TD Lee: Is the vacuum a physical medium?

0:00 If I may have your attention please, I welcome you to this afternoon's joint colloquium with the University of Pennsylvania. I'm William Edson, head of the physics department here at Drexel, and I'd like to ask Professor Sidney Bloodman of the University of Pennsylvania to do the formal introduction to our speaker. Since the early days of parody. In those days, not many people knew what parody was, and I remember that there was a cartoon in the New Yorker magazine that showed two southern senators discussing politics, and one of them was asking the other, what is parody? And I remember giving the cartoon to TV at that time. Well, as we all know, Dean Yang helped to tell us what parody was. G.B. began his education in China under wartime conditions when his university was literally by hand and foot to come to me. He was one of the first Chinese to come to this country after the war. He received his PhD in astrophysics and since then has worked in statistical mechanics, in hydrodynamics, particle physics, and astrophysics.

2:30 Today I would like to discuss with you, in fact I would like to take you a little bit way back really to the 19th century. At that time, in order to understand how the electromagnetic forces and later the electromagnetic waves can be propagated from one place to another, the vacuum In fact, I would like to show you some of the writings by Faraday in the small square. This was taken. Can you all see it? Can you see this in the back? Now then, I will try to read it. Faraday's Experimental Research, Note 3075. To the magnetic force external to the magnet, I am more inclined to the notion that in the transmission of the force, there is an action. Such an action may be a function of the ether. If there be an ether, it should have other uses than simply the conveyance of radiations. In this lecture, I would like to call your attention to the other uses.

5:00 However, since the non-relativistic Newtonian mechanics was the only available one at the time, the vacuum was thought to provide an absolute frame which can be distinguished from other moving frames by measuring the velocity of light. As you all know, this led to the downfall of the East and the rise of the North in about the turn of the century. This is my own cartoon. Here, there are two observers, one with velocity v. This coordinate is the prime system, this m prime, the x and t are related by the familiar Lorentz transformation, which indicates the propagation of the law. It's a constant. So the back freedom is Lorentz invariant. However, Lorentz invariant is not everything, and this of course is a physicist. The jogging should not be the only activity that a physicist can do. Therefore, we may ask, the Lorentz invariant vacuum, what kind of structure does it have? Is it complicated? How complicated? And that we must then pass on to the 1920s. The first theory that dealt with it was the Dirac's whole theory. And quantum electrodynamics, which we call QED, we know that the vacuum is complicated. How complicated? If that's provided how you look at it. If you take a very long time average, then this is the vacuum. However, if you take a short time average, if you look at it with the delta T, related to the uncertainty of delta E, then you will get a vacuum of where?

7:30 Plus will be the positron, net minus will be the electron, and the wavy line indicates the gamma rays. Now this complicated structure can be calculated because the fine structure comes in small numbers, and we can do that with great accuracy and give you the vacuum polarization to high order and then verify the experiment. In general, vacuum is the lowest energy state of a Lorentz invariant theory. But it can be complicated if any Lorentz invariant quantity, say a spin zero field at full momentum equals zero. So in other words, vacuum is Lorentz invariant, but Lorentz invariant quantity can still carry quantum numbers. So therefore, vacuum can have other... Now, the main questions or the main topics that we would like to study will be the following. What is the vacuum structure beyond quantum mechanics, because after all, as we have just mentioned, we can calculate to great efforts? That's the first question. The second question is, is the vacuum structure changeable? In other words, can we, by through physical experimentation, change this complicated structure at our disposal preferably? And the key that we would like to answer these questions will be the sentence that I just mentioned before, vacuum can be as complicated as any spin-zero field at full momentum, because you can be constant over a large moment. And the phenomena that we shall deal with will be two of the most remarkable phenomena in modern physics. The first is called missing symmetry, the second is called co-comprimacy, and we shall see from these two remarkable phenomena and with this key we will be able to answer some of these questions.

10:00 So what is missing symmetry? Symmetry principles have played an important role in physics since its very beginning. Gradually, symmetry principle has become the backbone. However, since especially the 50s, with very few exceptions, most of the symmetries used in physics have found to be broken, that they are not exact, that symmetry numbers are continuously missing, and this is called missing symmetry. That means the following. If I take the isosceles of all matter, if I take S, the spinness of all matter, or if I take the parity P of all matter, then I just clock it. Then I find... Every time when there is a natural decay, radioactivity decay, when a volcano produces a lambda particle, whenever in cosmic radiation there is an energetic collision, a strange particle can be created and decay, the decay of these things of all matter is not even. Now that is called missing symmetry. Aesthetically, this may appear disturbing. Why should nature abandon perfect symmetry? Physically, this seems also very mysterious. What happened to these missing quantum numbers? Where do they go to? Can it be that the matter of the world, they do not form a closed system? Can it be that if we introduce the vacuum, put matter and vacuum together, we can put the DDT of that equals zero? This, of course, is the underlying idea of the so-called spontaneous symmetry breaking, and the idea of which I will now try to explain.

12:30 Spontaneous symmetry breaking. It says that we can produce a phenomenological field which is Lorentz invariant, whose vector expectation value is not zero, and that field can carry quantum numbers. In other words, in short sentence, this means the following. We attribute the asymmetry that we observe to the state vector. Therefore, although the world that we live in is skewed, that we all know, but the laws of nature can remain symmetrical. You may ask, how do you know K-A-G is symmetrical? Because you can always put on the right-hand side of this is the minus-DDT of the vacuum. And whatever is missing in matter, you see it appears in the vacuum. A very good example to differentiate whether it's a company or it's physically real is, I'm sure that in Drexel or Pennsylvania you have the same system of retirement plans. Every month when you receive a check from the university, they deduct a certain portion. And they say it's for your retirement. You know, of course, you are not going to get the whole amount back. That will not happen. But, if it happens that you will never get anything, then you know there is something wrong. But you can get something back from the vacuum to matter, and that is the key. In order to differentiate whether the whole idea of the asymmetry is due to the state vector and not due to the Law of nature is that there must be circumstances you can reclaim some of the missing symmetry. Without that, it will be a totality. Now, how do we do this? Let us try to imagine, for example, we know the Earth as a magnetic field. Therefore, all terrestrial experiments will be subject to this magnetic field, will have a small amount of rotational asymmetry because Earth's magnetic field points distinguish the North Pole.

15:00 It is of course difficult for us to change the entire Earth's magnetic field, but we do not say the law of physics is rotationally asymmetric. We say there is a certain asymmetry of compass point to a direction is because the Earth is a big magnet. Even though we are not able to change the magnet by will, and the reason we are sure that the law of physics is rotation is symmetric, at least to the extent of the accuracy of the Earth's magnetic field, is because we are able to create in the local region a domain of magnetic field pointing to a different direction. By changing them, we can test. The law of physics regards to different magnetic fields and thereby asserts that it is indeed the law of nature that is symmetric and it is only the state vector, the world that we live in, that happens to be skewed. So we can then borrow the same idea. So that means, in order to claim something back, we must be able to create domain structures. Now how do we do that? Consider vacuum can behave like a scalar field since we are at the full momentum k mu equals zero. Now full momentum equals zero but the universe is finite since we know delta x times delta p one in the natural unit therefore the universe is finite meaning that your momentum can never be zero so really it's not full momentum equals zero it just means full momentum equals very small. So to begin with, the vacuum, the universe being finite, the vacuum is like a scalar field, a phenomenological scalar field, a very long wavelength. So we can imagine, if you need, if it is due to some scalar quantity that carries a corresponding number whose average is not zero, then perhaps we can change that value, not for the entire universe, but for a very large volume. So now you ask yourself, what does large volume mean for the local value?

17:30 Well, it seems to everybody, if it's as large as the galaxy, it should be pretty big. If I can change the expectation value over the entire Milky Way, then surely we can test the law of nature in that particular way. But after a while you will realize, So for our solar system, maybe it's pretty good for us. After all, you are dealing with decay of the lambda particle whose extension is 10 to the minus 13 centimeters. There you are. Once you get to the solar system, there's no reason for you not to accept the Earth as a reasonable large volume. United States, Jackson University, this room, and you come down to any land that's bigger than 10 to the minus 13 centimeters, 10 to the minus 12 centimeters. In which case, then we can do experiments. So, we now consider a volume which is big compared to the microscopic particles, say like the extension of a granule mu, 12 cm or so. Now, by some, which we shall discuss, if we can change the scalar quantity which over that volume, which carries the symmetry number, change its expectation value not to the UU phi value but to a different value, then we can test. Well, it is indeed true that the laws of nature are all symmetrical with respect to whatever the symmetry that we are dealing with. How can we do that? We just draw the analog of the magnetic field we have talked about. What we do, imagine this is the magnetic field. When you want to create a domain, change the magnetic field in the local region, So the rock and rotate the spin in a different direction. Likewise, if it's a scalar quantity, we take anything that interacts with the scalar quantity. We can call it the metal source. So we take a J as a metal source, apply over a large volume, and the volume can be, say, like a heavy iron. And then we can simply rotate this, change its value to a different value of phi expectation, and this I shall call vacuum expectation. And by doing this, which will be a relativistic, heavy ion experiment, we perhaps can explore the region of vacuum excitation.

20:00 Experiments of such are still under investigation, and a few years ago Giancarlo Wick and myself had speculated that this may lead to, for example, the abnormal nuclear matter. In order to change the vacuum even over a volume large compared to the microscopic distance but say 10 to the power of 12 centimeters, it would not be easy. In order to reclaim all the missing symmetry, it would not be easy. And we can ask, since in our universe we know there are a lot of metal sources, can't be that these vacuum excitations, they have already been existing. All we need is to look around. The next topic is the quark component. And for that, we must be prepared to accept the quark model. And I will give you the argument. First, what is the quark model? Why, ridiculous it may seem, most physicists do believe in them. And how can we understand it? And then in the vacuum. So let's now take a brief excursion to the quark model. Introduced by Zweig and Gell-Mann, it is to say that all hadrons are composed of quarks, which I call Q, and antiquarks, which I call Q-bar. Methons, such as pine, low-methons, are made of Q-bar compounds, like a simple diatomic molecule. Variants, which would be proton, neutron, remnant, and so on, are three-core compounds. The cores are called down, strength, charm, bottom. The names are not mine, so I do not want to apologize too much.

22:30 There are masses of up and down near zero, strength about 100 MeV, charm about 2 GeV, bottom about 5 GeV. If I call electron the charge is one, or rather the proton the charge is one, then up is two-thirds, down is minus one-third, strange is minus one-third, charm is two-thirds, bottom is minus one-third. Now, some of the rationales you can understand quite easily. The typical barrier will be proton, whose charge is one. You need three quarks to make up a barrier, therefore the charge of the quark should be fractionate in one-third as a unit. Now, variance, the spins, they are all of one-half spin. You take three quarks to make one-half spin, therefore the quark spin must also be half integer. Therefore, technically we say they are Fermi principles. That means whatever the state you are in, you can only put one. Now, you want to put three quarks in one variance state. It's difficult, and this was invented by Greenberg. The easiest way to say there are three different kinds of quarks called colors. If you like blue, white, red, and say blue, white, here I will call it color equals one, two, three. If you have three different colors, the product made of three quarks, they are all in the same state, three there, without violating the Fermi principle. Now you say, well, that's good. It makes it possible to put three forks in one state. But you are indeed into trouble, because looking back into the method, the methods are made of cork and cork. So you have a red cork, anti-red, good, one kind, blue cork, anti-blue, another kind, red cork, anti-blue. But if the cork has three kinds, the anti-cork will be also three kinds. There are nine kinds of pine. That's eight too many. Even worse for the barrier, you can now put three in one step, fine, your book has three different colors, there are three quarters, so three to the cube will be 27 different kinds of protons, that's 26 to me. So we say, wow, can we resolve also quite elegantly? But I say that all observed hadrons are colorless, because only singlet, namely, you must take mesons are always red anti-red plus blue, color is singlet, and that's what it is, never anything else.

25:00 And how about the various, you can do the, since the lighting is a little bit, you can, if you can see my fingers, you consider your three axes. This is red, blue, white. You make your volume, you, well, now I can draw it. This is the quark colored red, quark colored. Now, under the rotation of the axes, the volume is in red, and that is, so that is just the three quarks, epsilon, abc, and this asymmetrical tensor that makes up the. Okay, then they say that's great. And furthermore, we know the masses. Now we can explain the spectroscopy. That's all verified. The only person that it has not been seen, or at least has not been seen, outside Stanford University. So you wonder why? Well, you say, well, maybe the whole thing is a bit wacky. But we have more direct evidence. Though it has not been seen outside Stanford University, it has been inferred in the nearby place, namely Slab, and also the distant place, namely Daisy. Now that is from direct experimental evidence. Now we must catch this. It's a little bit weird. It's weird by first postulating everything is made of pores. Then you discover quarks are fractionally charged, they have spin, and they are fermions, they have color, but we never see color, and the masses are small, so we don't ever produce them, so there's something very strange. Let's look at the direct experiment. So the first round of evidence are from spectroscopy.

27:30 Not convincing, but now we will bring something a little bit more convincing. Let's consider electron-positron colliding. Let's consider a photon emitting mu minus and mu plus, and likewise emitting quark and antiquark. Let's call the muon charge 1 in the same unit quark charge capital Q sub. Let's consider the center mass energy to be much bigger than 2 times the mass of the quark. So this reaction goes. And, that's also important, and let us neglect The strong interaction between quarks and ending quarks. You say, that can't be true because they make up all the hadrons, they have a strong interactive body. But since we are going to errata on the beams, let's be bold and assume that. If you assume that, then the ratio of the cross-sections can be gotten very easily because the amplitude of the creation provides the charge, the cross-section provides the charge squared. If there are three colors, you should multiply it by three. So this is a very simple formula. There's every reason why it should not be true. First, quark may not be there. Second, the mass may be very big. That's why you don't see. And third, there's no color. And fourth, they have strong interactions, so you cannot compare. So there are more than one reason why it should not be right. But the converse, if it's right, that says there are all these same things, maybe. So that's the logic. So let us now consider this ratio under these assumptions for certain energy, then we count all the quarks within this, certify this criteria, energy is bigger, bigger than the two times mass of quark, and so it's three times the charge of the quark for those quarks which can be produced up to that energy. So we plot now the energy in the center mass system in JAB and the ratio to the mu pit.