Gerard ′t Hooft

 Name: ′t Hooft, Gerard

 Postal address: Spinoza Instituut,

 Leuvenlaan 4

 Postbus 80.195

 3508 TD
 Utrecht.

 Voorts verbonden aan:

 Institute for Theoretical
 Physics

 Universiteit Utrecht

 Leuvenlaan 4, 3584
 CC Utrecht

 Tel.: +31 30 253 5928

 Tel.  +31 30 253 1863

 Fax:  +31 30 253 5937

  e-mail: g.thooft@uu.nl

Warning: due to severe clogging of
this email post box, I can no longer guarantee that received messages will be
processed and/or answered.

 secretary: Els Brochard, E.Brochard@uu.nl

Discussing Magnetic Monopoles with Rembert Duine

Professor Theoretical Physics

Click here for lectures (notes, PowerPoint files)

Research interests:

Gauge theories in elementary particle physics.
This was the topic of the 1999 Nobel Prize. An idea was proposed by C.N. Yang and Robert Mills in 1954: they suggested that particles in the sub-atomic world might interact via fields that are similar to, but more general than electricity and magnetism. But, even though the interactions that had been registered in experiments showed some vague resemblance to the Yang-Mills equations, the details seemed to be all wrong. Attempts to perform accurate calculations were frustrated by infinite - hence meaningless - results. Together with my advisor then, and my co-Nobel-laureate now, M. Veltman, I found in 1970 how to renormalize the theory, and, more importantly, we identified the theories for which this works, and what conditions they must fulfil. One must, for instance, have a so-called Higgs-particle. These theories are now called gauge theories.

It was subsequently discovered that, indeed, the observed details of all known forces exactly agree with this picture. First it was found that the so-called weak force, in combination with the more familiar electro-magnetic one, is exactly described by a Yang-Mills theory. In 1973 it was concluded that also the strong force is a Yang-Mills theory. I was among the small number of people who were already convinced of this from early 1971. During the later 1970s, all pieces fell into place. Of all simple models describing the fundamental particles, one was standing out, the so-called `Standard Model'.
Gauge theories are the backbone of this Standard Model. But now it also became clear that this is much more than just a model: it is the Standard Theory. Great precision can be reached, though the practical difficulties in some sectors are still substantial, and it would be great if one could devise more powerful calculation techniques. Also, in spite of all its successes, the Standard Model, as it is formulated at present, shows deficiencies. It cannot be exactly right. Significant refinements are expected when the results of new experiments become known, hopefully during 2010 and subsequent years, when the European particle accelerator LHC becomes fully operational.

Quantum gravity and black holes .
The predominant force controlling large scale events in the Universe is the gravitational one. The physical and the mathematical nature of this force were put in an entirely new perspective by Albert Einstein. He noted that gravitation is rooted in geometric properties of space and time themselves. The equations he wrote down for this force show a remarkable resemblance with the gauge forces that control the sub-nuclear world as described in the previous paragraph, but there is one essential difference: if we investigate how individual sub-atomic particles would affect one another gravitationally, we find that the infinities are much worse, and renormalization fails here. Under normal circumstances, the gravitational force between sub-atomic particles is so weak that these difficulties are insignificant, but at extremely tiny distance scales, of the order of 10^-33cm, this force will become strong. We are tempted to believe that, at these tiny distance scales, the fabric of space and time is affected by quantum mechanical phenomena, but exactly how this happens is still very mysterious. One approach to this problem is to ask: under which circumstance is the gravitational force as strong as it ever can be? The answer to this is clear: at the horizon of a black hole. If we could understand the peculiar physical phenomena that one expects at the horizon of a black hole, and if we could find a meaningful description of its quantum mechanical laws, then perhaps this would open up new perspectives.

Fundamental aspects of quantum physics. I have deviating views on the physical interpretation of quantum theory, and its implications for Big Bang theories of the Universe. This topic has been expanded upon in recent publications, cf. "The mathematical basis for deterministic quantum mechanics"; The Free-Will Postulate in Quantum Mechanics; Entangled quantum states in a local deterministic theory, arXiv:0908.3408 (see my publication list).

To me, Nature is a big jig-saw puzzle, and I see it as my task to try to fit pieces of it together. Click and cut the pieces you see here from the screen and see how they fit, or: read more about it in my book: `Bouwstenen van de Schepping' (Prometheus/Bert Bakker, ISBN 90 351 1327 6) or its English version: `In Search of the Ultimate Building Blocks', Cambridge Univ. Press, Paperback 9.95 pounds, 14.95 US dollars, ISBN 0 521 578833; hardback 27.95 pounds, 39.95 US dollars, ISBN 0 521 550831) . In `Planetenbiljart', a personal view is described of the potentials of scientific and technological developments in the future. Which possibilities are there and are there things that will be impossible forever? Maybe you enjoy SF novels as much as I do, but don't mistake them for predictions of the future.

Important message for autograph collectors: Some people are afflicted with the desire to collect photographs and autographs of Nobel Prize winners. I am very flattered when I receive such requests, but I think I have done my share. I am sold out now. No more photographs or autographs, with apologies.

Opzienbarende Utrechtse ontdekking revolutionair voor woon-werkverkeer. Lees verder.

More and more frequently, I receive letters and mails from wise people outside physics, telling me that "they know" that the Higgs will not be found, that our theories are baloney, how dare we spend billions of public funds to build machines such as LHC, "to prove, against better judgment, that our theories still stand a chance of being correct", and so on.

Well, lads, I am not going to answer all of you in person. What you have in common is a blissful ignorance of the scientific facts concerning the Standard Model. Fact is that the W+, W- and the Z boson each carry three spin degrees of freedom, whereas the Yang-Mills field quanta, which describe their interactions correctly in great detail, each carry only two. Those remaining modes come from the Higgs field. What this means is that three quarters of the field of the Higgs have already been found. The fourth is still missing, and if you calculate its properties, it is also clear why it is missing: it is hiding in the form of a particle that is difficult to detect. LHC will have to work for several years before it stands a chance to see the statistical signals of this Higgs particle. What compounds the matter even more is that there may well be several sets of Higgs fields. If there are two, which is eight quarters of the field, we will get five Higgses rather than one. This would be a quite realistic possibility but it would make the detection of each one of them even harder, because they cause more complex statistical signals that are more difficult to predict.

Theories without any Higgs particle are possible but ugly and have been practically ruled out by observations. In such theories, composite bound states of other particles have to play the role of a Higgs, which requires the existence of very strong new interactions, of which there is presently no evidence at all, and it would make the perfect agreement found today between observations and the Standard Model highly improbable.

If no Higgs is found at all, and all present ideas would be ruled out by LHC - which is unlikely - this would in no way make LHC useless. Quite to the contrary, this would lead to lots of work for theoreticians to do, and, more importantly, this would imply the existence of new strong forces with a plethora of highly interesting particles just round the corner, waiting to be discovered by LHC or its successors. There's no way that this field of research can become dull.