STFC-RAL-Pickavance LT R22 G.02: Deep.
STFC-RAL-Pickavance LT R22 G.02: And if you go further, you get to the point when the universe becomes dense enough, because it's getting smaller as you go out. So remember, because of this spherical geometry.
STFC-RAL-Pickavance LT R22 G.02: As we look out, the universe is getting bigger and bigger, but after we cross the equator, it's getting smaller and smaller, and that is how we can reconcile the fact that the universe was small and dense in the past with what we see out in the sky.
STFC-RAL-Pickavance LT R22 G.02: This is non-include geometry.
STFC-RAL-Pickavance LT R22 G.02: And by the time we get to a retreat of 1,000, when the scale factor here was a thousand times smaller than today, the universe has got a thousand times hotter, and hot enough to ionize hydrogen, and therefore, after that, it's filled with the plasma, and light cannot come directly through there, it just random walks after leaving the initial singularity. But by the time it gets here, it is free to come to us.
STFC-RAL-Pickavance LT R22 G.02: And you can also see interesting things from this figure, such as that two photons, whose light cones just about intersect each other in the past similarity, are separated by about a degree on the sky.
STFC-RAL-Pickavance LT R22 G.02: So if I look at the microwave background, I should expect to see fluctuations on the scale of a degree, because that's the maximum size that can be causally connected by astrophysical processes. Anything beyond that would have to be an initial condition.
STFC-RAL-Pickavance LT R22 G.02: Now, I spent long enough on that plot, but it's important to kind of get that picture down, otherwise the rest is harder to make sense of.
STFC-RAL-Pickavance LT R22 G.02: Now, we have to, with this metric, construct the usual objects in Einstein's theory, the Riemann tensor, the scalar curvature, etc. All that's on the left-hand side, and we can relate that to the energy momentum tensor through Newton's constant, its passing voluativity.
STFC-RAL-Pickavance LT R22 G.02: Now, the interesting thing is this.
STFC-RAL-Pickavance LT R22 G.02: that, this keeps happening. Sorry, I think I need to move the pointer here, right?
STFC-RAL-Pickavance LT R22 G.02: Yes.
STFC-RAL-Pickavance LT R22 G.02: No? Yes.
STFC-RAL-Pickavance LT R22 G.02: So, these new and new run from 1 to 4.
STFC-RAL-Pickavance LT R22 G.02: So, you might think there are 16 equations.
STFC-RAL-Pickavance LT R22 G.02: But in fact, the energy-momentum tensor, all the tensors are symmetric.
STFC-RAL-Pickavance LT R22 G.02: Because, for example, the distance between me and you is the same as the distance from you to me, so there are only 10 independent equations. But thanks to the simplification afforded by this metric, they collapse into just one equation, which is called the Friedman-Lehmet equation, and that relates the rate of change of the scale factor with time, which is called the Hubble parameter.
STFC-RAL-Pickavance LT R22 G.02: In terms of the energy density of matter, the curvature of spatial sections.
STFC-RAL-Pickavance LT R22 G.02: and something called Lambda, which I'll come to in a sec.
STFC-RAL-Pickavance LT R22 G.02: So given this equation, I can relate it to the Hubble parameter at the present day, and parameterize these in terms of the fractional contributions made to the critical density here, by matter, by curvature, and by lambda. So I defined these three fractional contributions, omega matter, omega k, omega lambda, and basically, if I divide through by its square, I get a sum.
STFC-RAL-Pickavance LT R22 G.02: These three components sum up to one, and that is the essence of the standard cosmological model. It's a very simple sum rule with only three terms. Why? Because of the assumed homogeneity and isotropy, which means there are no other terms.
STFC-RAL-Pickavance LT R22 G.02: Now, what is this lambda? Well, there is a term on the left-hand side of the equation which is allowed because in general relativity, there is local coordinate invariance, and to reflect that, you're allowed to add any term, arbitrary number, multiplying the metric to the left-hand side.
STFC-RAL-Pickavance LT R22 G.02: However.
STFC-RAL-Pickavance LT R22 G.02: A bit later, in the 1930s, when it was realized that this energy momentum tensor, which was using… being used to describe non-reativistic particles, dust.
STFC-RAL-Pickavance LT R22 G.02: That it actually… that dust, those particles, are actually excitations of quantum fields, and quantum fields are zero-point energy.
STFC-RAL-Pickavance LT R22 G.02: And it turns out that that zero-point energy, because of the requirements of Lorentz invariance, it has… the vacuum has to be the same as seen by any observer.
STFC-RAL-Pickavance LT R22 G.02: it has also the same property as this cosmological constant on the left. It multiplies the metric.
STFC-RAL-Pickavance LT R22 G.02: So now you have two terms, one from the geometry and one from the arrangement of tensor, and they add up together to give what I have called here capital lambda, to distinguish it from the geometric lambda on the left-hand side.
STFC-RAL-Pickavance LT R22 G.02: And it is that capital lambda that enters the Friedman equation in terms of this omega lambda, which is lambda over 3 times H0 squared. H naught is the rate of expansion today.
STFC-RAL-Pickavance LT R22 G.02: And at this point, you should start, already start thinking about what this should entail when you start making observations, but I'll come to that in the next slide. I should say that this, energy momentum tensor, the vacuum energy.
STFC-RAL-Pickavance LT R22 G.02: It has to be, as I said, the same to every observer, and therefore its pressure has to be the negative of the energy density, because the energy momentum denser has to be diagonal. And what that means is that if I look at the second equation, the second equation is a simplification of what's called Rajo-Durie's equation.
STFC-RAL-Pickavance LT R22 G.02: the gravitating amount of matter in the universe is not just rho, but it is rho plus 3P, because P is pressure, it's kinetic energy, which also gravitates in Einstein's theory. And if P is minus of rho, then you can see this whole thing is going to be negative, and that
STFC-RAL-Pickavance LT R22 G.02: collaborates with this minus sign out here to make the acceleration of the scale factor positive. So you'd expect that in any universe with a lambda or vacuum energy, you would get acceleration.
STFC-RAL-Pickavance LT R22 G.02: And lo and behold, that's exactly what was found some years later. This was, as I like to say, an accident waiting to happen, because that is the structure of the model in which you're going to interpret data, and it already contains in it all the necessary ingredients to give us non-zero value of lambda.
STFC-RAL-Pickavance LT R22 G.02: So, we have data from the cosmic microwave background, from Type Ia supernovae, and from features in the correlation function of galaxy clustering, such as these little waves that you can see.
STFC-RAL-Pickavance LT R22 G.02: which are called baryon acoustic oscillations. They are exactly the analog of the oscillations that you see in the microwave background angular power spectrum, which are most prominent on a scale of 1 degree, as I pointed out earlier.
STFC-RAL-Pickavance LT R22 G.02: And, which… well, you can see the spots with your eye here. And, this tells us the position of this spot is, of these, features, is proportional to square root of omega k, so it tells us that omega K is close to zero from the microwave background.
STFC-RAL-Pickavance LT R22 G.02: The Type 1A supernovae gave us the difference between omega matter and omega lambda, this combination of these two quantities, right?
STFC-RAL-Pickavance LT R22 G.02: And, all these other measurements, like the baryon traction in clusters, BO, etc, they tell us that omega matter is something like 0.3.
STFC-RAL-Pickavance LT R22 G.02: So now if I put all these things together, then I have that omega lambda is 1 minus omega matter minus omega k is about 0.7. And if you remember what the definition of omega lambda was, lambda over 3H02, this means that lambda has a value set by the present-day Hubble parameter square.
STFC-RAL-Pickavance LT R22 G.02: Because I'm using the sum rule to derive it.
STFC-RAL-Pickavance LT R22 G.02: So it is neither fundamental nor a constant, but it is what determines lambda as I have defined it in this framework.
STFC-RAL-Pickavance LT R22 G.02: And this is usually shown on this so-called banana plots with omega lambda here, omega matter here. The condition that omega k is 0 is just the diagonal line that says that two add up to 1.
STFC-RAL-Pickavance LT R22 G.02: And the supernova constraint is orthogonal to it, and then you have the constraint from this matter, and they all coincide nicely at this point, and therefore you say that that is the standard model.
STFC-RAL-Pickavance LT R22 G.02: Except that…
STFC-RAL-Pickavance LT R22 G.02: From a fundamental point of view, this is having to buy the assertion that the universe is today dominated by a lambda of order H0 squared. H naught is 10 to the 28 centimeters, so in energy units it's 10 to the minus 42 GeV.
STFC-RAL-Pickavance LT R22 G.02: Not a scale that we have encountered in any fundamental theory. And…
STFC-RAL-Pickavance LT R22 G.02: the value of the energy density that is assigned to this is actually this lambda over 8 pi G, we write it in Planck units, to get it as a energy scale to the fourth power. And that turns out to be 10 to the minus 12 GeV, or 10 to the minus 3 electron volts.
STFC-RAL-Pickavance LT R22 G.02: Which is, not coincidentally, the temperature of the microwave background. This was all kind of put in by hands on the back.
STFC-RAL-Pickavance LT R22 G.02: But people often look at it and wonder how come you got such an interesting number. It's actually just the geometric mean of the Planck scale, which is 10 to the 19 GEV, and H naught, which is 10 to the minus 42 GE, right? These are the only fundamental scales in the problem. There are no other scales.
STFC-RAL-Pickavance LT R22 G.02: So, we have to now accept that we are
STFC-RAL-Pickavance LT R22 G.02: seeing a fundamental vacuum energy at a ridiculously small scale, nothing to do with any fundamental theory, and those of us who are concerned about this, then do wonder, are we inferring this simply because this is the only scale in the problem? It can't take on any other value.
STFC-RAL-Pickavance LT R22 G.02: And H0 is, of course, imprinted on every observation we make, because it sets the distance ladder, it enters into every cosmological data.
STFC-RAL-Pickavance LT R22 G.02: Now…
STFC-RAL-Pickavance LT R22 G.02: Some people at this point might be thinking to themselves, haven't I heard talks by lots of prominent people saying that the microwave background, the precision data from Planck, has established this model beyond doubt?
STFC-RAL-Pickavance LT R22 G.02: Well, here is the Planck data. These are the fluctuations mapped by Planck, and indeed, you get a nice fit to the fluctuations. And from that, they extract various parameters, which are listed in this table from the Planck paper. So you have the baryon density, which is the ratio of this to the bottom here. You have the cold dark matter density, which is the ratio of subsequent peaks. You have the optical depth to loss scattering. You have the, you know, lots of other parameters.
STFC-RAL-Pickavance LT R22 G.02: But my point is, I want you to show me where is the entry for lambda in this table.
STFC-RAL-Pickavance LT R22 G.02: There is no entry for lambda, because lambda is not actually measured by the CMB. Lambda at the time of CMB decoupling was… the redshift was 1,000, so the matchup density was 1000 cubed greater, but lambda was the same. So it was 10 to the minus 9.
STFC-RAL-Pickavance LT R22 G.02: It was a completely negligible effect on the baryonic acoustic oscillations that we see.
STFC-RAL-Pickavance LT R22 G.02: Now,
STFC-RAL-Pickavance LT R22 G.02: We infer lambda from the CMB by making measurements of omega matter and omega curvature. We don't actually measure it directly.
STFC-RAL-Pickavance LT R22 G.02: For the cognizante here, there are… it is, in principle possible to direct a very faint effect. So these fluctuations are above order 60 microK. The micro background temperature is 2.7 degrees K.
STFC-RAL-Pickavance LT R22 G.02: There is a very small correlation between the CMB and large-scale structure at the level of 0.5 microK, which is caused by lambda, but that has not yet been detected.
STFC-RAL-Pickavance LT R22 G.02: Now, very quickly, I'll remind you of what the expectation for lambda is in the Standard Model, just so that one can see how odd it is to infer it from possibility. So, of course, we all know and love the Standard Model, and we are now not so ambitious as to
STFC-RAL-Pickavance LT R22 G.02: say that it is everything there is. We accept it could be an effective field theory, valued up to some scale capital N, which is at least as high as 10TV, since we haven't found anything new at the LHC so far. And we know all about the gauge fields, we know about how the fermions couple to the Higgs field, we are in the process of trying to measure the Higgs potential at the LHC and so on.
STFC-RAL-Pickavance LT R22 G.02: And of course, we know that we can accumulate new physics into the standard model, like barrier number violation, or electron number violation, etc, by adding other terms which are damned by powers of the cutoff at which the new physics arises, so they can be naturally small. They'll decouple.
STFC-RAL-Pickavance LT R22 G.02: However, what people don't talk about much, because they're embarrassing, are two terms that you can add to the standard model Lagrangian, which are dimension less than 4.
STFC-RAL-Pickavance LT R22 G.02: And one of these is the notorious Higgs quadratic mass hierarchy problem, which is that the Higgs, if it is fundamental, will couple to everything in the vacuum, including, in particular, the top quark, which is actually heavier, and its mass correction from that coupling.
STFC-RAL-Pickavance LT R22 G.02: Diverges quadratically as the cutoff.
STFC-RAL-Pickavance LT R22 G.02: So, this is embarrassing because it's 125 GeV, and it ought to be a lot heavier if ME is higher.
STFC-RAL-Pickavance LT R22 G.02: Now, the way we attempt to solve that, as you all know, is either to argue that there is a whole set of superpartnered particles whose correction should be of opposite sign, and they would cancel that one and leave only a logarithmic correction, just as happens with the electron, whose divergence is canceled by the positron, and you have only a log correction log of M, which is
STFC-RAL-Pickavance LT R22 G.02: Small enough that it's under control.
STFC-RAL-Pickavance LT R22 G.02: But
STFC-RAL-Pickavance LT R22 G.02: That possibility has not, unfortunately, been realized yet, as far as you know. The other option is to make the Higgs composite, just like a pion, and then there is no quadratic evidence. But that also has not been so far seen in the data.
STFC-RAL-Pickavance LT R22 G.02: So, the first term here that I'm going to focus on in this talk is even more embarrassing, because that is the scale of the quantum fluctuations in the standard model.
STFC-RAL-Pickavance LT R22 G.02: Now, to be precise, we can't actually calculate vacuum energy, can only calculate differences in quantum field theory, not the absolute value, but the absolute value does double to gravity.
STFC-RAL-Pickavance LT R22 G.02: And order of magnitude, its case, should be afforded N to the fold, and what that means is that the expectation for this thing, however conservative you are, is at least 60 orders of magnitude higher than what the astronomers are telling us the vacuum energy is.
STFC-RAL-Pickavance LT R22 G.02: And what this means is that when the universe cools down from a high temperature, when you get down to a TV scale, at that point, the thermal energy is gone, the only thing that is left is vacuum energy, and if it really did gravitate, it should have sent the universe off into
STFC-RAL-Pickavance LT R22 G.02: Expansion forever, inflation. Or, if the sign of this thing is negative, it will re-collapse.
STFC-RAL-Pickavance LT R22 G.02: Actually, in QFT, we can't even calculate the sign.
STFC-RAL-Pickavance LT R22 G.02: So, if you read in astronomy textbooks that this is the biggest mistake in theoretical physics, or something as some distinguished colleagues have called it, it's complete nonsense, because we can't calculate it, so you can't predict it.
STFC-RAL-Pickavance LT R22 G.02: But, nevertheless, it is an embarrassment. It's a serious embarrassment, so when Paoli realized it, and Zeldovich back in the 30s, Paoli actually, said.
STFC-RAL-Pickavance LT R22 G.02: in the Handbook of physics, which I have looked up now, that,
STFC-RAL-Pickavance LT R22 G.02: I think it's gone again. Just one second.
STFC-RAL-Pickavance LT R22 G.02: Oh, yes.
STFC-RAL-Pickavance LT R22 G.02: Pauli writes in the Handbook of Physics,
STFC-RAL-Pickavance LT R22 G.02: As is obvious from experience, the zero-point energy does not produce any gravitational field. He was, of course, at the time, talking just about electromagnetism, but it holds bells on by the time you get up to other gauge fields.
STFC-RAL-Pickavance LT R22 G.02: So, this is not supposed to happen in general nativity.
STFC-RAL-Pickavance LT R22 G.02: So we don't understand why this vacuum energy should not couple to gravity, but that's the, you know, the statement is as given here. If it gravitated, we would not be here talking about it. And yet, because we brushed that problem under the carpet, because nobody has found a solution to this problem.
STFC-RAL-Pickavance LT R22 G.02: And because it doesn't affect anything you do in the lab, so, you know, it's reasonable that we should forget about it and get on with doing what we can do.
STFC-RAL-Pickavance LT R22 G.02: But that problem was still there, and it was waiting for the astronomers to come along years later and find lambda in their data, and then interpret it as vacuum energy, and then start this whole business of the standard cosmological model, without ever solving the original cosmological constant problem.
STFC-RAL-Pickavance LT R22 G.02: So I think I have said enough to indicate where I stand on this. I cannot believe that lambda can be of order H0 squared, and I think it must be an artifact.
STFC-RAL-Pickavance LT R22 G.02: So how do we proceed? Oh, I should mention that, you know, many of you like doing precision experiments, that people would expect some change in the theory of gravity at the spatial scale that corresponds to that energy scale of dark energy, which turns out to be about 100 microns.
STFC-RAL-Pickavance LT R22 G.02: And, people have been doing very elaborate Cavendish by Ballenstein experiments.
STFC-RAL-Pickavance LT R22 G.02: To try and see
STFC-RAL-Pickavance LT R22 G.02: if there's a departure from Neutronian gravity, you can, for example, parameterize it by some kind of a cow-like coupling with some coefficient under range, and here is the coefficient versus the range, and this is the scale where you would expect to see something happening.
STFC-RAL-Pickavance LT R22 G.02: But the coupling has already been limited to being below a tenth.
STFC-RAL-Pickavance LT R22 G.02: I think this is a few years ago, it has really gone down more by now. Basically, there is no indication for any change in the theory of gravity, as you might expect, if that dark energy is something to do with gravity.
STFC-RAL-Pickavance LT R22 G.02: Alright.
STFC-RAL-Pickavance LT R22 G.02: This, by the way, also applies to lots of mechanisms that have been suggested. Thousands of papers have been written suggesting that gravity is somehow screened by matter, and so on, so on. No evidence for any of that.
STFC-RAL-Pickavance LT R22 G.02: So why do we still believe in the Lambda CDM model?
STFC-RAL-Pickavance LT R22 G.02: Because it gives a nice description of the formation of large-scale structure in the universe, starting with those fluctuations that we saw imprinted on the CMB, which we ascribed to some prior period of inflation, although I should mention that Edward Harrison, who I referred to earlier, was at this lab.
STFC-RAL-Pickavance LT R22 G.02: Harrison and Zeldovich have a spectrum named after them, because they said, in order to create structure as we see it, we must have equal power of… in the fluctuations, in equal logarithmic intervals of wave number. And that Harrison-Zeldovich spectrum predates inflation by 30 years.
STFC-RAL-Pickavance LT R22 G.02: The reason why inflation became popular is because it naturally provides such a spectrum of fluctuations from a ruling scale of feed. But inflation is subject to the same cosmological constant problem that I've been moaning about for the last 15 minutes. So, you know, all this is basically make it up as you go along, because it all fits.
STFC-RAL-Pickavance LT R22 G.02: But… We'll have to yet determine if it is… any of it is correct.
STFC-RAL-Pickavance LT R22 G.02: But given those fluctuations, they can grow under gravity to create the structure today.
STFC-RAL-Pickavance LT R22 G.02: It just needs one new ingredient. You need about five times as much dark matter as ordinary matter, because otherwise the range in redshift from here to here is just thousand. The fluctuations grow proportional to the redshift, so they can only grow by a factor of a thousand, and they would not be strong enough to match what is seen on the sky.
STFC-RAL-Pickavance LT R22 G.02: So you need them to start growing before the universe had become transparent. And for that, you need some matter to support that growth, which doesn't interact with radiation.
STFC-RAL-Pickavance LT R22 G.02: So if you allow me six times as much dark matter as there is baryonic matter, and some mechanism that has created a Harrison Zelluvid spectrum of fluctuations, then I can describe the present universe. But that's not bad going, so you just need two new ingredients.
STFC-RAL-Pickavance LT R22 G.02: No…
STFC-RAL-Pickavance LT R22 G.02: At least from this point of view, we have accepted that we have some working model of how structure form.
STFC-RAL-Pickavance LT R22 G.02: And that the universe is inhomogeneous, and sure enough, if you map the universe, we are at the center of this picture. It is very inhomogeneous. This is a plot of the distribution of visible galaxies around us. We can't, of course, see the dark matter. And what is plotted here is the peculiar velocity.
STFC-RAL-Pickavance LT R22 G.02: So, there is a velocity proportional to distance, which is the Hubble expansion, but then you also have, because of the inhomogeneity, you have local velocities, which had nothing to do with Hubble expansion. For example, Andromeda is not even going away from us, it's falling towards us. It has a blue shift, not a red shift.
STFC-RAL-Pickavance LT R22 G.02: And that's because we are bound together in a dance that will end in 5 billion years.
STFC-RAL-Pickavance LT R22 G.02: These fine lines are measures of that velocity, which is plotted here, and this is also important, I should remark, that all measurements are typically made in velocity space, in redshift space. To transform to physical space, you need to know the scale, which is the Hubble parameter.
STFC-RAL-Pickavance LT R22 G.02: If you go out further, this is about 200 megaparsecs. Megaparsec is…
STFC-RAL-Pickavance LT R22 G.02: million parsecs, a parsec is 3.3 light years. If you go out to something like 700 megaparsecs, that is the biggest survey done, the Sloan Digital Sky Survey, and you see that web of galaxies you saw in the simulation, all that fits. But this raises various questions.
STFC-RAL-Pickavance LT R22 G.02: Are we justified in approximating this universe as homogeneous? Are we justified in assuming that we are at a typical point? Does it not matter if I'm in a dense region or in an empty region? Surely my past light code, on which my observations are coming, would be quite different in the two cases.
STFC-RAL-Pickavance LT R22 G.02: Does it not matter what direction I'm looking at? Because you can see, just from this picture, there's clearly a gross violation of isotropy.
STFC-RAL-Pickavance LT R22 G.02: Now, we have to make measurements in order to test these ideas, because these questions are not asked in the literature.
STFC-RAL-Pickavance LT R22 G.02: Now, we are flowing towards this supercluster called Shapley, and the idea is that that's because there's some big lump of matter that is pulling us. If that is the case, then our velocity should drop off as roughly 1 over R as we average over larger and larger volumes, and it should basically go to close to zero when we get to the scale of homogeneity.
STFC-RAL-Pickavance LT R22 G.02: Which, in the standard model, is around a couple of hundred megaparsecs.
STFC-RAL-Pickavance LT R22 G.02: Shapley is at about 160 megaparces.
STFC-RAL-Pickavance LT R22 G.02: So… Is our peculiar velocity falling off as 1 by R?
STFC-RAL-Pickavance LT R22 G.02: Well…
STFC-RAL-Pickavance LT R22 G.02: We do know that we have a peculiar velocity, because when you look at the cosmic microwave background, we see this evening sort of figure, which is what you expect. If you're an inertial observer moving through a isotropic radiation block at some velocity, this temperature difference is about a millik.
STFC-RAL-Pickavance LT R22 G.02: So that means your velocities also of order 10 to the minus 3 of C, and in fact, this was predicted by Stuart and Sharma, because they knew that we have a peculiar velocity, and it was indeed found, and Peebles and Wilkinson gave that formula for how the temperature should vary on the sky, which is today a special relativity exercise for
STFC-RAL-Pickavance LT R22 G.02: Undergraduates.
STFC-RAL-Pickavance LT R22 G.02: But in fact, we are not moving at, just 370 kilometers per second, which this indicates. We are actually moving at twice that speed, but as it happens, we are all… because we are moving backwards in the galaxy, we are also orbiting around the center in the opposite direction to this red spot, therefore half of that velocity is canceled out.
STFC-RAL-Pickavance LT R22 G.02: So our real motion is 620 kilometers per second, which is shared by the local group of galaxies, including Andromeda, as it shows here, and we are all moving towards what was called the Great Attractor.
STFC-RAL-Pickavance LT R22 G.02: So the game is to find the great attractor, which, I'll give you the spoiler alert, has never been found, and nevertheless, we persist in
STFC-RAL-Pickavance LT R22 G.02: analyzing old data according to this model, in which you should converse to the frame, in which the microwave background is isotropic, by averaging on scales larger than about a hundred over H megaparsecs. All distances are… have this H inverse, because that is a quantity that determines the physical scale related to the redshift scale.
STFC-RAL-Pickavance LT R22 G.02: So, do we, in fact, converse to the CMB frame by doing averaging? Well, here is a plot of all the data accumulated in the last 40 years, showing the bulk flow, our local velocity, as a function of the averaging radius.
STFC-RAL-Pickavance LT R22 G.02: So, there are some technical details you have to say, whether you're averaging on a top hat or a Gaussian, etc. Never mind. The point is that this purple line is the expectation from the standard model, and these are the data.
STFC-RAL-Pickavance LT R22 G.02: So, locally, things seem to be nicely consistent, but as you go further out, the C11 was actually our work, using Type 1A subunruvate. It seems to be getting discrepant at least the, you know, one sigma level.
STFC-RAL-Pickavance LT R22 G.02: The uncertainties are large, because these… data points.
STFC-RAL-Pickavance LT R22 G.02: To determine the distance of these objects, you can't rely on the redshift. You have to have a direct measure of the distance, and that's very rare, very hard to combine cosmology.
STFC-RAL-Pickavance LT R22 G.02: You have to use some empirical relation. There's one called the Tully-Fisher, which is a correlation between the rate at which a spiral galaxy is spinning and its absolute brightness. And there is a similar thing for elliptical galaxies between the velocity dispersion and the brightness, called the fundamental plane.
STFC-RAL-Pickavance LT R22 G.02: You use those indicators, they're only good to about 15-20% to get these, so there are actually large horizontal error bars also on these things, which is why people haven't been taking this seriously.
STFC-RAL-Pickavance LT R22 G.02: Until quite recently, two sets of, authors
STFC-RAL-Pickavance LT R22 G.02: have now measured this bulk flow, especially from the Cosmic Flows 4 survey. The picture I showed you was Cosmic Flows 3. The latest survey, they find that the bulk flow, if anything, is now definitely not falling. It is, if anything, rises
STFC-RAL-Pickavance LT R22 G.02: And, the remark that they make in their paper is that this is in tension with the standard model at something like, I don't know, 4.56 sigma, something like that, right?
STFC-RAL-Pickavance LT R22 G.02: So this is nevertheless, while interesting, not definitive, not just because of the sigmas, but because of the systematic uncertainties that people know are associated with this distance measure.
STFC-RAL-Pickavance LT R22 G.02: By the way, I should quickly say, although I'm running out of time rapidly, that if we are in a bulk flow, which is indicated here in this yellow region, and you calculate what a observer embedded in the bulk flow will see when they look at data from distant objects.
STFC-RAL-Pickavance LT R22 G.02: Then, according to Christoph Sagas, who is a relativist in Thessaloniki, if you… the blood flow is converging.
STFC-RAL-Pickavance LT R22 G.02: then you will have a correction term to the deceleration parameter, which is the rate of change of the Hubble parameter, which is of opposite side to the first one, and can cancel it out if that bulk flow is strong enough. And what that means is that even if the universe is globally decelerating, you might locally think of it as acceleration.
STFC-RAL-Pickavance LT R22 G.02: Now, when I met Christos, I heard his talk, and I said, can you calculate that term? And he said, well, you'll have to tell me the vorticity and shear of the local bulk flow, and I said, no, no one has measured that, but surely it will be in the direction that we are moving.
STFC-RAL-Pickavance LT R22 G.02: And he says, yes. So I said, in that case, the acceleration, if it is an artifact of this, should be only in the direction you are moving.
STFC-RAL-Pickavance LT R22 G.02: And he said, yes. I said, we can look for that in the data.
STFC-RAL-Pickavance LT R22 G.02: And we did.
STFC-RAL-Pickavance LT R22 G.02: We took a catalog of 740 supernovae, all analyzed using the same light curve template, etc, and we do a Taylor expansion of the luminosity distance, the brightness of the supernovae, in terms of the Hubble parameter, and the next quantity is the deceleration parameter, which is defined thus.
STFC-RAL-Pickavance LT R22 G.02: with a minus sign, because it was expected to be decelerating, but it turned out that the deceleration parameter is actually negative. It's wanting it to be positive. But what we see here is that it's actually very slightly negative.
STFC-RAL-Pickavance LT R22 G.02: But the dipole, if I allow that turb to have a monopole term and a dipole term, the dipole is 50 times bigger than the monopole. It's basically a dipole.
STFC-RAL-Pickavance LT R22 G.02: There is a tiny monopole term consistent with 0 at 1.4 sigma.
STFC-RAL-Pickavance LT R22 G.02: So, in fact, Christos was right. The acceleration is in the direction that we are moving.
STFC-RAL-Pickavance LT R22 G.02: It is not in isotropic, as it should be if it was due to lava.
STFC-RAL-Pickavance LT R22 G.02: Now, this was, of course, highly contested, because it obviously directly disproves the existence of lambda, and we thought, as a matter of interest, you'd go back and look at the supernovae that the two teams that got the Nobel Prize for the discovery of processing acceleration looked at.
STFC-RAL-Pickavance LT R22 G.02: Interestingly, they looked at only about 50 or 60 each, and most of them are in the direction of our bulk roof. They did not have telescopes at the time with which to look at the other part of the sky.
STFC-RAL-Pickavance LT R22 G.02: And then one of them complained that we had looked at a old catalog. The 740 was from 2014.
STFC-RAL-Pickavance LT R22 G.02: Actually, he was the author of the catalog, but never mind. Now we have a new catalogue of
STFC-RAL-Pickavance LT R22 G.02: twice that number, and you can see the redshift distribution here, and we see the same pattern. We see a strong dipole, which is decaying away on a length scale of a few hundred megaparsics. So, that is exactly how we'd expect a bulk flow to behave.
STFC-RAL-Pickavance LT R22 G.02: And everything seems to fit with the idea that we have local anisotropic acceleration, only up to a few hundred megaparsecs. Beyond that point, we don't really know because there is no data, but there's data soon coming from the Rubin telescope.
STFC-RAL-Pickavance LT R22 G.02: So now let me, in the remaining 8 minutes, 10 minutes, get on to my actual topic, which is the isotropy of the universe. Now, this is a picture from
STFC-RAL-Pickavance LT R22 G.02: Piebel says textbook, which says, this picture shows the radio sources mapped from, Green Bank, West Virginia, and it shows that the universe is isotropic.
STFC-RAL-Pickavance LT R22 G.02: So for a long time, I wondered what that, you know, you see this little streak here? I wondered what that was. That's actually our galaxy, because there are radio sources in our galaxy.
STFC-RAL-Pickavance LT R22 G.02: And these, blank regions.
STFC-RAL-Pickavance LT R22 G.02: are the bits you can't see from West Virginia.
STFC-RAL-Pickavance LT R22 G.02: Now…
STFC-RAL-Pickavance LT R22 G.02: The statement that this shows the isotropy of the universe cannot be correct, because if the microwave background is showing a distinct dipole anisotropy, then so should this.
STFC-RAL-Pickavance LT R22 G.02: Why can't we see it? Because there are only 30,000 sources here.
STFC-RAL-Pickavance LT R22 G.02: You want to look for the effect of one part in 10 to the three. You need at least a million sources, and that was lacking in the old days. But the reason why we are so sure we should see it is because it is an effect called aberration.
STFC-RAL-Pickavance LT R22 G.02: Which was actually discovered a couple of hundred years before the theory of special relativity by Bradley, who was the civilian chair of astronomy at Oxford. And he, in fact, discovered it and gave a formula for it, which is the special relativistic formula, long before special relativity.
STFC-RAL-Pickavance LT R22 G.02: What he observed was that a star is displaced on the sky in the direction of our motion. And, in fact, this tells you the ratio of the velocity of the, our motion
STFC-RAL-Pickavance LT R22 G.02: relative to that of light, because Bradley correctly deduced this was due to the finite speed of light. And he estimated the speed of light to within one pers…
STFC-RAL-Pickavance LT R22 G.02: You know, amazing going in 1728, right?
STFC-RAL-Pickavance LT R22 G.02: Now, this, therefore, is for real. You can't avoid this aberration effect.
STFC-RAL-Pickavance LT R22 G.02: But, of course, for individual sources, you have to worry about, you know, what you're seeing. So, for example, if they have a power law spectrum, you're sampling a different part of the spectrum as a moving observer, and if the number distribution of sources is falling off as a power law on top of… according to the flux, then you have to take this into account as well. So, you're looking, maybe I should show a picture.
STFC-RAL-Pickavance LT R22 G.02: If I have a picture here of isotropically distributed sources, and if I'm moving in that direction towards that red point.
STFC-RAL-Pickavance LT R22 G.02: then I should see the sources bunched up around there, leaving a hole in this direction, because the sources which would have been below my flux threshold in a flux-imited survey will be boosted above it and reversed in the backward direction, right? And
STFC-RAL-Pickavance LT R22 G.02: This was calculated by George Ellis and John Baldwin. John Baldwin was the head of the Millard Space Radio Astronomy Lab at Cavendish. They were about to undertake the Cavendish Survey of Radio Sources, and George Ellis is a radiivist from South Africa.
STFC-RAL-Pickavance LT R22 G.02: And they pointed out that V over C cos theta, which you saw for the CMB, has to be multiplied by a small factor, which adds up to about 5. It boosts the signal by a factor of 5, according to these indices alpha and X, which are the power law indices of these objects.
STFC-RAL-Pickavance LT R22 G.02: So, this is Ellison Baldwin's original paper.
STFC-RAL-Pickavance LT R22 G.02: written, as you see, at the Orthodox Academia of Crete. I don't know if any of you have been there, it's a lovely place right on the beach. So I can just imagine Ellison Baldwin chatting about this at 2 in the morning, over a glass of resin or two, and saying, you know, we have found a consistency test of the FLRW metric, because
STFC-RAL-Pickavance LT R22 G.02: if the…
STFC-RAL-Pickavance LT R22 G.02: macroe background and the number counts, the dipoles, that is, were to be in serious disagreement, then one would have to abandon the standard FLRW universe models if the radio sources are indeed cosmologically distant, and the interpretation of the CMB as primordial is true.
STFC-RAL-Pickavance LT R22 G.02: So, let me go a bit quickly, because I don't want to keep you beyond… I know we are all waiting for lunch.
STFC-RAL-Pickavance LT R22 G.02: So, we got data from this catalog, created by a satellite called WISE, an infrared satellite, which orbited for many years. In fact, it shut down only a couple of months ago, finally, and it surveyed the sky in four bands, all at a few micron wavelengths.
STFC-RAL-Pickavance LT R22 G.02: And if you do multiple bands, then you can do a color-color plot and isolate quasars from other kinds of stuff that you don't want. And of course, you can then examine them individually as to what the spectra is with some other instrument. WISE itself doesn't have spectroscopy. And by doing so, we created a CAT.
STFC-RAL-Pickavance LT R22 G.02: catalog.
STFC-RAL-Pickavance LT R22 G.02: of about 1.5 million quasars, you have to make sure that they are complete down to some flux limit. So, these checks were done. You have to also check that there are no systematics associated with the orbit or the scanning pattern, and in fact, we found a 1% drift in the number counts with the angle, which is
STFC-RAL-Pickavance LT R22 G.02: usually involved in these things called the ecliptic, because we are orbiting in the ecliptic, so you tend to see anything associated with that. So we correct for all those things, and we create a map of the sky.
STFC-RAL-Pickavance LT R22 G.02: which has got about 1.4 million quasars, and we are lucky to get these, because our first author, Nathan Seacrest, he's at the Naval Observatory in Washington, and he sits on the committee that actually maintains the reference frame with… for satellite navigation, for which they use quasars. So they are really meticulous people, they have to be.
STFC-RAL-Pickavance LT R22 G.02: And my other collaborators are Mahmoud Ramiz, who is at the Tata Institute in Bombay, Sebastian von Hausiger, who is a postdoc in Oxford, and Roya Mohai, she's a relivist and cosmologist at the Institute of Astrophysics in Paris.
STFC-RAL-Pickavance LT R22 G.02: So, our lucky break was that these quasars, some of them had their redshifts measured by the Sloan Digital Sky Survey, and that told us that they're indeed at cosmological distances. The mean redshift, as you see, is more than one.
STFC-RAL-Pickavance LT R22 G.02: And when we smooth this map, we see the expected dipole pattern, right? And we see the hot spot and the cold spot, and now we can create mock skies by sampling from the distribution of spectral indices
STFC-RAL-Pickavance LT R22 G.02: and flux indesis for these, and I should say that Wilbur was kind enough to help us on our first paper, keep us honest when we did this. So we generated 10 million mock skies, and asked, what is the expected diver you should see? And that is that hill here.
STFC-RAL-Pickavance LT R22 G.02: And, what we find is that the direction of this dipole is consistent with the direction of the CNB dipole to within the uncertainty.
STFC-RAL-Pickavance LT R22 G.02: But its magnitude is way out.
STFC-RAL-Pickavance LT R22 G.02: Okay? Out of the 10 million simulations, only 5 made it up to the point that we observed. So the p-value is transparently 5 times 10 to the minus 7, which is 4.9 sigma for a one-sided Gaussian, right? We did a frequentist analyst, because that's what I like. It's transparent, it's simple, there's no hand-wearing going on, but of course, we have now created the Bayesian estimate
STFC-RAL-Pickavance LT R22 G.02: Like everybody else.
STFC-RAL-Pickavance LT R22 G.02: I should point out that this dipole is also seen in the catalog of radio sources from the Very Large Array, the NVSS catalog, and that that has got less. After you mask out the galaxy, etc, then there are less sources, so… but the directions are consistent, and the velocity is consistent.
STFC-RAL-Pickavance LT R22 G.02: And in fact, since these two catalogs, the NVSS catalog and the Weiss catalog, are totally independent, I should say that NVSS is looking at radio sources, which are basically the jets of plasma being ejected from the central black hole and creating huge radio lobes, whereas
STFC-RAL-Pickavance LT R22 G.02: WISE is looking at the central engine, which is shouted by accretion disk, and that heats up and emits infrared, and that is what we see in the WISE satellite.
STFC-RAL-Pickavance LT R22 G.02: So, that…
STFC-RAL-Pickavance LT R22 G.02: although they're both powered by black holes, the surveys are independent and pick out different objects. In fact, there were 50 objects in common in the two catalogs. We, of course, removed them, and then we have two independent measurements, and we can combine them, and we get more than 5 sigma. Other people have checked our results, they find even stronger significance in the Bayesian analysis.
STFC-RAL-Pickavance LT R22 G.02: And now, very recently, there's a PRL by people from Billfield, and they have over 5 sigma from radio data alone.
STFC-RAL-Pickavance LT R22 G.02: So, it seems to be that this is being confirmed independently using radio sources which are mapped from the ground, and satellites, which, of course, do it from the sky, and which therefore are very different systematics. They're seeing the same result. So, at least we are pretty confident that it's for real.
STFC-RAL-Pickavance LT R22 G.02: Okay, I'll skip this for lack of time. This is because some people started saying, why are you using special relativity? You should use general relativity. And the bottom line is, if you use general relativity, then we get back the Ellis Baldwin formula plus a correction, which turns out to be about
STFC-RAL-Pickavance LT R22 G.02: 10 to the minus 4. So, you know, Ellis and Baldwin were quite right.
STFC-RAL-Pickavance LT R22 G.02: And there is no issue with the… I mean, the fact that it's a three-dimensional universe is not relevant, because what you are seeing projected onto the sky contains all that information about the evolution and so on. So that's one way to look at.
STFC-RAL-Pickavance LT R22 G.02: So this is the bottom line.
STFC-RAL-Pickavance LT R22 G.02: We now have this anomalous dipole in at least 3 different samples. It is consistent in direction with the CMB dipole, but not consistent in the amplitude. We have, of course, done various systematic checks to see that the dipole is stable with the magnitude cut. The direction does drift, but not the magnitude.
STFC-RAL-Pickavance LT R22 G.02: And very recently, this is a paper about to come out in monthly notices. We have constructed the angular power spectrum of this catalog, and at small scales, it matches what you expect for structure formation in CDN, as one might expect. So we can then extrapolate that to L of 2 and read off the
STFC-RAL-Pickavance LT R22 G.02: What sort of a dipole might there be on the sky from clustering?
STFC-RAL-Pickavance LT R22 G.02: Which is something which is often invoked.
STFC-RAL-Pickavance LT R22 G.02: To try and account for our observation.
STFC-RAL-Pickavance LT R22 G.02: But you can see for yourself that this is what you expect from Lambda CDM, and this is what we are measuring, and there is quite a bit of clear water in between the two.
STFC-RAL-Pickavance LT R22 G.02: And, in fact, there is no other large-scale power. Other people had found large-scale power because they didn't clean up the map enough, but it is essentially like the CMB.
STFC-RAL-Pickavance LT R22 G.02: So, what has the community said about this? Well, I thought I would quote Jim Peebles, who is the kind of doin of our field.
STFC-RAL-Pickavance LT R22 G.02: And he says this anomaly is as well established as the Hubble parameter as the Hubble tension, yet the literature on it is much smaller than the hundreds of papers about the Hubble tension. I expect the difference is an inevitable consequence of the way we behave. I have no idea what he means by this.
STFC-RAL-Pickavance LT R22 G.02: However, the problem is the following.
STFC-RAL-Pickavance LT R22 G.02: That this is not something that you can just tweak a model and write a, you know, toss off a theory paper about. It does mean going back to square one.
STFC-RAL-Pickavance LT R22 G.02: And so, although there has been a fair bit of interest from the theory community, it is fair to say we have neither they nor we have any alternative to put in the place of the standard cosmological model.
STFC-RAL-Pickavance LT R22 G.02: And for that reason, it has been largely ignored, and I thank you for having the patience to listen to the evidence, which is just come out of the fact that this model was constructed back in 1922 by Alexander Friedman.
STFC-RAL-Pickavance LT R22 G.02: And he didn't have any data. In 2022, we didn't even know that we lived in a galaxy. We didn't even know about the Hubble expansion.
STFC-RAL-Pickavance LT R22 G.02: Now that we have data, we should be doing these cross-checks. And yet.
STFC-RAL-Pickavance LT R22 G.02: The most recent sets of data, for example, from the Dark Energy Spectroscopic Instrument, DAISI, which is at, run by Berkeley, out of a satellite, telescope at Kid Peak.
STFC-RAL-Pickavance LT R22 G.02: They analyze all their data, assuming FLRW.
STFC-RAL-Pickavance LT R22 G.02: The dark energy survey that has just finished its 5- or 6-year mission does the same. Everybody continues to assume something for which now we have five sigma evidence demonstrating that it is not the case.
STFC-RAL-Pickavance LT R22 G.02: More interestingly, the inferred acceleration is also in the same direction, and therefore cannot be due to lambda.
STFC-RAL-Pickavance LT R22 G.02: This is more serious, because it means that we can't assume the fundamental metric that is used for space-time.
STFC-RAL-Pickavance LT R22 G.02: And departing from this situation of symmetry is asking for trouble, because Einstein's equations are very hard to solve, and you proliferate the number of parameters if you go away from this situation, and the data has not been there until today to address with such a more complicated model.
STFC-RAL-Pickavance LT R22 G.02: But now that data is coming, there is the legacy survey of space and time about to start on the Rubin telescope, in which there is strong UK involvement. There is nuclear satellite up in space.
STFC-RAL-Pickavance LT R22 G.02: The successor to WISE, called CRX, which you probably haven't heard so much about, was launched by Caltech last April. It's already done a survey of the sky, and that maps the sky in the same bands, or more or less, as WISE. So, very soon, not 10 years from now, 2 years from now, we'll know whether any of this is true.
STFC-RAL-Pickavance LT R22 G.02: Now, that data will represent a data challenge. So now you're talking about petabytes of data, and maybe to construct a cosmological model now, we can go trendy, and like everybody else is doing, start using machine learning to try to
STFC-RAL-Pickavance LT R22 G.02: To interrogate that data in order to construct the cosmological model directly from the data, rather than make a philosophical assumption and then test it.
STFC-RAL-Pickavance LT R22 G.02: So, I think I will end there. If any of you want to know more about the philosophy behind this approach to cosmology, I did write a popular-level talk. Popular meaning it does have equations, but it's not technical, which you are very welcome to look at. It's online and it's free.
STFC-RAL-Pickavance LT R22 G.02: Thank you.
STFC-RAL-Pickavance LT R22 G.02: Beautiful.
STFC-RAL-Pickavance LT R22 G.02: Sorry for going over time. Question from Room?
STFC-RAL-Pickavance LT R22 G.02: Yeah, well…
STFC-RAL-Pickavance LT R22 G.02: Fantastic talk, actually, and opens up many questions. I remember you talking in the past about Taiwan supernova not being the same everywhere. Is that… is that correct, or is there something… Yes, that is still true. So, what is done is that,
STFC-RAL-Pickavance LT R22 G.02: They are standardizable candles. So, basically, the intrinsic magnitudes vary by a factor of 10. This has been known all long. But,
STFC-RAL-Pickavance LT R22 G.02: it was found that, once you had CCD cameras to scan the sky, you could actually, when a supernova went off, you could go back and look at how much light you were getting from that direction two weeks earlier.
STFC-RAL-Pickavance LT R22 G.02: Right? So you could actually construct the whole rise chart, and then it was realized that the width of the light curve, so it rises and then falls, right? The width correlates with the absolute magnitude.
STFC-RAL-Pickavance LT R22 G.02: So this is called the Phillips relation, and using this, you can then reduce the scatter from a factor of 10 to less than a factor of 2, and then they can be used as standard candles.
STFC-RAL-Pickavance LT R22 G.02: But of course.
STFC-RAL-Pickavance LT R22 G.02: people keep finding other things that this absolute magnitude might correlate with. You know, might it correlate with the mass of the host galaxy? Might it correlate with some other property where the supernova is in it? So these are open questions. These are all empirical correlations. There's no theory behind them.
STFC-RAL-Pickavance LT R22 G.02: And…
STFC-RAL-Pickavance LT R22 G.02: Basically, the JLink catalog I showed you was done by taking four different surveys and analyzing all the supernovae with the same so-called spectral,
STFC-RAL-Pickavance LT R22 G.02: Salt. SALT stands for Spectral Adaptive Light Curve, and that's it. Salt 2.
STFC-RAL-Pickavance LT R22 G.02: So now we are on to salt 3, and no doubt we'll go on to Salt 4, but basically, that's how it is done.
STFC-RAL-Pickavance LT R22 G.02: Any questions from Rome?
STFC-RAL-Pickavance LT R22 G.02: Yep.
STFC-RAL-Pickavance LT R22 G.02: So, you probably know that the root telescope had quite some ups and downs in terms of the 3.2 gigapixels spoke later in, finally got it right, things in shape. I haven't actually heard… is it… is it now operating? Are they doing the survey regularly? No, the… it's about to… the survey is going to… about to begin, but I believe, you know, first light has been obtained, and
STFC-RAL-Pickavance LT R22 G.02: Get, like, 10 emails a day about how it's all going to be, and so on.
STFC-RAL-Pickavance LT R22 G.02: So, hopefully, it'll be on… but I believe it had to be scaled down, as you said, the original plan.
STFC-RAL-Pickavance LT R22 G.02: The thing is that,
STFC-RAL-Pickavance LT R22 G.02: If I may say so, it seemed to me that the telescope was built by particle physicists, and the data pipeline by particle physicists, but the people who will use it will be astronomers. Yes. And…
STFC-RAL-Pickavance LT R22 G.02: it would be important to ensure that the data analysis is done in a blinded way.
STFC-RAL-Pickavance LT R22 G.02: And not using the kind of circular logic that has been employed so far in cosmological analysis. And this might be somewhat hard to do.
STFC-RAL-Pickavance LT R22 G.02: But, yes. Particle physicists at Slack have had quite some problems with, negotiating, sort of thing, because it's… That's right, yes. Different styles of working each other. Sure, exactly, but LSST UK has got, almost every astronomy department in the UK involved.
STFC-RAL-Pickavance LT R22 G.02: And we are also… we have also joined it, because there's been a lot of service work done by the UK, so that, you know, people who haven't done actually anything for the telescope, like me, we can also join.
STFC-RAL-Pickavance LT R22 G.02: But we'll be able to, therefore, have access to the data.
STFC-RAL-Pickavance LT R22 G.02: For any questions from Zoom, please… Raise your hands.
STFC-RAL-Pickavance LT R22 G.02: Hi, this was a really incredible and informative thought.
STFC-RAL-Pickavance LT R22 G.02: I mean, I don't have a great understanding of cosmology, but…
STFC-RAL-Pickavance LT R22 G.02: Would we expect this allocated to be reflected in… when we try to study, like, bias and, like, direction of neutrinos that we receive as well?
STFC-RAL-Pickavance LT R22 G.02: Because, from what I understand, we've measured, like, biases in direction with respect to the sun for stellar… I mean, solar neutrinos, but would we also get a higher collection of neutrinos in the direction where we have the higher density as well?
STFC-RAL-Pickavance LT R22 G.02: So, to date, the total number of cosmic neutrinos we have detected is in the tenths.
STFC-RAL-Pickavance LT R22 G.02: That's not… like I said, you need, like, a million events to look for this kind of one part in a thousand, a few parts in a thousand, anisotropy. So you're a long way from doing that. But of course, for example, in IceCube, you do look for correlation of neutrinos with large-scale structure. Even that, so far, has not been proved definitively.
STFC-RAL-Pickavance LT R22 G.02: But you're right, that eventually any… anything that is generated cosmologically at sufficiently large distances should show the same anisotropy. Now, this is simply a consequence of our local motion.
STFC-RAL-Pickavance LT R22 G.02: So therefore, it imprints itself on everything, on the whole sky.
STFC-RAL-Pickavance LT R22 G.02: If we find, however, that the imprint is not the same in two different traces, right, that means that our fundamental assumption, in which we expect the two to be the same, mainly this assumption of isotropic homogeneity, something has to get there.
STFC-RAL-Pickavance LT R22 G.02: Unfortunately, it does not tell us what has to give, what is the weak point. That we can only determine by doing further observations. So, for example, with Rubin and also with SphereX,
STFC-RAL-Pickavance LT R22 G.02: We'll have spectroscopic data, so this million objects will be able to actually measure their spectra and red chips, and then we can do tomogram. So we can actually take shells of objects and trace out this dipole from locally out to wherever it's coming from.
STFC-RAL-Pickavance LT R22 G.02: And hopefully, that will then tell us something about the origin of it. So right now, there's a fair bit of speculation, but no hard data.
STFC-RAL-Pickavance LT R22 G.02: And I expect that, as I said, to happen within the next few years.
STFC-RAL-Pickavance LT R22 G.02: Which is just as well, because I can't wait 30. But this is… so, for example, there are a lot of activity along in the gravitational wave community as to what they might be able to see once they have, you know, millions of
STFC-RAL-Pickavance LT R22 G.02: Standard silence, which is the Blackwood Merges. But that's going to take a while.
STFC-RAL-Pickavance LT R22 G.02: The good news is that there is already data in the pipeline, and more data coming in the next 2-3 years, which is very relevant to
STFC-RAL-Pickavance LT R22 G.02: You know, checking, falsifying, if necessary, what you have found.
STFC-RAL-Pickavance LT R22 G.02: Thank you. Let's take a question from Zoom. Stefan, please unmute and go ahead.
Stephen Burke - STFC UKRI: Can you hear me?
STFC-RAL-Pickavance LT R22 G.02: Yes.
Stephen Burke - STFC UKRI: So you mentioned the Hubble tension, there's lots of attention on that. How does this interact with the Hubble tension? Could it explain it? Does it change it?
STFC-RAL-Pickavance LT R22 G.02: Yeah, I had a comment on a previous slide that, when we looked at the Pantheon plus catalog of supernovae, we found that there is also an anisotropy in the Hubble parameter.
STFC-RAL-Pickavance LT R22 G.02: So, that is to be expected in a homogeneous universe. You don't expect the Hubble parameter to be the same, expansion rate to be the same in every direction.
STFC-RAL-Pickavance LT R22 G.02: And therefore, the Hubble tension as it is posed is supposed to be a discrepancy between something called H0, which is an isotropic quantity, deduced from the microwave background, and that measured in the local universe today.
STFC-RAL-Pickavance LT R22 G.02: Now, the directions on the material background is fine, because once you subtract off this dipole, the remaining fluctuations are 140 and 100,000. The CMB is pretty isotropic.
STFC-RAL-Pickavance LT R22 G.02: But today, the universe is not isotropic, and therefore, if somebody claims to measure H0, I would have to ask them what direction you're measuring it in, because it's a bit like saying, you know, what's the radius of the Earth?
STFC-RAL-Pickavance LT R22 G.02: That question presupposes that the Earth is a sphere.
STFC-RAL-Pickavance LT R22 G.02: But the Earth is not a sphere, it's actually a geoid. It's got ups and downs, and, you know, these go up to 100, 200 kilometers. So you cannot measure the
STFC-RAL-Pickavance LT R22 G.02: radius of the Earth to within one person, because the Earth is not a sphere to their accuracy. So, think of the contours of the Hubble expansion similarly, and we need to map out those irregularities
STFC-RAL-Pickavance LT R22 G.02: before we can answer the question as to whether there is a hub retention. We certainly found evidence for anisotropy at a level higher than the clean precision of the measurement by the Schuss collaboration.
STFC-RAL-Pickavance LT R22 G.02: Just to follow up, if CMP is not, right?
STFC-RAL-Pickavance LT R22 G.02: film for the late universe, and what is? The CMP and matter were in thermal contact, right, before they decoup, so you would naturally expect them to have the
STFC-RAL-Pickavance LT R22 G.02: Share the same reference frame today.
STFC-RAL-Pickavance LT R22 G.02: If we are finding that the two don't match.
STFC-RAL-Pickavance LT R22 G.02: Then you have to find some way to distinguish photons from matter.
STFC-RAL-Pickavance LT R22 G.02: Now, that is hard to do, because under gravity, things fall at the same rate.
STFC-RAL-Pickavance LT R22 G.02: So, in particular, adiabatic… any fluctuations which is so-called adiabatic, which fluctuates matter and radiation together, is not going to cut it.
STFC-RAL-Pickavance LT R22 G.02: You could imagine that there is something called an isocurvature fluctuation, which is one in which, as it says, the curvature remains constant, but matter and radiation fluctuate opposite.
STFC-RAL-Pickavance LT R22 G.02: Thereby keeping the curvature the same.
STFC-RAL-Pickavance LT R22 G.02: And in fact.
STFC-RAL-Pickavance LT R22 G.02: Jim Gunn, who is an astronomer at Princeton, he had suggested quite some years ago, in the 90s, that there could be a giant isocurvature perturbation on the scale of the present horizon of the universe, which can affect
STFC-RAL-Pickavance LT R22 G.02: You know, creates as it distributes.
STFC-RAL-Pickavance LT R22 G.02: That is possible, but then it seems to require some fine-tuning, because if the CMB dipole is due to our motion.
STFC-RAL-Pickavance LT R22 G.02: And then something else is creating the matter dipole, why should the two be aligned?
STFC-RAL-Pickavance LT R22 G.02: Right? Now, it's true, they're not perfectly aligned, they're aligned within 20-30 degrees, so, you know, there is a few percent chance of getting that alignment by chance, but…
STFC-RAL-Pickavance LT R22 G.02: not a satisfactory thing. You'd want some more, you know.
STFC-RAL-Pickavance LT R22 G.02: Sort of better reason for why this discrepancy is arising.
STFC-RAL-Pickavance LT R22 G.02: as I said, all these questions currently cannot be answered, they need more data, but most importantly, they need people other than our small group to work on it, right? Because if we really have to go back to square one, that is going to take a lot more than
STFC-RAL-Pickavance LT R22 G.02: Just pointing out that there's something wrong.
STFC-RAL-Pickavance LT R22 G.02: In Denmark.
STFC-RAL-Pickavance LT R22 G.02: Okay, so if there are no other questions, then please let's thank our speaker.
STFC-RAL-Pickavance LT R22 G.02: Sorry, there is well over 10.
STFC-RAL-Pickavance LT R22 G.02: I think I need to… Let's close this thing.
STFC-RAL-Pickavance LT R22 G.02: Let's go.
STFC-RAL-Pickavance LT R22 G.02: Do you have to go to square one? Can't you do some sort of effective theory, where you say, put on some, you know, some viral germs on top of it, and see what they can do? Yes, indeed. One can, in fact.
STFC-RAL-Pickavance LT R22 G.02: construct a universe with one axis, this direction, and sort of expand around that. And people have tried doing that, but then you ask where that axis should come from, right? Why is there a particular axis? Oh, sorry, there are lots of messages in the chat. Yeah, I mean, I was checking them all, so it's okay. But do you have a record of them? Yeah, okay, then if you would say.
STFC-RAL-Pickavance LT R22 G.02: Okay, sorry, are you joining us for lunch? Yes, please. Okay.
STFC-RAL-Pickavance LT R22 G.02: Let me just close this thing off. Will this be visible on the web afterwards? Yes, we have a recording, we'll upload it, and then you go. Okay, good. Good to see you. Hi, hi.
STFC-RAL-Pickavance LT R22 G.02: How are you? I'm good, yeah, thanks.
STFC-RAL-Pickavance LT R22 G.02: Well, this keeps you busy. I'm so many things like that.
STFC-RAL-Pickavance LT R22 G.02: be a more professional.
STFC-RAL-Pickavance LT R22 G.02: It's like…
STFC-RAL-Pickavance LT R22 G.02: Anyway… Yeah, absolutely. It's like my standing bottle, right?
STFC-RAL-Pickavance LT R22 G.02: Is there a problem with reading something that costs too much.
STFC-RAL-Pickavance LT R22 G.02: fluctuations in the magic.
STFC-RAL-Pickavance LT R22 G.02: That's, like, the current standing model.
STFC-RAL-Pickavance LT R22 G.02: That is… otherwise… Otherwise, or create…
STFC-RAL-Pickavance LT R22 G.02: And that's actually consistent with the observations so far as we have.
STFC-RAL-Pickavance LT R22 G.02: We don't know. It certainly doesn't work. That object has been very subtle.
STFC-RAL-Pickavance LT R22 G.02: The problem is there's no data between 200 plus 6,
STFC-RAL-Pickavance LT R22 G.02: Do you have any, like, the best resources to learn more about, like, these items?
STFC-RAL-Pickavance LT R22 G.02: Something like poison out of it.
STFC-RAL-Pickavance LT R22 G.02: I suggest you start by… you'll find some references in the topic we like.
STFC-RAL-Pickavance LT R22 G.02: Yeah, and from that perspective… Well, there's… I mean, you could send it to me.
STFC-RAL-Pickavance LT R22 G.02: Nice way!
STFC-RAL-Pickavance LT R22 G.02: But you are right. That is all I'm going to get out of it.
STFC-RAL-Pickavance LT R22 G.02: But you should. You should, yeah.
STFC-RAL-Pickavance LT R22 G.02: Good! How's it? It's so cold, it's freezing.
STFC-RAL-Pickavance LT R22 G.02: Crazy!
STFC-RAL-Pickavance LT R22 G.02: I thought my forehead was going to fall off walking over.
STFC-RAL-Pickavance LT R22 G.02: Yeah, I mean, I was in Finland and China didn't fill anyone there.
STFC-RAL-Pickavance LT R22 G.02: I wish I brought my bobble hat now.
STFC-RAL-Pickavance LT R22 G.02: Here we are.
STFC-RAL-Pickavance LT R22 G.02: Great of a brush, so Laura is halfway to Souls picking up the LMT. That's okay.
STFC-RAL-Pickavance LT R22 G.02: I think Charlie's been in to switch it on, but he's not there, and he's the kind of person… I mean, we do need him.
STFC-RAL-Pickavance LT R22 G.02: We also had to do a sound test on a webinar as well, so I was just, like, debating whether I'd try that, but he's…
STFC-RAL-Pickavance LT R22 G.02: Again, we need him.
STFC-RAL-Pickavance LT R22 G.02: I couldn't grab too much.
STFC-RAL-Pickavance LT R22 G.02: I bought some flowers over. I bought a bunch of flowers. They're for you to keep, or smash. Up to you.
STFC-RAL-Pickavance LT R22 G.02: The rest of the flowers are in the kitchen in some water, we can use them Friday, but if you…
STFC-RAL-Pickavance LT R22 G.02: He's… he's trying.
STFC-RAL-Pickavance LT R22 G.02: the whole point of this run-through is so that he can see what camera angles he needs for what bits, so that we can make sure that people online
STFC-RAL-Pickavance LT R22 G.02: can see as well. Right. In which case, I want to get some screens, so we can set up a proper area.
STFC-RAL-Pickavance LT R22 G.02: It's not gonna be safe if we don't have our, full section.
STFC-RAL-Pickavance LT R22 G.02: So… When it comes to the area itself, hmm…
STFC-RAL-Pickavance LT R22 G.02: do we want to have a separate table altogether set up like here? Or could we just do it on the table like this? You could do it on the table like that, and then the whole point is to have the cameras on here as well, so you could do some things over here, and you can do some things
STFC-RAL-Pickavance LT R22 G.02: over here.
STFC-RAL-Pickavance LT R22 G.02: So, depending on where people are sitting, they're either watching it
STFC-RAL-Pickavance LT R22 G.02: Yes, yes. Here, or up there. Okay, cool.
STFC-RAL-Pickavance LT R22 G.02: And for technology, for the…
STFC-RAL-Pickavance LT R22 G.02: lecture itself. We want to have the mobile microphone, so we can, like, walk around… Yeah, you can have the lapel mics.
STFC-RAL-Pickavance LT R22 G.02: He has already provided, said Clipper. Eyes the blessing.
STFC-RAL-Pickavance LT R22 G.02: The oxygen.
STFC-RAL-Pickavance LT R22 G.02: I'm fine.
STFC-RAL-Pickavance LT R22 G.02: Oh, isn't.
STFC-RAL-Pickavance LT R22 G.02: Okay, I'm happy with that.
STFC-RAL-Pickavance LT R22 G.02: Cool, right. I need screens, so I might have to dive back to my lab to put those up. I mean.
STFC-RAL-Pickavance LT R22 G.02: don't necessarily… I mean, you could… because obviously there's no audience here at the moment, so you can just…
STFC-RAL-Pickavance LT R22 G.02: I assume they're perspecs, so you can see through them. Yeah, perspectives, you can see through them, but I can always,
STFC-RAL-Pickavance LT R22 G.02: say, oh, my book.
STFC-RAL-Pickavance LT R22 G.02: Having a perfect screen. How big are that? I feel you're going to struggle to see that. I was like, yeah.
STFC-RAL-Pickavance LT R22 G.02: Well, that's okay, because…
STFC-RAL-Pickavance LT R22 G.02: That's what the cameras are for, because that… because we're getting far away, because from the top camera angle can see… Yes. From that top angle.
STFC-RAL-Pickavance LT R22 G.02: Yaw.
STFC-RAL-Pickavance LT R22 G.02: Fines.
STFC-RAL-Pickavance LT R22 G.02: Might just do this.
STFC-RAL-Pickavance LT R22 G.02: Test.
STFC-RAL-Pickavance LT R22 G.02: Why are you not letting me select Zoom?
STFC-RAL-Pickavance LT R22 G.02: In progress.
STFC-RAL-Pickavance LT R22 G.02: No maintenance today.