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10 years of the Physics arXiv Blog: 2008

Saturday, August 12th, 2017
The Physics arXiv Blog is 10 years old today. Over the next few days, we’ll be celebrating by publishing links to the top stories from each year of its existence.
Today, 2007.

The Physics arXiv Blog is 10 years old today. Over the next few days, we’ll be celebrating by publishing links to the top stories from each year of its existence.

Today, 2008.

Cloaking objects at a distance
Quantum communication: when 0 + 0 is not equal to 0
Do nuclear decay rates depend on our distance from the sun?
Feline ballistics
First superheavy element found in nature
Rubik’s cube proof cut to 25 moves
First test of exotic space thruster ends in explosion
Forget black holes, could the LHC trigger a “Bose supernova”?

More changes to the Physics arXiv Blog

Saturday, September 14th, 2013

From September 2013, The Physics arXiv Blog is moving to Keep up to date with the latest ideas in physics and astronomy at:

For those of you more interested in technology, I’ll be covering this at Technology Review in a blog called “Emerging Technology from the arXiv” at:

Follow the headlines on Twitter at:

See you there!

In case ya missed ‘em…

Sunday, June 29th, 2008

The cocktails from the physics arxivblog this week:

The latest social network: binge drinking

Why black holes could be antimatter factories

Surfing solves puzzle of water snail locomotion

Solar system filled with dark matter, say astronomers

The popcorn experiment and spooky action-at-a-distance

In case ya missed ‘em…

Sunday, March 30th, 2008

…this week’s peaches from the physics arXiv blog:

The wound ballistics question

How Hawking radiation may explain dark energy

Rubik’s cube proof cut to 25 moves

The curious case of the disappearing physicist

Questioning the Big Bang

Entanglement beats gravitational test

Friday, March 21st, 2008

Gravity and entanglement

When does a quantum measurement end?

Surprisingly, quantum physicists cannot agree. Some say the measurement ends when you register a result on a piece of classical equipment such as a photomultiplier. Others says the measurement ends when the information in the quantum system has irreversibly leaked into the environment. There are still more who believe in the manyworlds interpretation of quantum mechanics and say a quantum measurement never ends but exists ad infinitum in several parallel universes.

This may sound like an ineffectual academic scrap but it actually has hugely important consequences for the quantum property of entanglement.

Entanglement is the state in which two physically separated particles share the same quantum existence, so that a measurement on one instantaneously affects the other. Yep, that’s instantaneously. It’s what Einstein described as “spooky action at distance”.

For some years, physicists have been measuring this “spooky action at a distance” in tests known as Bell experiments.

These tests depend crucially on the measurement ending quickly. Because if it were to drag on, the particles might be able to communicate at light speed by some currently unknown mechanism.

But because nobody has actually determined when a measurement ends, all the experiments to date are potentially open to this loophole.

Perhaps there is no spooky action at a distance after all, just long quantum measurements during which the particles communicate at the speed of light in some quite ordinary way.

Now Nicolas Gisin and colleagues at the University of Geneva have closed this loophole using the ideas of the Oxford theorist Roger Penrose. A few years ago, he suggested that the end of a quantum measurement is realted to the gravitational energy of the mass distribution of the resulting quantum superposition. In other words, the measurement ends when a massive object receives a decent kick.

So Gisin and buddies set up a Bell experiment which involved sending entangled photons in each direction from the midpoint of an 18 km fibre. At the ends of the fibre were piezoelectric actuators attached to small but massive mirrors. When the photons hit, they triggered the actuators causing the mirrors to move and deflect a beam of light.

The experiment was carefully set up so that the mirrors were heavy enough to please Penrose and far enough apart that no light speed signal could travel between them in the time it took for a pair of entangled photons to “kick” them.

The result? Gisin’s team confirmed that “spooky action at a distance” still governs the behaviour of the entangled photons.

If you believe Penrose, this is the first experiment to ever prove “spooky action at a distance”. Impressive, huh?

More interesting, is the idea of gravity and quantum mechanics coming under the microscope in the same experiment for the first time.

It won’t be the last. There are plenty of other mysteries about gravity that quantum mechanics can probe. It’s about time physicists bit the bullet and started testing them.

Ref: Space-like Separation in a Bell Test assuming Gravitationally Induced Collapses

In case ya missed ‘em…

Sunday, February 24th, 2008

This week’s pearls from the physics arXiv blog:

Saving Earth from the Sun’s expansion

Read it and beep

The quantum graphity question

They came from Mercury…

Ball’s ‘n’ fire

Saturday, February 23rd, 2008

The best of the rest from the arXiv this week:

Plasma Treatment Advantages for Textiles

Electron Mass Shift in Nonthermal Systems

How Efficient is Towing a Cargo by a Micro-swimmer?

Movie Recommendation Systems Using An Artificial Immune System

The hopeless hunt for dark matter

Thursday, October 18th, 2007

Dark matter is highly sought-after but like the unicorn, it is an elusive match for its hunters.

Physics bods have been a-huntin’ for dark matter here on Earth for some time now. They’ve set an impressive number of traps all over the planet and and found zilch.

So they’ve asked the astrobods to help out by looking for indirect evidence. If dark matter particles ever bang into each other, they might annihilate leaving a signature that we can see (or so the thinking goes).

Today, Dan “Super” Hooper from the Fermi National Accelerator in Illinois gives us the low down on the various candidates that the eggheads are looking at.

They’ve looked at the unexplained excess of positrons in cosmic rays, at the unexplained excess of 511KeV photons coming out of the galactic bulge, at the unexplained excess of gamma rays at energies above 1GeV coming from within our galaxy and from outside it and the unexplained excess of microwave emissions from the centre of the Milky Way as measured by the WMAP spacecraft.

None of these signals is particularly strong but that don’t bother dark matter theorists: if it don’t have a current explanation, it’s gotta be dark matter, right?

Whatever happened to that old fashioned notion of hypothesis testing.

I know what ya’ll thinkin and I’ll wager it includes the words “clutching” and “straws”. Myself? I’m rootin’ for the unicorn.

Ref: Indirect Searches For Dark Matter

Friday’s finds

Friday, August 31st, 2007

Today’s highlights from the preprint server

Coherent ultrafast core-hole correlation spectroscopy: x-ray analogues of multidimensional NMR

Secure Transmission with Multiple Antennas: The MISOME Wiretap Channel

Relationship between degree of efficiency and prediction in stock price changes

Tracing the early development of harmful algal blooms with the aid of Lagrangian coherent structures