Starts With A Bang! » Quantum http://startswithabang.com Ethan Siegel's blog/video blog about Cosmology, the Universe, and everything else Sat, 04 Apr 2009 20:12:38 +0000 http://wordpress.org/?v=2.3.2 en Is the Universe a Giant Hologram? http://startswithabang.com/?p=1486 http://startswithabang.com/?p=1486#comments Wed, 11 Feb 2009 22:21:39 +0000 ethan http://startswithabang.com/?p=1486 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?

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Quantum Mechanics: Einstein vs. Bohr http://startswithabang.com/?p=1304 http://startswithabang.com/?p=1304#comments Mon, 22 Dec 2008 21:42:41 +0000 ethan http://startswithabang.com/?p=1304 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.

]]> http://startswithabang.com/?feed=rss2&p=1304 The Nobel Prize in Physics http://startswithabang.com/?p=982 http://startswithabang.com/?p=982#comments Wed, 08 Oct 2008 21:07:52 +0000 ethan http://startswithabang.com/?p=982 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!

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How “Quantum” is the Big Bang? http://startswithabang.com/?p=1822 http://startswithabang.com/?p=1822#comments Tue, 13 May 2008 18:36:53 +0000 ethan http://startswithabang.com/?p=1822 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!

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Will Physicists Find God? http://startswithabang.com/?p=1775 http://startswithabang.com/?p=1775#comments Thu, 27 Mar 2008 09:05:07 +0000 ethan http://startswithabang.com/?p=1775 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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Q & A: Where does Matter Come From? http://startswithabang.com/?p=1750 http://startswithabang.com/?p=1750#comments Tue, 04 Mar 2008 19:56:29 +0000 ethan http://startswithabang.com/?p=1750 I love The Straight Dope. For 35 years, people have written in and asked some of the most difficult-to-answer questions on any topic you can think of; the staffers, writing under the pseudonym Cecil Adams, do their best to get to the bottom of their questions. Well, they also have a message board, and I saw one of the most difficult questions I’ve ever seen there:

Where does all the matter in the universe come from?

I’m no[t an] astrophysicist but I understand a little about the Big Bang Theory and also that there’s lots of stuff we don’t know or probably ever will know about it.

But the universe is awfully big and must have an awful lot of matter in the form of asteroids, stars, asteroids and suchlike. Did all matter in the universe originally exist at the centre of the Big Bang or is new matter being constantly created? If so, how?

None of the responses up there even begin to do this question justice, so let’s take a look ourselves. First off, there are two possible interpretations of this question, and I need to choose which one to answer. Is the question asking:

  1. Why is the Universe full of stuff? That is, why is there anything with any energy at all instead of nothing? Or…
  2. Why is the Universe full of matter? Energy could take any shape or form, but why matter, and how did it get there?

I’m assuming the second one (although if someone wants to ask the first, I’ll give it a shot); Why is the Universe full of normal matter? This isn’t something we expect, mind you. Here’s what we know as normal matter:

protons, neutrons, and electrons make up all the planets, stars, gas, and dust that we know and observe in the Universe. But the problem is, whenever we go into a laboratory and try to make some of this normal matter, for every particle of normal matter we make, we also make one of antimatter. But the Universe as we know it is made up almost exclusively of matter, with almost no antimatter. Every galaxy we see is matter, not antimatter. Every cloud of gas and dust we see is matter, not antimatter.

Why? If we take a look at wikipedia’s Unsolved Problems in Physics article, this is the second one on the list. But there is a whole bunch we do know about it, even if we don’t know the entire story.

First off, and this is the first rule of any scientific inquiry, is no cop-outs. That means, we would never just say, “Oh, it had to be there from the start of the big bang.” No; we want to figure it out, so we want to start with equal amounts of matter and anti-matter, and see if we can make more of one type than the other, naturally. We call this process Baryogenesis (other articles here and here).

So what do we need to make it happen? We need three things, known as the Sakharov conditions:

  1. You need an interaction that violates Baryon number conservation, which means you need to be able to make more protons than antiprotons or something akin to that.
  2. You need to violate CP-symmetry, which means (in English) that you need particles and antiparticles to decay into their various products at different rates.
  3. You need to be out of thermal equilibrium.

So, how can we do that? Let’s give you my favorite example; let’s assume that at some high enough energy, there are superheavy particles called X. The X has a charge +4/3, and there’s also the anti-X, with charge -4/3. When the Universe is very hot, it can be stable, and you make equal numbers of X and anti-X particles. Now, these X and anti-X particles aren’t stable, and they decay. Maybe the X-particles decay like this:

And make a positron and an anti-down quark (1/3 of an anti-baryon). Or maybe they decay into two up quarks instead (2/3 of a baryon). But let’s say the anti-X-particles also decay (because decays happen when the Universe cools and becomes unstable — that’s condition 3): they can decay into electrons and a down quark (1/3 of a baryon), or two anti-up quarks (2/3 of an anti-baryon). But what if the X decays into 49% positrons and anti-downs and into 51% two ups, and the anti-X decays into 51% electrons and downs and 49% two anti-ups? Well, that’s what can happen if you violate CP-symmetry (that’s condition two). Let’s put it all together and see, at the end of the day, what are you left with? A bunch of particles and antiparticles that will find each other and annihilate (down/antidown, up/antiup, and electron/positron), but then you’ll have that 2% left over! And what is that 2% made up of? Electrons, down quarks, and up quarks — just the stuff you need to make normal matter! And so you meet all three of these conditions, and just like that, you can make more matter than antimatter, starting with equal amounts of both!

Now, we aren’t sure that this is how it happens, nor are we sure that any of these related methods is how it happens either. But we can pretty definitively say that the Universe is made up of matter and not antimatter, and that there are a number of physical ways to make more matter than antimatter in the Universe. It isn’t being created now, nor is it fair to just assume it was created at the Big Bang, but it looks like we can make it rather shortly after the Big Bang, and pretty much all in one go. And that tiny little asymmetry, the little extra bit of matter that was created as opposed to antimatter, makes up and gives rise to everything (except the Microwave Background) that we see today. Pretty neat!

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Faster-Than-Light II: Information? http://startswithabang.com/?p=1725 http://startswithabang.com/?p=1725#comments Fri, 08 Feb 2008 23:12:35 +0000 ethan http://startswithabang.com/?p=1725 To follow up on the faster than light post here, let’s ask another question:

If you can make a way of transferring information that doesn’t involve matter, is that information limited by the speed of light?

First off, let’s go over what information is, and then we’ll talk about how transferring information without matter is even possible. Information is anything that’s organized in a meaningful manner. Take a look at the following three sentences:

  1. This sentence contains some information.
  2. Tihs scnnteee cainntos smoe imnfriatoon.
  3. Not a imfro nimsoe mnoisn ctrnsnet sihto.

Each of the three sentences contains the same number of bits, the same exact letters, but they are arranged differently. The first sentence is arranged in a meaningful manner, and is easily readable. The second sentence is still legible by many due to a trick of human perception, but the arrangement of letters is far from optimal to convey the intended information. The third sentence, which contains the same letters in a completely random order, contains no meaningful information.

Why is the first sentence meaningful, but the third one isn’t? It’s because we know how to decode the letters in the first sentence, and turn it into useful information, as opposed to the third one. That’s how Morse code (left) worked with a telegraph; a simple set of dot and dashes could be used to reconstruct an entire language.

Computers work off of a very similar (binary) language, using 0s and 1s instead of dots and dashes to encode their language. DNA has a similar alphabet, based on a 2-bit language (ACGT) instead of a 1-bit language. The alphabet used isn’t important, but what is important is that there is meaningful information that can be used to accomplish something encoded in that language.

If someone knows your language, you can transmit your information to them. You can use mechanical signals (such as a telegraph), electronic signals (such as a copper wire), or electromagnetic (i.e., light) signals, such as the antenna to the right, to transmit information. If you use a mechanical or electronic signal, the information transmitted always travels slower than light. If you use an electromagnetic signal, the information travels at the speed of light.

But quantum mechanics does weird things, and one of the weirdest is a phenomenon known as quantum entanglement. What this means is that two particles can have their quantum states interrelated; if you measure the state of one, you know the state of the other, but until you measure one, they’re both undetermined. This is like a double Schrodinger’s Cat paradox, except when you open the box, you find out whether your cat is dead or alive, and instantly know whether the entangled cat that you haven’t looked at is dead or alive, too. Here’s the kicker: you don’t find out whether the entangled cat is dead or alive at any given speed. You find out instantly.

In reality, this experiment doesn’t work with cats and whether they’re dead or alive, but with entangled photons and their spins (whether their spins are +1 or -1). You know the sum of their spins, but you don’t know the individual spins until you measure them. Experiments have separated the photons by miles before measuring one, and then instantly knew the spin of the other one, even though it was miles away.

So, what does this mean? Is information being passed instantly, or faster than the speed of light? Maybe; I’m not entirely sure. Because you’re learning something about the spin of a particle faster than the speed of light, and the particle starts acting like a particle of definite spin (either +1 or -1) rather than an indeterminate wave-like state, and it starts doing that instantly. But is that a transfer of useful information? I’m not sure. If it is, then it is certainly happening at superluminal speeds (at least 30,000 times faster than the speed of light). I wonder what she has to say about this:

If I send you the entangled photon and then I measure mine and you measure yours, we’ll never both see +1 or both see -1, we’ll always have opposite answers. And yet, there’s no way that the two photons can communicate with each other to tell one another what their spins are.

What can this be used for? Possibly for quantum cryptography. If I send you an entangled photon, and I use the measurement of my photon to figure out what yours is, I can use mine as an encryption key. Only you, who knows what my photon is doing because of the entanglement, will be able to decrypt it. And you’ll know the decryption key before you even get the encrypted message, because you get it instantly. Is this an instantaneous transfer of information? I think it is — do you?

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