Information, gravity and black holes

"Black holes are critical to understanding how information is represented in our universe and that the way our universe appears to be may be just a projection of a deeper reality that is pure information."

"The universe at these scales has no information except on the surfaces of black holes. And if that is true, then perhaps we are looking at spacetime and gravity backwards, and it is an effect of this information rather than a cause"

"It is meaningless to talk about gravity as a force because it is simply a holographic representation of information"

 Tim Andersen. Empty black holes may be the information storage units of the universe Medium 12 April 2023

Randomness is nothing. Nothingness is random.

To say that something is random is to say that it conveys no information. That is the true nothing.

We know from physics that vacuums, as the complete absence of any matter or energy, don't exist, because the uncertainty principle allows particle-antiparticle pairs to appear spontaneously provided they vanish again quickly enough. This is what creates the 'vacuum energy' and is measurable.

So you might argue that there's no such thing as nothing, but the presence or absence of matter or energy is of no significance. What is important is information. In the data-information model, information cannot be extracted from completely random data. Or, to put it another way, completely random data is no data at all (is nothing).

However, randomness is relative. If I listen to someone speaking a Chinese language the words are random to me because I cannot extract meaning from them, but of course they are not random to a Chinese speaker. So, nothingness is relative. Unless, that is, there exists randomness that is absolutely random. Is this the randomness of quantum mechanics? Is this 'God playing dice' (in the famous phrase of Alfred Einstein)?

Is the information of physics 'about' anything?

The New Scientist has been talking about reality again, and concludes:

"But to Susskind [Leonard Susskind of Stanford University] at least, the idea that reality might be rooted in 0s and 1s is poetically beautiful. Perhaps, he says, we will one day be able to sum up the universe in a simple epigram: “ah, everything is information”".

Anil Ananthaswamy "Essence of reality: Hunting the universe’s most basic ingredient" 1/2/2017 

Note, though:

"[T]he sort of quantum information that might underlie space-time must be a little different [from Shannon information]. The information in a stream of words is about something. By contrast, the quantum information from which space emerges in Carroll’s [Sean Carroll of the California Institute of Technology] work is just there. “The quantum state is not of or about anything,” says Carroll. 

One of the ongoing issues in information research is whether a unified theory of information (UTI) is possible. I've recently been thinking of it in terms of a unified narrative of information: an agreed way of talking about information, and trying to come up with the things we can say about whatever it is we are calling information. One of those things seemed to be that it is always about something. (Though we have to be careful about what it means to 'be about' something. I think my trapeziums help.)  So, here's a question: could it be that the physicists are wrong? Could it be that even their information is about something? Could it be that in order to understand 'reality' you need a type of information that is about something? Could it be that they are missing something?

Anyway, here's a fuller quote from the New Scientist article.

It is all very well to suggest that space and time are made of quantum entanglement and possibly quantum complexity – but what are they made of? Here is where we edge closer to finding the true bedrock of reality. Because both approaches suggest the same tantalising answer: information.

The mathematician and engineer Claude Shannon gave us a neat way to define information in 1948. He showed that the amount of information in something like a stream of bits or letters is related to its entropy, a measure of disorder. The greater the entropy, the greater the information. For example, a stream of three-bit numbers that are always 000 contains less information than a stream in which the numbers can also be 001, 101 or 111.

So in what sense is information at the root of things? Well, entanglement is information: the greater the entanglement between two systems, the more information they share. But there’s a caveat. The information Shannon defined certainly seems to exist and has real effects. Experiments just last year showed a nanomachine could use information to chill metal. But the sort of quantum information that might underlie space-time must be a little different. The information in a stream of words is about something. By contrast, the quantum information from which space emerges in Carroll’s work is just there. “The quantum state is not of or about anything,” says Carroll. “It is simply our best mathematical description of the universe.”

It actually makes sense that quantum information would be the foundation everything is built on, says Carroll. If you start with quantum mechanics and don’t presume anything else exists, then “basically all you have to play with is quantum information”. That would make information a basic constituent of the universe. “You can find people who think that information is all there is,” says Carroll.

Information-tinted spectacles solving the problems of physics

"Perhaps looking at the universe through information-tinted spectacles will open us up to blindingly obvious solutions that make the problems we encounter today melt away."

I do wish the New Scientist would stop claiming they are talking about reality. It is hype to claim authority over all other human endeavour.

Nevertheless, this: "Six Principles / Six Problems / Six Solutions" (New Scientist, 24 September 2016 pp28 -35) is great. They call it 'The Nature of Reality' on the cover (and "The Structure of Reality" on the poster), but what it really (!) is, is an overview of the state of physics.  They have put it together as a poster you can download from here bit.ly/physicsposter (which I have done, printed out, and put on the side of a filing cabinet in my office.)

It starts from what they call on the cover "six principles that rule the universe' but inside the magazine are, more reasonably, "six basic principles that underlie our theories of physics on scales large and small". It follows these through to six problems and then to six (possible) solutions. So:

Six principles
THE SPEED OF LIGHT IS A CONSTANT. Nothing can exceed this cosmic speed limit
THE EQUIVALENCE PRINCIPLE . Gravity and acceleration always look the same
THE COSMOLOGICAL PRINCIPLE. The universe is the same in all places and in all directions
QUANTISATION. Things come in bite-size chunks
UNCERTAINTY. There’s a limit to how much any of us can know
WAVE-PARTICLE DUALITY. Quantum objects exist in many different guises at once

Six problems
DARK MATTER. Galaxies rotate too quickly for their visible matter
DARK ENERGY. The universe is flying apart faster and faster
INFLATION. Faster-than-light expansion spawns many other universes
FORCE UNIFICATION. Our theories of reality don’t get along
FINE-TUNING. We can’t explain the numbers that rule the universe
MEASUREMENT. Do we inadvertently control everything that happens?

Six solutions
MODIFIED GRAVITY. Our theories of gravity have only ever been tested on small scales
SUPERSYMMETRY. More particles can explain why the universe is as it is
FIFTH FORCE. Could a quintessence banish cosmic ghosts?
STRING THEORIES. An ultimate theory must subsume quantum theory and relativity
THE MULTIVERSE. The universe is as it is – because every other universe is out there too
INFORMATION. Energy and matter don’t matter – information is where it’s at

And there we have it, at the bottom: information might be the solution! 

INFORMATION.

Energy and matter don’t matter – information is where it’s at

When attempting to unify general relativity and quantum theory, it’s generally assumed that general relativity is at fault. It is, after all, a classical field theory of the sort that shinier quantum theories have otherwise nudged aside.

But as long as aspects of quantum theory such as the measurement problem remain largely inexplicable, there’s always the chance it is the wrong’un, or just an approximation to some deeper theory. What’s truly pulling the strings of entanglement, for example? The world embodied by quantum theory is not the most entangled world out there – other, even weirder worlds exist in theory that have even greater degrees of correlation. Why this entangled, and not more?

That might be another fine-tuning issue. But entanglement does seem to be at the root of many mysteries, and there are recent hints that it could be the warp and weft that holds space and time together. In that case, what is entanglement? The best we can say is that it’s some sort of collective information shared between particles.

That highlights a common theme in much cutting-edge physics: that understanding space-time, and the route to a more unified picture of nature generally, lies in treating information – not matter and energy – as the most fundamental thing in the universe and understanding better how it works.

Perhaps looking at the universe through information-tinted spectacles will open us up to blindingly obvious solutions that make the problems we encounter today melt away.

Precisely!

How information helps to banish quantum weirdness - the fivefold way.

One of the strands in the current excitement about information is that it can provide a narrative for explaining our experiences of the world* that does away with the mental contortions that other scientific narratives demand. An easy example - or rather the one I find most useful - is that you can stop worrying about 'spooky action at a distance' if no information is communicated faster than the speed of light (see my past posts on the EPR paradox).

* The New Scientist would spin it by saying 'explaining reality' but I think I am a reality-agnostic. Anyway, I don't like word.

More generally, a number of narratives are developing that are more of less 'grand'.

Quantum purity: How the big picture banishes weirdness

Anil Ananthaswamy

We have become accustomed to the universe blowing our minds – perhaps too accustomed. Quantum weirdness – things like particles being in two places at once, or appearing to share a telepathic link – has been baffling us for more than a century now. The physicist Richard Feynman once said that nobody really understands the quantum world. Or as others have put it: if you think you understand it, then you definitely don't. So it is tempting to throw up our hands and say human brains can never grasp it.

But maybe we shouldn't be so defeatist. Isn't it just possible that we simply haven't yet got to the bottom of how quantum mechanics really works? That's what Giacomo Mauro D'Ariano of the University of Pavia in Italy, and his colleagues Giulio Chiribella and Paolo Perinotti think – and they have been doing something about it. They have come up with a non-weird foundation from which all quantum weirdness can arise.

Ananthaswamy goes on to draw parallels from scientific history, of how we had descriptions of the world that worked but seemed arbitrary until we later found an underlying principle that help it all together.

Kepler's laws of planetary motion worked but were arbitrary until underwritten by Newton's universal law of gravity. Lorentz's equations were ad-hoc solutions to accommodate contradictory experimental observations about the speed of light until Einstein proposed some physical principles – that the speed of light in a vacuum is constant and independent of the motion of the source of light – from which he was able to derive Lorentz's transformations

"When I look at quantum theory, I see something that's akin to the ad hoc nature of Kepler's laws of planetary motion and of Lorentz transformations," says Hardy [Lucien Hardy of the Perimeter Institute in Waterloo, Canada]. "What we need is some deeper set of principles."

In the early 2000s, Hardy made his own attempt at coming up with some. It wasn't a full solution, he admits, but it inspired D'Ariano, Perinotti and Chiribella to dig deeper. "The idea was to somehow reprogram the genetic code of quantum mechanics, choose some physical properties and say, 'this is the fundamental thing', and re-derive the rest from it," says Chiribella, who is now at Tsinghua University in Beijing, China.

For both Hardy and D'Ariano's team, the "fundamental thing" has to do with information.

[...]

Eventually, they came up with five fairly common-sense ideas that worked: things like ensuring the future can't influence the past

Here are those five ideas:

Causality
Stuff in the future cannot affect a measurement you're making right now.

Distinguishability
If a state is not too noisy, then there exists another state that can be distinguished from it.

Composition
If you know everything it is possible to know about all the stages of a process, then you know everything you can about the whole process.

Compression
There are ways to efficiently transmit all the information relevant to a measurement of a physical system without having to transmit the system itself.

Tomography
When you have a system with several parts, the statistics of measurements carried out on the parts is enough to identify the state of the whole system.

Applications of Maxwell's demon

A couple of items about experiments based on 'Maxwell's Demon', using information to extract energy from the environment and (at first sight) violating thermodynamics. ('Heard through' a post by John Collier on the FIS email discussion group.)

Physicists Convert Information Into Energy

The first demonstration of an information-heat engine could revolutionise the way nanomachines get their power.

[Japanese physicists created a kind of staircase in which they lowered an energy barrier to allow atoms to jump up a step and then raised it to prevent the atom falling back down again.

As a result, the atom slowly climbed the staircase even though no energy was added to the system.]

MIT Technology Review, September 30, 2010

And

Entangled Particles Break Classical Law of Thermodynamics, Say Physicists

Japanese physicists show how to extract more energy from entangled particles than is possible with classical thermodynamics

MIT Technology Review, September 30, 2012

Constructor Theory: David Deutsch et al.'s new (information) theory of everything

In the current issue (24 May 2014) of New Scientist is another opinion piece from David Deutsch and Chiara Marietto on their 'Constructor Theory'.

WHEN we consider some of the most striking phenomena permitted by the laws of physics – from human reasoning to computer technologies and the replication of genes – we find that information plays a central role. But, on the face of it, information is profoundly different from the basic entities that physical sciences use to describe reality. Neither quantum mechanics nor general relativity, the most fundamental theories in physics, provide a meaning for information or even a way of measuring it. And it has a "counterfactual" character: a message cannot carry information unless a different message is also possible.

Statements about information were therefore long regarded in physics as second-class, non-fundamental approximations. Information itself was considered an a priori abstraction, like Euclid's perfect triangles and circles, whose physical instantiations are inevitably approximate. [...]

[Constructor theory] makes knowledge creators, such as people, central to fundamental physics for the first time since Copernicus debunked the geocentric model of the solar system.

Reconstructing physics: The universe is information

A good place to find more about constructor theory is a video interview (with transcript) that Deutsch did a couple of years back: here CONSTRUCTOR THEORY. A Conversation with David Deutsch

It's 47 minutes long and covers a lot ground, both introducing the theory and talking extensively about why he's doing it and more general thoughts on science and philosophy. For my own present concerns, there's a couple things I'll pick out.

Firtly, his speculation that cybernetics was a precursor of constructor theory:

I'm not very familiar with the very popular idea of cybernetics that came about a few decades ago, but I wouldn't be surprised if those ideas that proved at the time not to lead anywhere were actually an early avatar of constructor theory. If so, we'll only be able to see that with hindsight, because some of the ideas of constructor theory are really impossible to have until you have a conceptual framework that is post quantum theory of computation, i.e., after the theory of computation has been explicitly incorporated into physics, not just philosophically. That's what the quantum theory of computation did.

Secondly, the scope he is claiming for the significance of the theory. He is claiming that the theory delivers 'optimism', with the specific claim that it shows that "all problems and all evils are caused by lack of knowledge, and the converse of that is that all evils are soluble given the right knowledge".

[T]here is one big thing that I'm pretty sure the constructor theoretic way of looking at physics has to offer our worldview in terms of everyday life: and that is optimism. Optimism in my terminology doesn't mean expecting that things will turn out well all the time. It's this very specific thing that I think captures the historical, philosophical trend of what optimism has meant if you remove the nonsense. Namely, the optimistic view is not that problems will not occur, but that all problems and all evils are caused by lack of knowledge, and the converse of that is that all evils are soluble given the right knowledge.

Heinz von Foerster: "how interesting is the story"

Heinz von Foerster.

"All that is relevant, is how interesting is the story". It makes me think of "Life of Pi".

The surprise theory of everything

Vlatko Vedral writing in the New Scientist.

In this essay, I will explore the fascinating question of why, since their origins in the early 19th century, the laws of thermodynamics have proved so formidably robust. The journey traces the deep connections that were discovered in the 20th century between thermodynamics and information theory - connections that allow us to trace intimate links between thermodynamics and not only quantum theory but also, more speculatively, relativity. Ultimately, I will argue, those links show us how thermodynamics in the 21st century can guide us towards a theory that will supersede them both.

The surprise theory of everything - physics-math - 15 October 2012 - New Scientist

(Prof Vedral was one of the Keynote Speakers at "The Difference That Makes a Difference 2011" - see his presentation here)

Information Theory "proves" the uncertainty principle

Or rather, it helps with an intuitive justification of the uncertainty principle, which is what the authors were seeking, and, maybe, suggests the search for 'hidden variables' explanations of the uncertainty principle are unlikely to succeed.

From the New Scientist 23rd June 2012:

Stephanie Wehner and Esther Hänggi at the National University of Singapore's Centre for Quantum Technology have taken a new tack, recasting the uncertainty principle in the language of information theory.

First, they suggest that the two properties of a single object that cannot be known simultaneously can be thought of as two streams of information encoded in the same particle. In the same way that you can't know a particle's momentum and location to an arbitrarily high level of accuracy, you also can't completely decode both of these messages. If you figure out how to read message 1 more accurately, then your ability to decrypt message 2 becomes more limited.

Next the pair calculate what happens if they loosen the limits of the uncertainty principle in this scenario, allowing the messages to be better decoded and letting you access information that you wouldn't have had when the uncertainty principle was in force.

Wehner and Hänggi conclude that this is the same as getting more useful energy, or work, out of a system than is put in, which is forbidden by the second law of thermodynamics. That is because both energy and information are needed to extract work from a system.

To understand why, imagine trying to drive a piston using a container full of heated gas. If you don't know in which direction the gas particles are moving, you may angle the piston wrongly and get no useful work out of the system. But if you do know which way they are moving, you will be able to angle the piston so that the moving particles drive it. You will have converted the heat into useful work in the second scenario, even though the same amount of energy is available as in the first scenario.

Being able to decode both of the messages in Wehner and Hänggi's imaginary particle suddenly gives you more information. As demonstrated by the piston, this means you have the potential to do more work. But this extra work comes for free so is the same as creating a perpetual motion machine, which is forbidden by thermodynamics (arxiv.org/abs/1205.6894v1).

"The second law of thermodynamics is something which we see everywhere and basically no one is questioning," says Mario Berta, a theoretical physicist from the Swiss Federal Institute of Technology in Zurich, who was not involved in the work. "Now we know that without an uncertainty principle we could break the second law."

Jessica Giggs "To be quantum is to be uncertain", New Scientist v214 n2870 (online here)

Absence of information is the real nothing; not absence of stuff

The current New Scientist is a Special Issue on 'Nothing'. They've got five articles linked to the theme:

1. From zero to hero. About the history of the mathematical symbol for '0', and the mathematical concept of zero.
2. Nothing in common. Building maths starting from the concept of the empty set
3. The hole story. How the concept of a 'hole' as a positively-charged particle rather than just the absence of an electron was crucial to the development of solid-state electronics
4. Out of the ether. Vacuum field - how quantum mechanics leads to the understanding that a vacuum is actually seething with particles emerging and disappearing
5. Putting the ideal to work. The discovery and value of Noble gases.

An interesting topic (though already pretty familiar to most readers of the New Scientist, I would have thought), but there's nothing there about information - they've missed the big story again!

It is the absence of information that is the real nothing, not the absence of stuff.  It is similar to what I was saying about going faster than light. Stuff (matter/energy) only has any significance insofar as it carries information. A complete 'grey death' of the universe (thermodynamic equilibrium over the whole universe) would be a real nothing.

Like so much on this blog, I've got ideas about this, but other people have explored nothing and information much more rigorously.

Vlatko Vedral and Rainer Zimmermann talking about nothing. 

At DTMD 2011, Vlatko Vedral introduced some of his ideas on how informational thinking provides insights into the fundamental question of how something comes from nothing. You can pick up his presentation from the DTMD 2011 proceedings page (or directly: Abstract Presentation Podcast). Vedral, though, was challenged by Rainer Zimmermann, one of the other delegates at the workshop, during the panel session after Vedral's presentation, and you can listen to that too: Panel Discussion (42 MByte mp3 file). Specifically, Zimmermann, says

I find the categories of nothingness and non-being mixed up...so the consequence is that your God metaphor and also your card game is not correct because it is not demonstrating what you would like to demonstrate. For instance saying that God himself would not know entails that you think of the assembly of knowledge for God, or substance, or whatever you would like to call it, in an anthropomorphic way, but it is obviously not logical at all. That is actually an idea going back to Spinoza in the seventeenth century. On the other hand, the card game is not telling anything about nothingness, because what you actually show is that if you discard the means of representation in favour of another means for instance by skipping the cards and doing that in an abstract way, for instance playing blind chess..., you are not actually doing anything ontological, all you do is switch the means of representation, so in fact there is not nothingness but it is quite a lot.  Independent of the case nothingness in philosophical terms is not nothing, that is the point, it is actually the foundation of non-being. And non being is what is not but could be, it's a possibility. We had that already earlier in the keynote of Hofkirchner's field of possibilities and nothingness is the foundation of non-being. By coincidence on Friday afternoon I will give a talk on nothingness at the University of London...

(I've kept the reference to his University of London talk to point to the fact that he - Zimmermann - has been researching nothingness.  I need to find out more!)

Talk of non-being, field of possibilities, what could be, puts me very much in mind of Rubem Alves writing in The Poet, the Warrior, the Prophet of how the discovery of a dead body of man has all sorts of consequences precisely because he is dead - because he is not there (I referred to this in passing once before). However, I am aware I'm on shaky ground there, and I'm not sure Dr Zimmermann would approve!

Those neutrinos travelling faster than light

Amplify’d from www.scientificamerican.com

An Italian experiment has unveiled evidence that fundamental particles known as neutrinos can travel faster than light. Other researchers are cautious about the result, but if it stands further scrutiny, the finding would overturn the most fundamental rule of modern physics—that nothing travels faster than 299,792,458 meters per second. [...]

The idea that nothing can travel faster than light in a vacuum is the cornerstone of Albert Einstein's special theory of relativity, which itself forms the foundation of modern physics. Read more at www.scientificamerican.com

See this Amp at http://bit.ly/ozVWVZ

This claim that 'nothing can travel faster than light' is sloppy, because you have to interpret what counts as a 'thing' in the word 'nothing'.

There's no problem at all with a phase velocity being faster than the speed of light. For example, an interference pattern can easily 'travel' faster than light, and the pattern might look like a 'thing'. Just think of two plane waves propagating at v and crossing at a shallow angle (say theta), then the intersection of the wavefronts 'travels' at a speed vp where vp = v/sin(theta/2). (I need for find an image of this). By making theta small vp can be as big as you like.

In a waveguide (such as an optical fibre) this is the phase velocity, but the more meaningful speed is the group velocity vg.  The group velocity is the speed at which information can be transmitted, and is always less than v. In fact vg x vp = v^2.

My point is that the 'thing' that can't travel faster than light is information, which is the point I made before about the EPR paradox.

Of course all this probably irrelevant as far as the neutrino story is concerned. If particles are travelling faster than light and being detected, then presumably information could be transmitted using them.  Still, it seemed like that at first sight with the EPR paradox yet when you analyse it carefully (which is way beyond my understanding but has been done by people who know) it turns out that you can't actually use it to send information faster than the speed of light.

My bet is that whatever the resolution of this latest neutrino story, it'll turn out that you can't send information faster than light. 

Quantum Biology

I like that "Biology has a knack for using what works".

Amplify’d from www.nature.com

On the face of it, quantum effects and living organisms seem to occupy utterly different realms. The former are usually observed only on the nanometre scale, surrounded by hard vacuum, ultra-low temperatures and a tightly controlled laboratory environment. The latter inhabit a macroscopic world that is warm, messy and anything but controlled. A quantum phenomenon such as 'coherence', in which the wave patterns of every part of a system stay in step, wouldn't last a microsecond in the tumultuous realm of the cell.

Or so everyone thought. But discoveries in recent years suggest that nature knows a few tricks that physicists don't: coherent quantum processes may well be ubiquitous in the natural world. Known or suspected examples range from the ability of birds to navigate using Earth's magnetic field to the inner workings of photosynthesis — the process by which plants and bacteria turn sunlight, carbon dioxide and water into organic matter, and arguably the most important biochemical reaction on Earth.

Biology has a knack for using what works, says Seth Lloyd, a physicist at the Massachusetts Institute of Technology in Cambridge. And if that means "quantum hanky-panky", he says, "then quantum hanky-panky it is". Read more at www.nature.com

 

See this Amp at http://bit.ly/miiGGB

Detecting Schrödinger’s half-dead cat

I'd thought it was theoretically impossible to do this, not just impractical.

Amplify’d from www.newscientist.com

IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.

In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.

Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.

The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).

Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."

Carrying out this experiment is still a few years away Read more at www.newscientist.com

See this Amp at http://bit.ly/lbLJ7i

A point has no physical significance

A quotation I want to keep hold of:

I maintain that the mathematical concept of a point in a continuum has no direct physical significance. It has no meaning to say the value of a coordinate x... has a value x = sqrt(2) in. or x = π cm. [...]

Modern physics has achieved its greatest successes by applying the methodological principle that concepts which refer to distinctions beyond possible experience have no physical meaning and ought to be eliminated … The most glaringly successful cases are Einstein's foundation of relativity based on the rejection of the concept of aether ... and Heisenberg's foundation of quantum mechanics .. I think that this principle should be applied also to the idea of physical continuity

Max Born, quoted in Brillouin (1962, p303). Though I'm wondering whether this is any more true of irrational than rational numbers. A coordinate of 2 cm is just as much a point in a continuum as π cm, is it not?

Brillouin, L.

Science and Information Theory

Academic Press, 2nd ed. 1962

Understanding physics, or not.

I feel as though I understand this. That is to say, I can see how these stories might be explaining things.

The concept of quarks and gluons are in some sense 'reasonable' and I can imagine relativistic calculations on their energies, and cross-sections derived from the wave-functions of quantum mechanics. Of course I can't do those calculations, but I believe they can be done and I can see that in doing them they would explain the measurements (and thereby 'carry' some sort of understanding of the world).

I say this, because it is in contrast to anything I've read about string theory. I have just never got any sort of grip on what string theory is doing. I don't know whether this says something about me - perhaps to do with when I did my physics degree - or about string theory, or about the people who write about string theory, or about the nature of understanding.

It is probably about all of those thing, but it bothers me.

Amplify’d from www.guardian.co.uk

Quarks, gluons and jets

The LHC paper I've been working on for the past few months is finally out. It shows quarks and gluons doing what they should do, and I love it

When we collide protons, we really care most about the collisions between the proton's constituents - quarks or gluons. Unfortunately the quarks and gluons only carry a fraction of the energy of the proton, and we have no way of choosing how much. If the fraction was a half, for example, then we would have jets with 1750 gigaelectronvolts (GeV) of energy (half of 3.5 TeV). But most of the quarks and gluons carry much smaller fractions.

To have a real measurement of this, and show that the theory prediction (quantum chromodynamics, labelled QCD on the plot) agrees with the data, is a real achievement. It directly involved dozens of people, and less directly hundreds. One key component is the energy calibration which I described here. Read more at www.guardian.co.uk

 

See this Amp at http://bit.ly/cgW5OQ

EPR paradox

Here's my understanding of the paradox (the story I tell myself about it), and why in terms of information there's no problem.

(I'm writing this from memory, so it could be rubbish, but I think I have some of the essence in here. And it's not the original EPR - Einstein, Podolsky and Rosen - formulation, which I think was based on beta decay.) Imagine launching two entangled particles, say photons, heading off to two different locations. You take a measurement on one of them, say you test for spin up or down. The result of the measurement on one immediately tells you the result you'll get on taking the same measurement on the other. Eg, you measure photon A and find spin up, so you know measuring photon B will give you spin down. OK, no big deal so far. But, quantum mechanics tells you that photon A didn't decide it was going to be spin up until you measured it. So photon B has to be told, instantaneously, what photon A had decided to give as its result. Hence the need for instant communication (faster-than-light = violates causality, 'non-localisation')

But, as explained so far, it is pretty unconvicing to say that photon A didn't decide on what result it was going to give until it was measured. There's more to it. Instead of measuring for spin up or down, you could instead measure another parameter, say for spin rotation, clockwise or anticlockwise.* If you measure for spin rotation, then if A is clockwise B will measure anticlockwise and vice versa. But, if you measure for rotation then you lose coherence (is that how to express it?) for spin up or down. So, if you measure A for rotation, B can now be spin up or down with equal probablity. Likewise if you measure A for up or down, B can be closkwise or anticlockwise with equal probability. So now what is happening is that A 'tells' B whether you measured for rotation or up/down (as well as the result). Again, it has to happen instantaneously, hence the contradiction with relativity.

Experiments have been done, apparently, which test for this - the effect that measuring A influences the outcome of measurements on B. Now, I have not yet got an understanding of how these experiments are done. I'd love to know. But, my understanding of the conclusions of the experiments is:

- they have proved that there is an influence at a distance that happens faster than the speed of light
- but, you can not communicate information faster than the speed of light in this way

Now, here's my punchline: that final point somehow ruins it all! If you are not communicating information, then what's the big issue? Surely it is just like phase velocity in, say, waveguides? There's no problem at all with phase velocity exceeding c, because you can't carry information on the phase. It is the group velocity that matters.