of a quantum field as a kind of invisible fluid that permeates the entire universe and in this image a particle like an electron is just a wave, essentially a vibration in this invisible field that fills the entire universe, which means that every electron and every atom in our bodies is just a small vibration in this universal field of electrons that surrounds us.

We now know about 17 particles in this standard model of particle physics, which means there are 17 fields. This has a fairly profound implication for what do we mean when we talk about space? What do we really mean by empty space in this image? Well, what would you consider empty space? Imagine going to some distant part of the universe. Intergalactic space where there are very few things and you build a box and you suck up every stray atom you literally run out of nothing what nothing looks like in this image well it actually looks pretty interesting this is an image of nothing an animation of nothing um so what you're seeing here this is from the University of Adelaide is a vibrational simulation of subtle quantum vibrations in these quantum fields that are always there in a vacuum, so essentially, even when there are no particles there because of quantum uncertainty, these fields They glow constantly and tremble like a With a gentle breeze on the surface of a pond you can see this incredible churning quantum motion and, in reality, what Lamb had seen, this subtle change between these two energy levels in hydrogen, was in fact actually the influence of empty space on the orbit of an electron as it moved around the planet.

Basically, one orbit of the atom was hit harder than the other by these quantum fluctuations and led to a very small difference in energy and it was this crucial clue, small one in a million anomaly, that led to this profound new understanding of the microworld. and quantum field theory. is now the language with which we describe all of modern particle physics, so this is a great moment in the history of physics, but I'm going to move on to the real anomaly that worries physicists today: the fact that That the void has all of these The fields it contains gives us an amazing tool to probe things we haven't seen yet, so I'll show you how we can do this.

This is a particle called muan, well actually it's not, it's an image. I drew one, but you may not have heard of a muan, it's essentially a heavy electron, so the muon is a companion to the electron; In fact, it is exactly the same as an electron, except that it is 200 times heavier and does not live very long. Muons only live for about a millionth of a second and then they decay, but there are actually muons in this room right now. They are produced by cosmic rays that hit the upper atmosphere and fly through the Earth's atmosphere and down to the ground. few of them pass through you at any time, now a muon like an electron is electrically charged and also has a property called spin, so it's essentially as if the muon is spinning on its axis.

Now, thanks to Michael Faraday, we know that if you have a spinning electric charge, you also get a magnetic field, so Farad did experiments where you know electric currents pass around the loops. A magnetic field is produced. A spinning muon behaves a bit like a moving electric current and you get a magnetic field. Why is it magnetic? interesting field of a muon, well this is why the muon doesn't actually sit alone in a vacuum, but it's actually surrounded by all these quantum fluctuations, so these kinds of vibrations that are happening in these 17 fields that I mentioned earlier and This means that when you measure the magnetism of a muon, you are actually not just measuring the magnetism of a muon, you are measuring the magnetism of a muon plus all of its interaction with quantum fluctuations in the vacuum and that It means that if there are new quantum fields that we haven't seen before, for example, if there is a quantum field, dark matter is a vibration, that dark matter field is also in a vacuum and can contribute to the magnetism of muons, so If you make a very, very precise measurement of what magnetic muons are like and then make a very precise theoretical prediction of all these quantum fluctuations based on what we already know and you see a difference that a subtle difference can tell you about the existence of, say, potentially dark. matter or some other new force that we've never seen before, so it's a tremendously interesting thing to do, and in fact, physicists have spent decades making more and more precise measurements of this little bar magnet that the muon has been carrying around with it for longer.

About 20 years ago, an experiment was carried out, one of the last in the series of experiments that measured this property at Brook Haven, near New York, they used this big magnetic ring that you can see behind me, they essentially shot muons around of the ring and as a result the muons went around the ring they measured how magnetic they were and this is what they found so the experiment measured magnetism with tremendous precision so this is a number obviously don't worry too much for what it means, well, what you should notice. There are many decimal places and this is the experimental measurement and this was at that time the theoretical prediction.

Now if you compare these two numbers you see that they agree pretty well until you get to the last four digits, um, so we have this disagreement essentially in the last four digits now if we compare that these measurements and the prediction actually come with what we call uncertainty , which is an expression of how well we think we have measured the quantity or how well we have calculated it. So you can see the uncertainty that's right at the end, the uncertainty is about 63, but the difference between these two is actually much larger than that, so I'm very pleased with this animation, so if you take these two things and You subtract from each other you get the difference between experiment and theory which took a long time to actually make PowerPoint, right? um and what they found when they did this calculation that the difference between theory and experiment actually existed was more than three times the combined uncertainty in the measurement and in the prediction, so this was potentially a clue to the existence of some new quantum field that we have never seen before, which in principle is tremendously exciting, so this is around 2006, unfortunately, when Faced with an anomaly like this, you cannot immediately conclude that you should book a flight to Stockholm to receive the Nobel Prize because there are often boring explanations for what you're seeing that aren't the discovery of some new force of nature.

The number one boring explanation is that you made a mistake in your experiment and this is happening now. Physicists are very careful and do their best to do the best experiments they can, but you can never eliminate the possibility that you may have missed something, so that's one. option, the second option is that the result is a fluke, in other words, because you have some uncertainty in your measurement that that value that you got could have landed anywhere, basically, in a band and it is possible that just by pure luck has finished. or bad luck maybe ended up with a result that was quite far from the theoretical prediction, so it could just be a fluke, the further away the last option is, the theorists forgot to carry one, so what I mean by this are actually these calculations to calculate the mu1 magnet are a correct guess by Fishlyn or in fact in one case with this same prediction you get an exchange of a plus for a minus that actually happened and led people to think that They were discovering something when they weren't, so all of These three things can happen, so you have to eliminate these three options before you can conclude that you are actually discovering something new.

Fortunately, by 2006 the old experiment at Brook Haven had closed and I really wasn't going to be able to collect any more. data, so members of that original team got together and began planning an improved version of what became known as the muong G minus 2 experiment. This was to be a completely new experiment built from scratch at the Fery laboratory near Chicago, the only part of the old experiment they were going to reuse was a superconducting ring that provided the magnetic field that the muons rotate inside, so essentially what they had to do was ship this giant ring from Brook Haven down the Atlantic coast of North America around Florida through hurricane alley. and then up the mississippi river on a barge to essentially reach the suburbs of chicago before they put it on a big truck and closed the freeways and brought it to fermilab and here's a nice little video from brookhaven, this is the ring being removed. from Brook Haven you can see it's an operation, then it's loaded onto this flatbed truck and wrapped in white plastic to protect it.

Now there's a funny story about this, which is that there was a rumor, sort of an urban legend, on Long Island that in the 1960s a UFO had crashed and the white coats had immediately taken it behind the walls of the Brook Haven's laboratory and then, lo and behold, decades later, a thing that everyone thinks is a flying sorcerer. emerges from the lab doors now it didn't help that the moving company has actually taped a small green alien in what appears to be the cockpit. Chris Polly, who was the spokesperson for the experiment, when I interviewed him for the book told me that they told the local residents that they set up deck chairs to watch this strange procession in the middle of the night and a guy came up to him and said: " "You can't tell me it's not a fucking spaceship." Anyway, it wasn't. a spaceship was a magnet um and it came to my lab it was set up they completely rebuilt the experiment you all know this is this experiment is extraordinarily sophisticated it's um Chris described it as if it was like a 600 ton Swiss watch you have to act to measure the strength of your magnetic field with incredible precision, the detectors were already built, controlling the temperature and humidity in the building to the final degree, so it was a really impressive experiment, that's how it works, so now, Dan, I need that you come and bring me. a rope, this is not because the conversation is going very badly.

I hope, thanks, this is where everything goes wrong, so what I'm going to try to show you is basically how the MU gon experiment works, so remember. We said the muan is spinning and then to represent the muon, I have this bicycle wheel, so what happens is essentially you have muons that are spinning.They shoot into this magnetic ring and they're all polarized, so they're spinning. The axle is in their direction of travel, so they are turning in one direction, so if I spin this bike, I hope it works and I let it go. This is what we call a procession, so you can see the wheel processing and turning now. the string moves a little bit which masks the effect slightly but essentially as the muons spin around the ring they do the same thing this bicycle wheel does and they are spin axis processes in the magnetic field so You can see in the little diagram, this is going to hit me in the face, they are changing angles and the speed at which they process tells you how strong the little magnet bar of the mu is, so by measuring the procession speed, you measure the magnetism of the muon that is.

Basically how it works well thanks Dan you can get the rope back for now at least um thanks um you're easily impressed um got it thanks so they took their data, analyzed the first year of data and in April 2021 we were ready to announce to the world the new measurement of muon magnetism and to everyone's delight, the new measurement landed on top of the old Brook Haven result that caused this to happen, so you have new headlines in the press. world of The New York Times tiny particles Oscillation alters the known laws of physics, it's a bit of a stretch, but that's okay, the Bly did it a little better.

Muons. Strong evidence for a new force of nature was found, essentially by measuring this property again with a different experiment. A completely different team had virtually eliminated two of the boring explanations. It seemed very unlikely now that this was just an error in the experiment because you have two independent experiments and they get the same answer also because now you have two measurements. With similar uncertainties when you combine them, their combined uncertainty becomes smaller and that makes the probability that it is a random chance is much less; In fact, there was now only a one in 40,000 chance that this anomaly could be explained simply by sheer luck, so there's no explanation that we haven't eliminated yet and this is where it gets a little murky, so here's a little diagram. which illustrates the situation when the result was announced so that you have your theoretical prediction which is a little lower than your experimental measurement.

I can see, based on the uncertainties, that these two points are quite far apart. Now there's always a twist when you think things are going well, which was the same day the Muong G minus 2 experiment published its new measurement on a rival team. of theorists published a new theoretical prediction of muon magnetism and their result came much closer to the experiment, so if you believe that one theory is a gold PL anomaly, it seems that you are really looking at something fundamentally new that could be a track. to something very exciting if you believe the other group of theorists, there is nothing to see here, basically now you are wondering how two different groups of theorists can get two different answers and it's not just because one of them forgot to bring a , OK?

It is much more complicated, basically calculating the magnetism of a mu1 is something very, very difficult to do. You have to take into account all these quantum fluctuations of 17 different quantum fields that we know in the standard model and in particular there are a lot of fields that are very difficult to calculate these are the fields that essentially produce the nuclear material in an atom, so these are particles known as quarks and gluons now for technical reasons that I won't go into and also once I didn't understand that Well, quarks and gluons, in the theory of quarks and gluons it is very difficult to do manageable calculations, for approximations have to be made to obtain the contribution of the quark and gluon fields, and these two theoretical groups use different approaches. one uses a sort of data-driven approach and the other uses a prime-first approach using essentially a large supercomputer, so the situation we're in now is that we don't know if this anomaly really is the key to something big and could be massive.

You know, a possible explanation for this anomaly is that the muon is being affected by what we call dark forces, so this is not something from Harry Potter, it is actually like this, we know that the universe is dominated by dark matter and, in principle, it is possible that just like ordinary matter, the Universe has its set of forces, electromagnetism and nuclear forces, dark matter may also have its own set of forces through which it interacts and could do so, and one explanation for this anomaly among many is that the Dark Forces are affecting the magnetism of matter. muon or it could be that we don't understand the physics of quarks and gluons properly, so to solve this story theorists will really have to scramble and come up with a consensus prediction about the magnetism of muons, so this is a classic story of How anomalies work can sometimes lead to a breakthrough in your understanding, but even when they don't, they often improve your understanding of current science, so even if at the end of all this massive effort everyone has made to measure This little magnet we discover that there is no new physics;

We will have learned a lot not only in terms of experimental techniques but also in terms of the physics of the fundamental ingredients of our universe that we do know, so it is never a wasted effort, although, of course, we all hope it will be something exciting, So now I'm going to shift to the other end of the scale and tell you a second story, this time an anomaly that has been occupying the field of cosmology for the better part of a decade. Now, to tell this story, I'm going to take you back in time, right after Einstein came up with his theory of general relativity, so back in the 1920s there was a big debate in astronomy about the size of the universe.

There were these objects that were seen in the night sky at one time known as spiral nebulae, these kinds of swirling blobs, and there was disagreement about whether these swirly things were just clouds of dust and gas within the Milky Way. or maybe galaxies. in its own right outside the Milky Way, so at that time the view was that the Universe was a galaxy, so an island of stars in the middle of this endless blackness to solve this I had to find a way to measure distances to these nebulous spirals. and this is something that the American astronomer Edwin Hubble spent a lot of time using the Hooker telescope on Mount Wilson in an attempt to unravel.

Now the problem of measuring distances in astronomy can be summed up in this beautiful scene from Father Ted where Ted tries to explain to his foolish fellow priest Dugall the differences between a small cow that is close and a large cow that is far away um now I'm not saying that the astronomers be as dumb as dle but they have the same problem essentially and I have a good video that the ri demo team Dan put together which is essentially two lamps or they were in the hallway hopefully oh actually no , I was wrong, oh, how is everything there?

Sorry I skipped a slide, apologies, I hope this works. Will you reproduce? No, he doesn't want to play, let's try this. Okay, so these are two lamps. Now they have different brightnesses and different distances, but I think you would have a hard time knowing which ones are farther away until the lights come on. You reveal that one of them is actually the end of Corridor r, the other is much closer, so they have the same problem that you don't know if a star is big and bright but far away or small and dim but close and the La person who allowed us to essentially discover how far away things are in the universe, at least things beyond our local galactic neighborhood, is this woman.

This is Henrietta Swan Levich, she was a pioneering astronomer of the late 19th and early 20th centuries and she spent much of her life there. time stud studies a type of star known as a seid, so seids are young, bright stars that have this pulsating atmosphere, so they grow and shrink over time and hopefully you can see in this animation that this star is pulsing and therefore become brighter and dimmer as they go. you look at them through a telescope now Levit discovered that there was a relationship between how fast this star was pulsating, essentially the heart rate of this star, and how bright it was, so stars that pulsated more slowly were brighter. , stars that pulsed faster were dimmer and yes you could calibrate this.

This would allow you to measure distances because you could look at a seid in a distant galaxy. You could measure his pulse period very easily because you just count, essentially, time him over a period of days or weeks and then you know by his pulse. period, how bright it is and if you know how bright it is, you know how far it is from how bright it appears in your telescope, so suddenly now you have a ladder, essentially a distance ladder that allows you to measure distances when the Hubble did this. He found seidas in Andromeda, which is the largest spiral nebula in the night sky, and discovered that Andromeda was a million light years away, much larger than the stated size of the galaxy at that time, which showed that there were galaxies outside the Milky Way (now Hubble).

She spent the next few years massively expanding the size of the universe by making similar measurements on a large number of galaxies outside the Milky Way and discovered this extraordinary relationship, which was that there was a relationship between how far away a galaxy is and how fast it is moving. . far from us, so Vestos slea observed that almost all the galaxies in the night sky are moving away from us and he discovered this by essentially looking at the light from those galaxies because they are moving away, their light is what we call redshift. extends to longer wavelengths, this is the same effect you get when an ambulance passes you on the street and its siren goes from a high pitch to a low pitch.

The same thing happens with light, so you measure the speed from this kind of stretching of light and you measure the distance using Henrietta Swan's levit seids and when you do this and plot it on a graph, you find that the further away a light is. galaxy, the faster it moves away from us essentially, what Hubble had discovered was that the universe is expanding now. I'm going to try to demonstrate this, this could go horribly wrong, so it's quite difficult to imagine a three dimensional space, so what's really happening here is that the space between galaxies is getting bigger now, this is quite difficult to imagine, but if Reducing the universe to a two-dimensional object is a little easier, so what I have here, which the r demo team kindly provided to me, is a black balloon with some nice galaxies attached to it and now I'm going to turn on an air pump. and hopefully not everything will explode, it will be quite loud, although here we go, so as the balloon grows I will get further away, all the galaxies are getting further and further apart and the further they get from each other the faster they retreat.

So I'm going to stop this before it really has a big explosion, so we'll let the universe slowly deflate now. I don't know how educational that really was, but did it help now? So Hubble described this relationship that he became. known as Hubbles' law. I don't think he called it Hubbles' law. I guess other people did it and it's a very simple equation, so basically V, which is the speed at which the galaxy is moving away from us, is related to its distance d by this parameter H kn. which is what became known as the Hubble Constant, now Hubble and his colleague Humon made the first measurement of the Hubble Constant in 1931 and got this number, so it's probably pretty inscrutable.

They got 500 kilometers per second through Mega Parc, so what does that mean? It means that a galaxy a megapark away will move away from us at 500 kilometers per second. What is a megapark? It's about 3 million light years away, so basically it's very far away, so we're talking about very large distances. Intergalactic distances The problem with this measurement of the Hubble constant was that essentially this means that the universe is expanding very quickly, the larger the Hubble constant, the faster space is expanding. This meant that if you rewound the clock to the Big Bang, the universe just ended.

It's about a billion years old, but if you talk to a geologist, there's a little bit of a problem with this because they've found rocks that are three or four billion years old, so it seemed like the Earth was somehow older than the universe. same and As astronomers made more and more precise measurements, they gradually realized that there were actually some errors in the original Hubble analysis, the number dropped to 180 and then fell again to 100 km per second in the 1970s, in fact, in the 1970s there was thisfierce debate between two different ones. groups of astronomers one who thought the Hubble constant was 100 another who thought it was 50 so this is essentially because measuring distances is difficult, the difficulty here is that actually the key thing to do is measure how far is a galaxy and what is very, very difficult to do even using Henrieta Swan Lev's seid variables.

Now, this Hubble constant is where the anomaly finally comes to fruition. Now is where the anomaly that cosmologists occupy today lives, but it's not this 100 versus 50, it's much more subtle than this. but just to establish why this matters, the Hubble constant essentially tells us how old the universe is and how big it is, so fundamentally crucial to our understanding of the universe around us now is this debate over whether it was 100 or 50. were finally resolved by this wonderful instrument, the Hubble Space Telescope, launched in the early 1990s. Now Hubble was used to conduct a wide-range study of the observed stars, so here is a beautiful photograph of a uh sepid taken by the Hubble space telescopes. get these really beautiful measurements of these pulsating stars and this will allow you to make more precise distance measurements, but what Hubble also allowed astronomers to do was extend the distance scale even further out into the universe.

There comes a point where you're looking at galaxies. which are so remote that you can't resolve individual seids, so to measure their distances you need a different sail that we call standard, so here's essentially how it's done, so this is a diagram that represents what we call the ladder of cosmic distance. There are three rungs on this ladder, the first is, it uses a technique known as Parallax, so we can essentially use this to measure distances to things in our local galactic neighborhood. Now, Parala may sound fancy and mathematical, but it's what we all use to judge distances.

If we have two eyes, you basically know that the way we judge distances is that our two eyes have slightly different points of view and that means that objects appear slightly different in the two images and that allows us to create a kind of model 3D. of the world now our eyes are too close together to be able to notice the differences between the different stars, but the Earth orbits the sun and with periods of 6 months apart there are 300 million light, so there are no light years at 300 million kilometers away and that gives you a long baseline, you can essentially use it to see how the stars move in the sky and get a measure of the distance, then you use seids which allow you to measure distances up to about 100 million uh years light, but then beyond that you use another object known as a type 1A supernova, so this is a photograph of the galaxy NGC 2525.

I hope I understood that correctly. This was a supernova that exploded in 1994, so it's actually a photograph taken by Hubble. See the spiral galaxy and then this little dot here is the type 1A supernova. This is essentially the dead shell of a Sun-like star that violently detonates and briefly eclipses the entire galaxy, and it is believed that basically all types explode with a similar brightness. so if you can calibrate how bright they are and you can see these things incredibly far away because they're so bright, you can use them again to measure the distance, so Hubble made these new measurements seids uh and and uh and typon supern noi and got a new measurement of the Hubble constant, wow, a daisy, um, and it came out at 72 give or take 8, so neither 100 nor 50, they were both wrong, it was actually somewhere in between, which is maybe not entirely surprising , so in 2001 the Hubble key project had completed its work the debate over the Hubble constant was done and dusted you know why you would bother measuring it again we know the age of the universe we know how big it is we might as well go home but then something happened Then, in 2013, this lovely instrument, which is the Plank spacecraft launched by the European Space Agency, produced its first results.

Now Plank is a very special spaceship. I wasn't looking at stars or galaxies, I was looking at the Big Bang itself. Plank made a study of what we know as the cosmic microwave background. This is the fading light from the Big Bang itself and it produced, essentially, if you think about what we see when we look out into the universe, this is a sort of diagram that represents the observable universe we're in the middle of, although we're not actually in the middle of the universe, it just looks like this from where we are, um and since light travels at a finite speed, the farther away you look, the further back in time you look, as you go through this image, you see the Sun in the middle and the planets, then you see the Milky Way and then the distant galaxies and then as you go further and further, you eventually see this dark band that is essentially a time before the first one.

Stars formed, but if you keep looking, you'll look back enough in time to see the primordial fireball that filled the universe from the beginning, now that would once have been a very, very bright radiant fireball, but because to the expansion of the universe. that light has spread to a very cold microwave signal known as The Cosmic Microwave Background and Table produced the most accurate map of this radiation ever created; essentially took a picture of the universe as it was about 38,000 years after it was born so this is the oldest picture we can get or sorry the youngest picture we can actually get of the universe now what you're seeing here these different Colors represent regions of the universe that were slightly hotter and denser than others, so the blue parts are a little emptier and a little colder, uh, the brighter yellow and red parts are a little hotter and a little denser now, these are very subtle temperature fluctuations, but by studying them you can get a treasure trove of information about the universe in particular, you can use this data to find out how much dark energy there was in the early Universe how much dark matter there was how much radiation how much ordinary matter and with that information you can plug it into Einstein's general theory of relativity and you can move the clock forward so that essentially you can You have this data from the early moments of the universe and then you can use it to predict how fast the universe should expand today, so you have these two different methods essentially for measuring the Hubble constant.

One is using galaxies and you measure it essentially. for things we can see each other, you look at the big bang and then predict what it should be, so in principle if your cosmological theory is correct you should get the same answer, but when Plank published his result he disagreed , so they get a value. of 67 plus or minus 1.2 when this result and at this point the Hubble measurement had been updated by another team that had reduced the error substantially, so now you had these two numbers that are in really noticeable tension with each other now . It led to a lot of scrutiny, particularly for the team that had used the Hubble Space Telescope because people basically said, "You got it wrong, you misunderstood Sephi, you measured distances wrong, and you basically spent the last decade delving into his methods." repeating the measurements again and again with more data from more telescopes to confirm this measurement of the Hubble constant and this Hubble tension, as it is known, became a kind of real crisis in some sense in a CO in cosmology.

So how can you have two different measurements of the expansion of the universe give you different answers? Well, once again, as I said before, there are always boring explanations. One boring explanation is that we don't know how to measure distances, for example, but an exciting explanation is that something profound is missing from our understanding of the universe. Perhaps the standard cosmological model is incomplete. Something is missing in this image. This would not be very surprising if you consider that another name for the stand cosmological model is the Lambda CDM model. Lambda means dark energy and CDM means cold Dark Matter, so the two things that dominate your theory of the universe are completely unknown, so maybe it wouldn't surprise you if there was something else you haven't seen, so the Hubble strain . could be the key to something new we don't understand about the history of the universe and that's why it became so wildly exciting that the problem was ultimately that the debate over the Hubble tension came down to people not really trusting it. distance measurements. based on these sephi stars and as I said before, the cosmic distance ladder basically relies on these seids to act as a bridge between the things we can measure in our local galactic environment and much more distant things in the very, very distant Universe .

If that middle rung falters, then the entire ladder could essentially collapse, so the question was: can we really trust these timid stars? The reason why people maybe suspected these stars is that, because they are young stars, kind of pulsating, they form in the star-forming dust Lanes of spiral galaxies, so here we can see a really picture beautiful of NGC 5468, which is actually the most distant galaxy in which we can resolve individual seiad stars. I think it's about 130 million light years away, so these seads live in these dust-forming regions and if you have dust that can block the light from the sepids and that makes them appear dimmer or redder than they look. they really are and that can lead you to misestimate the size of the universe, which everyone has been waiting for.

With great anticipation to solve or help solve this puzzle, it's a beautiful thing, so this is the James Web Space Telescope or at least when it was being built here on Earth, it is in a sense the kind of spiritual successor to the Hubble Space Telescope . It was decades in the making of this incredible, vast, gold-colored mirror and James Webb's job is essentially to look at the universe, but unlike Hubble, which primarily looked at the universe in the invisible light of the optical spectrum, James Webb looks at the universe. in infrared, that's the key, so here we can see the Webb launch, this was launched on Christmas Day 2021, which is real, I think it's a real moment, you know, squeaky, as people say in science or also in other fields where you have this incredible multi-billion pound instrument on top of a massive bomb that's essentially being launched into space, but it's amazing that everything went off without a hitch.

The network made its way to a very distant range point from Earth and this incredible deployment unfolded. mirror and its solar shield and has been making beautiful observations of the heavens ever since and here is one of the results of the U observations from the web here is that same galaxy uh NGC 5468 again, but this time superimposed on the visible light measurement of the Hubble infrared measured by the web and when the team that was measuring the Hubble constant reran their analysis using this new data from James's web, their number, the Hubble constant number landed in the same place, for So this eliminates one of the main challenges to really believing that the Hubble strain is actually an anomaly that is showing us the way to a new understanding, which is why we are now in this incredibly exciting moment.

In fact, I think there have been a lot of skeptics about this particular anomaly over the years and not all of them are. I'm convinced, but I think more and more, as I talk to cosmologists, they're more and more convinced that there really is something we don't understand about the universe. So what could this mean? One of the reasons it took so long for the Hubble strain to be accepted is essentially there is no ready-made theoretical explanation for this. One of the driving figures behind this entire story is an astronomer named Adam Reese. Now Adam Reese became very famous as one of the co-discoverers in the late 1990s. the accelerated expansion of the universe, so he and a team and actually two different teams of astronomers discovered that galaxies are actually shrinking. accelerating in its expansion and this led to the realization that the universe is permeated with this thing we now call Dark Energy when I asked.

Do you know why you think accelerated expansion was accepted relatively quickly, while this weird thing with the Hubble constant hasn't been accepted? He basically said that back in the 1990s there was already a ready-made explanation for the accelerated expansion back in the past. When Einstein was developing his general theory of relativity, he actually added an additional term to his equations which he called the cosmological constant. Now the job of the cosmological constant was essentially to keep the universe from collapsing because what Einstein realized was that under gravity the universe should simplyimplode in on itself and yet it seems nice and stable and static, so he added this repulsive Antigravity Force to his equations to prevent the universe from falling in on itself now that Hubble discovered that the universe was expanding there.

There was no longer a need for Dark Energy because essentially the universe is getting bigger, so it is simply a kind of impulse that effectively drives it to continue getting bigger and bigger, you don't need this Repulsive Force, but when the acceleration of this expansion, so there was was this something already done Einstein's cosmological constant is reintroduced and in an instant explains the observations there was a theoretical explanation already done this time there is none um now I think it's me I think in some ways it's quite a way strange to look at science to say: I won't believe the data unless there is a ready-made theoretical explanation for something.

Ultimately, you know science is about the universe as we find it, so we can't really use our biases or our propositions to decide what. whether we include it or not, but it seems increasingly clear that if you want to explain this anomaly in the expansion of the universe, in reality there will not be a single solution, it may be a combination of different effects, so a very popular explanation is something known. as early Dark Energy, so it's a type of force that shaped the universe in its earliest history, a few hundred thousand years after the Big Bang, but then faded away in the later universe, but then perhaps combined with Dark Matter interacting with itself in the later Universe in even more profound ways.

Actually, one possible set of explanations is that Einstein's theory of relativity needs revision and we need a new theory of gravity, so we still don't know how this story will end. or how this anomaly is going to be resolved, but it's looking more and more likely that it's actually telling us something important about the universe that we don't understand, so I think it's tremendously exciting now that these are just two stories that I've covered. Lots of anomalies at work, the book actually covers five big stories that dominate particle physics and cosmology, for example, particles with impossible energies exploding beneath the Antarctic ice and neutrinos appearing unexpectedly in experiments with no explanation. apparent now with any anomaly the most likely explanation is, ultimately, the boring anomalies usually disappear are usually an experimental error or a theoretical calculation error or just a bit of bad luck, but occasionally they are the key to a profound new vision of the universe and that is why I find them so exciting and that is why I decided to tell this story tonight and in the book, so if you have enjoyed this lecture I encourage you to get a copy where you can read everything. about the anomalies that baffle physicists today and also how they have shaped our understanding of the universe in the past, thank you very much