This is water

...what if space — perhaps at something like the Planck scale — is just a plain old network, with no explicit quantum amplitudes or anything? It doesn’t sound so impressive or mysterious — but it certainly takes a lot less information to specify such a network: you just have to say which nodes are connected to which other ones. 

But how could this be what space is made of? First of all, how could the apparent continuity of space on larger scales emerge? Actually, that’s not very difficult: it can just be a consequence of having lots of nodes and connections. It’s a bit like what happens in a fluid, like water. On a small scale, there are a bunch of discrete molecules bouncing around. But the large-scale effect of all these molecules is to produce what seems to us like a continuous fluid.

What is space-time really? Stephen Wolfram

Harlequin ghost pipefish from underseaimages

Shadows of the sky

Thinking about neutrinos, I also came across this:

This light tells us much, but I think in the course of time still more delicate and subtle mediums will be found to exist, and through these we shall see into the shadows of the sky. 

Photo NSF / B. Gudbjartsson via APOD

Big

The Copernican principle states that, on the large scale, the universe is homogenous and is nowhere special.  But it is reported that at least three phenomena call that into question:

A void almost 2 billion light years wide called the CMB coldspot. 

A structure strung out over 4 billion light years containing 73 quasars known as the Huge Large Quasar Group. 

A group of gamma-ray burst emitting galaxies that form a ring 5.6 billion light years across – 6% of the size of the entire visible universe.

Some physicists argue that these phenomena may be evidence for brane theory — the idea that what we perceive as our universe is a single four dimensional membrane floating in a sea of similar (mem)branes spanning multiple extra dimensions.

Image via Daily Galaxy

A new idea of reality

Richard Feynman once suggested that nature is like an infinite onion. With each new experiment, we peel another layer of reality; because the onion is infinite, new layers will continue to be discovered forever. Another possibility is that we’ll get to the core. Perhaps physics will end someday, with the discovery of a “theory of everything” that describes nature on all scales, no matter how large or small. We don’t know which future we will live in. But the observation of neutrino masses tells us that the adventure of discovery in which we are currently involved will not end here. There are still fundamental mysteries to be resolved.

What Neutrinos Reveal Lawrence Krauss


Photo of Wolfgang Pauli via flickr

'On the edge of what we know...'

The heat of black holes is a quantum effect upon an object, the black hole, which is gravitational in nature. It is the individual quanta of space, the elementary grains of space, the vibrating 'molecules' that heat the surface of black holes and generate black hole heat. This phenomenon involves three sides of the problem: quantum mechanics, general relativity and thermal science. The heat of black holes is like the Rosetta Stone of physics, written in a combination of three languages — Quantum, Gravitational and Thermodynamic — still awaiting decipherment in order to reveal the true nature of time.

Carlo Rovelli

Image via wikipedia

Miracle enough

My wife and I spend summers on a small island in Maine, far from any town. At night, the skies are quite dark. Sometimes, when there is no wind blowing and the tidal flow is small and the ocean is very still, I can see the reflection of the stars in the water near our dock. At such moments, the water looks like a dark carpet with a million tiny sparkles of light, which gently bob and ripple with each passing wave. Even though I know all the science, I am totally mesmerized and awed. For me, that is miracle enough.

Splitting the Moon Alan Lightman

'A vacuum is never really empty'

In... quantum field theory, a vacuum is never really empty... It is an arena in which quantum fluctuations produce evanescent energies and elementary particles. 

These short-lived phenomena might seem to be a ghostly form of reality. But they do have measurable effects, including electromagnetic ones. That’s because these fleeting excitations of the quantum vacuum appear as pairs of particles and antiparticles with equal and opposite electric charge, such as electrons and positrons. An electric field applied to the vacuum distorts these pairs to produce an electric response, and a magnetic field affects them to create a magnetic response. This behaviour gives us a way to calculate, not just measure, the electromagnetic properties of the quantum vacuum and, from them, to derive the value of c.

Why is light so fast? Sydney Perkowitz

Black Square by Kazimir Malevitch. Tate

Randomly different initial conditions

Modern cosmology involves the idea of quantum genesis — tracing back the cosmic expansion to an origin in a singularity where the space that now contains 100 billion galaxies was smaller than an atom. The inflationary scenario is an adjustment of standard big bang to include an extremely early phase of exponential expansion. The idea was developed to explain why the universe now is very smooth and geometrically flat. Inflation has tentative support from the nature of small temperature variations in cosmic background radiation. If inflation is correct, the universe began as quantum fluctuation. The precursor state would have been an ensemble of quantum fluctuations, perhaps infinite in number, each with randomly different initial conditions. Some of them inflated into large space-times like our own. Others were still born. This process can be timeless and eternal.

Beyond: Our Future in Space by Chris Impey (2015)

Light passes through light...

Light passes freely through light. Were that not true, the visual messages we receive from the world would be scrambled by scattering, and much more complicated to interpret. In QED, that basic fact makes good sense: photons respond to electric charge, but photons themselves are electrically neutral.

A Beautiful Question by Frank Wilczek (2015)

Photo by author

Musica universalis

The equations for atoms and light are, almost literally, the same equations that govern musical instruments and sound.

Frank Wilczek, A Beautiful Question (2015)

Any-angled light

A photon at the centre of the Sun may collide with atoms between about 49 billion trillion and 49 trillion trillion times before it reaches the surface. Even moving at the speed of light between collisions that will take from around five thousand to half a million years.

Sunshine's Crazy Sloppy Path to You by Robert Krulwich

Ars Nova

It will be fruitful, and great fun, to use modern resources of signal processing and computer graphics to translate the beautiful concepts and equations of physics into new forms of art. Then, physicists will be able to bring their visual cortices fully to bear on them, and people in general will be able to admire and enjoy them. In the future, artists and scientists will work together more together, and create new works of extraordinary beauty... 

Artificial intelligence...offers strange new possibilities for the life of mind. An entity capable of accurately recording its state could purposefully enter loops to relive especially enjoyable episodes, for example. A quantum mind could experience the superposition of “mutually contradictory” states or allow different parts of its wave function to explore vastly different scenarios in parallel. Being based on reversible computation, such a mind could revisit the past at will and could be equipped to superpose past and present.

How Physics Will Change—and Change the World—in 100 Years by Frank Wilczek

In a longer version of the article (pdf), Wilczek adds:

I have described a future in which people know much more about, and have vastly greater power over, the physical world than we do today. Paradoxically, perhaps, I think that this will make them more sensitive to gaps in their knowledge, and ambitious to accomplish more...Such emergent humility reflects not so much modesty, as largeness of vision.

Image via APOD

wild Abyss

Amy Leach writes

A star will not shine until it has assembled enough self [and] once it has enough self it cannot help but shine; once it starts to shine it cannot help but burn the self up and blow the self away upon the stellar winds.

The star system PSR J0348+0432 consists of a white dwarf and neutron star 830,000 kilometres apart --about twice the distance from the Earth to the Moon. They orbit around each other once every 2 hours and 27 minutes. at a velocity of about 2 million kilometres per hour. The neutron star is about 26 kilometres in diameter and has mass is twice that of the Sun. It spins on its axis about 25 times a second.  Gravity here is over a hundred billion times its value on Earth.

General Relativity predicts, and measurements confirm, that the two stars will spiral in towards each other, emitting gravitational waves.

A white dwarf that is not caught in such a system may continue to exist almost indefinitely – or at least 10³² years. Eventually, it may turn into a black dwarf. None of these exist yet because their precursors would have to be older than the universe.

Image: ESO/L. Calçada

Goes Boink

Scientific progress...is often triggered by rather innocuous discoveries or simple realisations. There is a terrible cliché about scientists exhibiting a ‘childlike’ fascination with nature, but I can’t think of a better way of putting it. The sense in which the cliché rings true is that children are occasionally in the habit of focusing on a very small thing and continuing to ask the question ‘Why?’ until they get an answer that satisfies their curiosity. Adults don’t seem to do this as much. Good scientists do, however, and if I have a thesis...it is as follows: by focusing on tiny but interesting things with honesty and clarity, great and profound discoveries are made, often by flawed human beings who don’t initially realise the consequences of their investigations.

The Human Universe by Brian Cox and Andrew Cohen (2014)

'On the materiality of colour'

Here are some images relating to Materiality of Colour: from Neolithic Earth Colours to Contemporary Interference Pigments, a seminar convened by Antoni Malinowski.

This is pigment timeline discussed by Jo Volley and colleagues from UCL (see note [1])

Here is an image that uses Indian Yellow, one of the pigments discussed by Ruth Siddall. Traditionally, this was made from the boiled urine of cattle fed exclusively on mango tree leaves.

This is the colour library in Venice, described by Malinowski as one of his favourite places

And this is from a Color-coordinate system from a 13th-century account of rainbows by Hannah Smithson et al. [2]

Notes

[1] I have turned the image upside down so that the present time is at the top and the lower down you go the further back in time you go. This is to reflect an idea, expressed at the seminar, that the pigments 'arise from the earth'

[2]  Historical European models of the spectrum can be found here or here

Pattern, process and change

In creating [a mathematics of flowing quantities and rates of change] Newton embraced a paradox. He believed in a discrete universe. He believed in atoms, small but ultimately indivisible - not infinitesimal. Yet he built a mathematical frameworks that was not discrete but continuous, based on a geometry of lines and smoothly changing curves... 

Here at Woolsthorpe the night was strewn with stars, the moon cast its light through the apple trees, and the day's sun and shadows carved their familiar pathways across the wall.  Newton understood now: the projection of curves onto flat planes; the angles in three dimensions, changing slightly each day. He saw an orderly landscape. Its inhabitants were not static objects; they were patterns, process and change.

Isaac Newton by James Gleick (2004)


Newton's early papers here.

Complexity

We know there's a law of nature, the second law of thermodynamics, that says that disorderliness grows with time. Is there another law of nature that governs how complexity evolves? One that talks about multiple layers of the structures and how they interact with each other? Embarrassingly enough, we don't even know how to define this problem yet. We don't know the right quantitative description for complexity. This is very early days. This is Copernicus, not even Kepler, much less Galileo or Newton. This is guessing at the ways to think about these problems.  

Layers of Reality, Sean Carroll

Image: Rhea in front of Saturn, NASA

Signposts

At a talk for non-specialists on 21 February, David Tong outlined three big problems in physics [1], which I oversimplify/misrepresent as follows:

Dark energy.  We've known for nearly a hundred years that the universe is expanding. It as if there is an antigravity force causing everything to repel everything else. We have no idea what it is. It’s 70% of the energy of the universe, it’s increasing all the time and we don’t understand it. Our best calculations are wrong by a factor of 10⁶⁰ .

Black holes.  Information that goes into a black hole is lost forever. It does not reappear in Hawking radiation. But this cannot be.

Holography. It may be that our three dimensional world is actually a mirage. The correct description will be one in which the laws of physics are written on a two dimensional surface, and the laws of physics we can see in the universe are encoded on this surface in the same way that a hologram encodes a three dimensional surface.

So, Tong concluded, there is a lot in the fundamental physics that we simply don’t understand, and that it seems unlikely we’re going to get guidance from experiment. Looking to history, however, it is precisely when there is a crisis that physics has thrived. He is optimistic about progress.


Note [1]: Some people say there are three great mysteries in science as a whole: the origin of the universe, the origin of life and the origin of consciousness.

Image: Douglas Griffin

Slow light

Not the kind explored here by Radiolab but the 'normal' kind:



Remember, however, that from the point of view of a photon, whether from the Sun or the Andromeda galaxy, what we perceive as the distance to any object is traversed instantaneously. As Jim Al Khalili puts it:

For a particle of light, time stands still, such that the past, the present and future all collapse into one eternal moment.

Blazing heart

The fact that fusion can occur in [stars] is in many ways astounding. Fusion is not simply a union of two nuclei. In most stars, hydrogen nuclei can’t get close enough to fuse. The closer a pair of hydrogen nuclei get, the more strongly their positive charges push them apart. But because nuclei are quantum objects, they don’t need to be close enough to fuse, just to be in the same ballpark. From there an effect known as quantum tunneling can do the rest. One moment the two nuclei are almost close enough to fuse, and the next moment they suddenly find themselves bonded together. It is as if the nuclei don’t have enough energy to open the door and walk through, but they occasionally will teleport through walls. 

But even this bit of quantum magic isn’t enough for a star to succeed. Not only does fusion have to occur, it has to produce something stable. When two protons fuse to become helium-2 (containing two protons and no neutrons), it is extremely unstable and usually splits right back into two separate protons. But there is a 1 in 10,000 chance that one of the protons will instead transform into a neutron, and the atom then becomes deuterium, a stable isotope of hydrogen. Deuterium and hydrogen can fuse to make a stable helium, releasing a huge amount of energy and opening up the amazing creative potential of stars.

— from How the universe made the stuff that made us by Brian Koberlein

Image: anonymous portrait of young Romanian girl (via Jane Long)