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Is the Universe a Giant Hologram?

February 11, 2009 on 3:21 pm | In Quantum, String Theory, cosmology | 32 Comments

Some days the questions I get are easy, and some days I get questions from our longtime reader, Ben. This past week, there have been reports all over the news that our world may be a giant hologram. Let’s take a look at what’s going on.

In Hanover, Germany, there’s an experiment called GEO600. These are two perpendicular lasers, and they shoot out for thousands of feet, get reflected, and come back to their original location to make an interference pattern.

Now the reason this is important is because gravitational waves cause ripples in space in a certain way. These perpendicular lasers are particularly sensitive to what gravitational waves do, and the interference pattern will shift in a very particular way if gravitational waves pass through them. This is the same idea that’s behind the upcoming LISA mission.

Now, GEO600, like every laser interferometer we’ve ever built, has not seen any evidence for gravitational waves. But it has seen something that it can’t explain, and that’s always interesting for an experiment.

It found some extra noise, above and beyond what can be predicted/explained by things like the vibrations of the Earth, temperature fluctuations, or instrumental noise. What does this look like? Whenever you do your experiment, you do your best to understand what noise you expect to see, and then you look for deviations from this. GEO600 saw something like this:

So there are two possibilities now: either there’s a source of noise they haven’t figured out, or something physically interesting and novel is causing this. Now, historically, whenever experiments are done, it’s almost always unexpected noise that causes something like this to happen. But once in awhile, there really is a new effect that we have going on.

It’s very important to state, clearly and unambiguously, before we go any further, that this may simply turn out to be noise. This may not be a physical effect at all, and that no other similar experiments (such as LIGO) see these effects.

But if it is a physical effect, Craig Hogan of Fermilab has come up with an extremely interesting possible explanation. He says that this excess noise could be a sign that our Universe has an extra dimension to it. How does this work? Let’s think of a hologram:

A hologram has all the information you could ever want about the dimensions of a 3-D object, but it has it all in two dimensions. For instance, you could tell some object’s (or someone’s) length, width, and depth just from looking at a 2-D hologram. All of the information is encoded in there.

Well, our Universe may be the same exact way. We know about our 3 space dimensions and our 1 time dimension. But we may have more dimensions of space than we know about; many interesting theories have them. One possible consequence is that these extra dimensions could cause extra “blurring” of our 3 regular space dimensions at very small lengths.

Now, this is very interesting, because the noise we see in the GEO600 experiment causes the laser light to blur on scales of about 10-16 meters and below. This is smaller than the size of a single proton, but amazingly, our technology is sensitive enough that we can detect it! But is this blurring due to extra dimensions? Let’s see what the people connected with the experiment say about Craig Hogan’s idea:

However Danzmann is cautious about Hogan’s proposal and believes more theoretical work needs to be done. “It’s intriguing,” he says. “But it’s not really a theory yet, more just an idea.” Like many others, Danzmann agrees it is too early to make any definitive claims. “Let’s wait and see,” he says. “We think it’s at least a year too early to get excited.”

The longer the puzzle remains, however, the stronger the motivation becomes to build a dedicated instrument to probe holographic noise. John Cramer of the University of Washington in Seattle agrees. It was a “lucky accident” that Hogan’s predictions could be connected to the GEO600 experiment, he says. “It seems clear that much better experimental investigations could be mounted if they were focused specifically on the measurement and characterisation of holographic noise and related phenomena.”

So it looks like this is worth further investigation, but it’s way too early to draw any definitive conclusions. But it’s a possibility, and for something as grand as this, for something that would forever change the way we view our Universe, I think it’s worth investigating further, and so does the entire GEO600 team.

What do you think?

Quantum Mechanics: Einstein vs. Bohr

December 22, 2008 on 2:42 pm | In Physics, Quantum | 168 Comments

Einstein called the cosmological constant his “greatest blunder.” Einstein was wrong. The cosmological constant was a neat idea for General Relativity that’s still important today, and General Relativity was, IMO, his greatest accomplishment. The idea that space and time are curved by matter and energy, and that curvature is what makes gravitational force is profound and beautiful, and profoundly affects the way I look at everything that involves Gravity.

But Einstein had his blunders, oh yes. The big thing Einstein was wrong about? Quantum mechanics. One of Einstein’s more memorable quotes was this:

“God does not play dice with the Universe.”

What was this in reference to? In good ol’ regular, classical physics (including General Relativity), if you know all the initial conditions of your system and you know the laws of physics, you can figure out exactly what’s going to happen. In quantum mechanics, though, if you know the initial conditions and you know the laws of physics, you can figure out the probability of various outcomes happening, but you can never know which one will definitely occur until after it’s over. Einstein didn’t believe it, and held a series of great debates with Neils Bohr over the issue.

But this isn’t Lincoln-Douglas. This is physics. You want to settle something? You do it with an experiment. So Einstein (and his grad student, Nathan Rosen) tried to show that the Universe had to be deterministic. Their hope was that there are variables that we just haven’t seen yet that determine what’s going to happen. It doesn’t, and there’s now a theorem that tells us why. So Bohr was right, and Einstein was wrong. The Universe isn’t deterministic, not even according to the laws of physics.

But this is abstract. Let’s give you a concrete example of an experiment that you can do (well, in principle) to help you better understand this. Imagine I’ve got a big screen with two narrow slits that are very close together. And I’ve got a Cathode Ray Tube that shoots out electrons. If I leave both slits open and shoot a whole myriad of electrons, the electrons go through and act like waves.

They interfere with one another, and produce a nice pattern where they have constructive interference (where lots of electrons land) and destructive interference (where no electrons land). You can keep track of where the electrons land over time, and here’s what you see when you add it all up.

Cover either slit up, and the interference pattern goes away. So it needs two slits. What about electrons? What if you fire them one-at-a-time? Sure, electrons can interfere with other electrons. But, can one electron interfere with itself? What do we see if we shoot the electrons through the double slit experiment one at a time? Well, it takes a long time to get enough electrons to see, but here’s what the results are:

Amazing. The electron must be interfering with itself! How does it know where to go? And how do you determine which slit it went through?

Now, here’s where things get interesting. You can set up some light sensors on each of the slits to figure out which one the electrons go through. When the electron passes through the slit, if a photon (a particle of light) hits the electron, you know which slit it goes through. If a photon doesn’t hit it, you don’t know.

Here’s the crazy part: if you hit the electron with a photon, the interference pattern goes away. You force it to go through only one slit, and you just get two bumps on your screen, one for each of the two slits. If you don’t hit the electron, though, the electron does interfere with itself, and you get the interference pattern above.

If you look, and you try to know, you will destroy the quantum mechanical effects. If you don’t look, though, God plays dice while your back is turned.

It’s messed up. And it’s awesome. Was Einstein wrong? About quantum mechanics, yes. Yes he was. And that, my friends, is what Einstein’s greatest blunder really was. Einstein never accepted quantum mechanics, never accepted that this is the way the Universe works. If you can accept and understand this, then at least about this one thing, you’ll have taken a step that Einstein never did.

The Nobel Prize in Physics

October 8, 2008 on 2:07 pm | In Physics, Quantum | 3 Comments

As the dollar continues to tank worldwide, those 10,000,000 Swedish Kroner are looking better and better. Not to mention that spiffy medal that comes with it:

In a surprise to no one, 2008 was not my year. This year, the Nobel Prize in Physics goes half to Yochiro Nambu for spontaneous symmetry breaking and the other half (jointly) to Makoto Kobayashi and Toshihide Maskawa for discovering the symmetry which predicts (at least) three generations of quarks.

Let’s start with Nambu and spontaneous symmetry breaking. First off, I saw Nambu speak when I was a grad student in 2003. I’ve got to say, although he’s an extremely impressive theoretical physicist, he is an atrocious communicator. You might have been able to guess this from the fact that the particles that come out of spontaneously broken symmetries are called Goldstone bosons after Jeffrey Goldstone, who explained Nambu’s results, rather than Nambu bosons. Still, good for him for winning the Nobel Prize; this was his discovery after all. The way this works is that you can imagine being at the top of a sombrero, all happy where you are, until something forces you to roll down in one particular direction.

Do you roll toward the left? Right? Front? Some other direction? Well, in physics, this makes a difference. Perhaps rolling towards the left means we make more matter than anti-matter, and our Universe just happened to make the symmetry break in that direction. There are plenty of other examples for what symmetry breaking does, including causing the weak force to be so much weaker than the electromagnetic force.

The other half goes to Kobayashi and Maskawa, who not only discovered that there should be at least 3 generations of quarks, but who determined how they mix with one another. That’s right; when you make subatomic particles, you don’t make one that’s just 3 quarks or a quark-antiquark pair. Instead, more often than not, there are mixtures of different types of quarks or quark-antiquark pairs inside of there. This explains lots of weird things, including CP violation.

There are a couple of people who got the shaft if the award went to these three, including the aforementioned Jeffrey Goldstone, who pointed out that you get massless particles whenever you break a symmetry, and Nicola Cabibbo, who was instrumental in the discovery and explanation of quark mixing. (They don’t call it the CKM mixing matrix or the Cabibbo angle for nothing!)

It’s probably irrelevant, since I’m particularly happy that the Nobel Prize went to physicists who are closely connected to explaining why the Universe exists the way that it does. Why is there more matter than antimatter? Why do particles have the mass that they do? Why is the weak force so damned weak? Broken symmetries explain these, and without the three Nobel Prize winners this year, we would be a lot further from the answers than we are now. Kudos to the winners!

How “Quantum” is the Big Bang?

May 13, 2008 on 11:36 am | In Quantum, Scientific papers, big bang | 12 Comments

There is a very techincal paper this morning by Martin Bojowald that asks the question, How Quantum Is The Big Bang? Let me break it down for you.

If you took a look at empty space and zoomed in on it, looking at spaces so small that they made a proton look like a basketball, you’d find that space wasn’t so empty after all, but was filled with stuff like this:

What are these? They’re little pairs of matter particles and anti-matter particles. They spontaneously get created, live for a brief fraction of a second, and then run into each other and disappear. That’s what happens on very small scales, in the quantum world. (This is known as the Heisenberg Uncertainty Principle, and it actually happens!)

Well, the Universe today is huge. But it wasn’t always; back when the Big Bang was happening, all the matter and energy in the Universe was concentrated into a volume so small that these quantum effects were important!

So now, we can ask the question: how important were these quantum effects at the time of the Big Bang? (FYI: this is talking about what happens at a singularity, so this is even before inflation!) And what he basically found is that at these super-high densities, you start to run into something very interesting. Remember the Pauli Exclusion Principle? It says that no two fermions (e.g., protons, neutrons, or electrons) can occupy the same quantum state. You put all the matter in the Universe into a small enough volume, and you wind up “squeezing” everything together!

And what he found, as best as I understand it, is that the quantum state of whatever’s in the Universe determines what type of Big Bang you get! Is it the same in all directions? Well, that depends on what the quantum state of the Universe is. Will it start expanding, contracting, or oscillating? Again, depends on the quantum state. We don’t know what that state is, especially in the context of inflation (which might wipe out all of that information), but this is what they’re trying to figure out! No definitive answers yet, but at least the quantum gravity people have gotten to the point where they can start to ask this question!

Will Physicists Find God?

March 27, 2008 on 2:05 am | In Quantum | 29 Comments

WARNING: Sensationalism ahead! Are you kidding me, Newsweek? They really titled their article Will Physicists Find God? Presumably, the title is named because physicists are searching for the Higgs Particle, and the title is taken after Leon Lederman’s (mediocre, IMO) book, The God Particle. Leon’s a pretty humorous guy, and was told by his Editor (according to him, anyway) that he couldn’t name his book, “The Goddamned Particle,” which is what he called the Higgs, so he shortened it.

For better or worse, the article is an interview with Steven Weinberg (left), one of the most illustrous living physicists. Steven is a Nobel Laureate and a huge figure in both the communities of theoretical particle physics and theoretical cosmology, having made tremendous contributions and written very important books and textbooks on both topics. (His book The First Three Minutes is still one of the best popular science books I’ve ever read.) He also went to the same High School as I did, albeit 46 years earlier.

The interview, however, is more annoying than anything else. Why? Because Steven Weinberg is very prominent, philosophically, as an Atheist. And like many scientists who are atheists (and I find this unfortunate), he has copious amounts of vitriol for religion in general. And the interviewer lures him into talking about that from the get-go. And he bites. Here’s an excerpt:

After this experiment, will we have a final theory of how the universe was created?

It is possible that this experiment will give theoretical physicists a brilliant new idea that will explain all the particles and all the forces that we know and bring everything together in a beautiful mathematically consistent theory. But it is very unlikely that a final theory will come just from this experiment. If had to bet, I would bet it won’t be that easy.

As we come closer to developing an ultimate theory of the universe, how will this impact religion?

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.

This is reasonable so far, but she really goes after his religious positions, asking the following questions at various points:

  • What about possible contributions toward finding a final theory? Would that upset religious believers?
  • But won’t some people expect to find the presence of a grand designer in that final theory?
  • Are they also going to be disappointed about our position in nature, our purpose?
  • Do you think most people have that kind of courage?
  • At some point will it be possible to find proof that God or the Ultimate Designer does not exist?
  • Would it be accurate to say that you are an atheist?
  • Could something found in the Large Hadron Collider or in future experiments make you change your mind?

The problem I have with this type of interviewing is that it really assumes the following tension: you can have science, or you can have faith, but if you accept what the natural world is telling us about itself, you have to reject everything about the divine world. Now Weinberg doesn’t make this statement (but there are plenty of science bloggers out there who do, and I find them way out of line), but that’s really what this article is about. It started with Galileo, it continued (and still continues) with Darwin, and seems to have gotten worse.

As a cosmologist, I have no qualms stating that the laws of science do an excellent job of explaining how life as we know it on Earth evolved to be the way it is, beginning with the Big Bang and following the (sometimes simple, sometimes not) laws of Physics, Chemistry, and Biology. But does that mean that there are some things, in principle, that are unknowable about the Universe? What if I told you that there are some questions science can’t answer, because, for instance, there isn’t enough energy in the Universe to figure them out? I don’t have the answer as to where the Universe came from, where the laws of nature that govern it came from, and I don’t know that science could ever provide those answers. But we answer what we can, and if we’re responsible scientists, we don’t draw conclusions about the things we have insufficient information about. I wish that were easier for people to understand.

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