Our modern answer to the Pyramids
Frank Wilczek, MIT, Nobel laureate (2004)
As a project, it's magnificent—i like to say it's our civilization's answer to the Pyramids of Egypt, but much better because it's driven by curiosity rather than superstition, and built on collaboration, not command. The scale isn't just vanity—everything has to be as big as it is. But it's not only big in physical size; it's extremely sophisticated, extremely delicate. It's probably the most complex thing we've ever done—we being humanity.
We have now a very well-established, highly tested, highly rewarded-with-Nobel-Prizes theory of the weak interaction that's based on a concept that's never been directly proved. The concept is that the universe is a kind of cosmic superconductor, not for electricity but for weak charges: what appears as empty space is anything but empty. Another way of saying that is we're living in a kind of ocean, surrounded by—something. But we've never isolated a water molecule; we don't know what the ocean consists of. The LHC [the Large Hadron Collider in Geneva] will discover what that is. That's the minimal achievement.
But I expect much more. We have a description of the world that's potentially magnificent and beautiful—in part—but has pieces missing. We have four fundamental forces—strong, weak, electromagnetic and gravity—and lovely ideas for how to tie them together. And when you try to follow that inspiration out, you find a lot of things work out very nicely, but it doesn't really work in detail, unless you expand the equation to include more stuff. Some of that stuff should be within the range of the LHC. So ideas about unification—that go by the name of supersymmetry—are really in play. We'll have a much more unified description of the world than we've had before, many more particles to play with [whose] properties will be a window into a vast new physics—a whole new world of fundamental behavior.
If you just take the particles we have and extrapolate their known behavior, you run into contradictions—you start to contradict basic principles of quantum mechanics or common sense. There has to be a deviation of some kind from the laws we have at present when you go up to high energy: if there's not a new particle, then we'll need different laws. That would be maybe even more profound than finding new particles—if we have to give up quantum mechanics or change what we mean by the laws. So finding new particles is much more conservative than the alternative. We'd have to unlearn a lot of what we know.
There will be less room for religion
Steven Weinberg, University of Texas, Nobel laureate (1979)
As science explains more and more, there is less and less need for religious explanations. Originally, in the history of human beings, everything was mysterious. Fire, rain, birth, death—all seemed to require the action of some kind of divine being. As time has passed, we have explained more and more in a purely naturalistic way. This doesn't contradict religion, but it does takes away one of the original motivations for religion.
If we put together something like a final theory in which all the forces and the particles are explained, and that theory also throws light on the origin of the big bang and gives us a consistent picture of cosmology, there will be a little less for religion to explain. But religion has evolved along with science. It is something created by human beings, and as human beings learn more and more, their religion changes. Today, especially in the more established religious sects in the West, they've learned to stop trying to explain nature religiously and leave that to science.
The more we learn about the universe, the fewer signs we see of an intelligent designer. Isaac Newton thought that an explanation of how the sun shone would have to be made in terms of the action of God. Now we know that the sun shines because of the heat produced by the conversion of hydrogen into helium in its core. People who expect to find evidence of divine action in nature, in the origin of the universe or in the laws that govern matter are probably going to be disappointed.
What will be completely satisfying will be to show that there was only one kind of nature that was logically possible and derive the laws of nature in the same way that we derived the principles of arithmetic. I don't think that will be possible, because we can already imagine logically consistent laws of nature that don't quite describe the world we see. We will always be somewhat disappointed. But people who believe in God have the same problem. They will never be able to understand why the God that they believe in is that way and not some other way. All human beings, whether religious or not, are caught in a tragic situation of never fully being able to understand the world we are in.
I don't believe in God, but I don't make a religion out of not believing in God. It is logically possible that something could be discovered that will make me change my mind, and it will be interesting to see if that happens. But I don't expect it. It is always possible that we will discover something in nature that cannot be explained in the naturalistic way that we've gotten used to in science and that will really require divine intervention. That hasn't happened. I don't know of any religious people who say that the breaking of the symmetry between the weak and the electromagnetic interactions requires divine intervention. Discovering the Higgs boson, or confirming the theory of electroweak symmetry breaking, is not going to upset people's religion.
Possible evidence of a 4th dimension
Brian Greene, Columbia University, string theorist
The one insight that we are most confident or hopeful about is supersymmetry. It's a little complex to describe in detail, but I can describe an implication: for every known particle species in the world—electrons, quarks and so on—we should see a partner particle that is as yet undiscovered. We find this possibility exciting because supersymmetry is an intrinsic quality of string theory. If you discover supersymmetry, it doesn't prove string theory right, but it does prove one of its central attributes to be right.
What Einstein did with general relativity, in terms of its role in theoretical physics, is give us an understanding of certain symmetries or qualities of space and time. Supersymmetry in essence is taking that to the next level. If supersymmetry is right, it's telling us that space and time have qualities that Einstein couldn't have dreamed of but naturally fit into the same progression that he started. There are other things beyond supersymmetry that again would tie into Einstein in a deep way that could also be found.
The LHC could provide evidence for more than three dimensions of space. One of the ways that we have formulated string theory in the last five or 10 years suggests that the following might happen at the LHC. What happens there is you slam one proton against another proton traveling in opposite directions near the speed of light. And there are literally trillions of protons going around the LHC at something like 11,000 times a second. And then you have these collisions. What might happen is there will be some debris created in the collision that gets ejected out of our three dimensions of space into a higher dimensional space, dimensions that we don't have direct access to. How would you notice that? If some debris gets rejected, it will carry some energy with it, which means that if you measure the energy just before the protons collide and you measure what's left over just after, you should have a little less at the end than you had at the beginning. That would be indirect evidence that energy had been lost to more dimensions.
[The follow up to the LHC is] already being planned: the International Linear Collider. You can think about the LHC as a very powerful microscope, but it's likely to reveal just the gross features of the new physics. The ILC is a machine of a different design that has the capacity to then take the gross road map that the LHC can provide and begin to really go down the little alleyways and enchanting avenues, to really explore the terrain with the kind of detail and precision that the LHC likely can't. Let's say some new particles are discovered at the LHC. The ILC would have the capacity to study the very fine detailed properties of those particles, to really produce them copiously and understand with great precision their mass, election charge, interactions, things of that sort, which the LHC may be able to roughly say. The ILC is one that really can get in there and describe the properties with fantastic precision.
No, it won ' t swallow up the Earth
Stephen Hawking , Cambridge University, mathematician
The large Hadron Collider will allow us to study particle collisions at energies three times greater than previous particle accelerators. We can guess at what this will reveal, but our experience has been that when we open up a new range of observations, we often find what we had not expected. That is when physics becomes really exciting, because we are learning something new about the universe.
The LHC is part of an international effort to unlock the secrets of the universe. It cost about $10 billion over four years, which sounds a lot, but which is only 0.005 percent of the world gross domestic product for that period. Can't we afford two hundredths of a percent to understand the universe?
And it is absolutely safe. There has been a scare story that it might create a tiny black hole that would swallow up the Earth. But if the collisions in the LHC produced a micro black hole, and this is unlikely, it would just evaporate away again, producing a characteristic pattern of particles. Collisions at these and greater energies occur millions of times a day in the Earth's atmosphere, and nothing terrible happens. The world will not come to an end when the LHC turns on. The LHC is feeble compared with what goes on in the universe. If a disaster was going to happen, it would have happened already.
Pointing to a future path for physics
Alan Guth, MIT, cosmologist
What we're trying to understand is the first fraction of a second of the history of the universe, and how the evolution that took place then put the universe on the path to become what it is today. Inflationary theory is a twist on the conventional big-bang picture. What changes is our understanding of the history of the universe for a very short period during the first minute. The theory modifies the evolution to include a brief period during which gravity is turned on its head and becomes repulsive instead of attractive. If inflation is right, this short period of repulsive gravity is the actual bang of the big bang, in the sense that it is what propelled the universe into its enormous expansion, which we're still seeing today.
I think many physicists, including me, feel that the direction of physics in the coming years is very uncertain. I'm talking about the actual science, not just the funding. The key shocker for many of us was the discovery about 10 years ago that the universe is accelerating. It was not expected theoretically, at least not by most of us, and it is very hard to understand in the context of the theories that we have been using all these years. The LHC is likely to play a major role in telling us the direction in which we should be moving.
Think of it like the Hubble telescope
Edward Witten, Institute for Advanced Study, string theorist
There's a chance that something would be discovered that wouldn't fit well with any of our ideas. The chance of finding higher dimensions—it's possible, but just barely possible. If everything is lined up exactly right, it's conceivable the LHC could do that. Energy would seem to disappear because the idea is that, when particles have a sufficiently high energy, they can escape into a higher dimensional world. If it's a long shot to get direct evidence for extra dimensions, it's even more of a long shot to get a clear black-hole signature at the LHC.
What the LHC really does is explore the energies at which the nature of the weak interactions can be understood. The important forces of nature are gravity, the nuclear force—also called the strong interactions—electromagnetism and weak interactions, which is probably the least familiar force to those who aren't physicists, responsible for certain forms of atomic radioactivity. The weak interactions are a big piece of the puzzle. They're the least understood because they're so weak. It's very mysterious.
We've already discovered the W and Z particles, which are two important ingredients in weak interactions. Putting together what we already know, we know the energy scale at which the weak-interaction symmetry is broken. And it's definitely in reach of the LHC. In fact, the LHC goes beyond that. That's the big question which I'm sure the LHC will answer.
You should think of the LHC as being something like the Hubble space telescope: it's built to explore the universe and understand it better.
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