Plus Blog

December 11, 2009
Friday, December 11, 2009

In our online poll to find out what Plus readers would most like to know about the Universe you told us that you'd like to find out if time travel is allowed. We took the question to Kip Thorne, Feynmann Professor of Theoretical Physics, Emeritus, at the California Institute of Technology, and here is his answer.



posted by Plus @ 11:05 AM


At 2:00 PM, Blogger Ray said...

I know a little GR; but no Quantum Gravity and very little QM.
I interpret the article as saying that the consensus is: Quantum Gravity can not be fit into Godel's time-closed solution to GR. Is that correct? In that case the global topology would constrain the deeper theories. Put another way Quantum Mechanics can not be embedded/formulated on an arbitrary manifold.
These are questions; not statements.

At 9:25 PM, Blogger Quantum_Flux said...

It is the same thing for observer 1 to rapidly travel into the past as it is for observer 2 to rapidly travel into the future.

At 3:38 PM, Blogger Ray said...

I read references 2,3
3 is quite readable.
2 is tougher and I am not through.
The idea that some local properties can't be extended globally in some topologies is not as strange as it might seem at first glance; there are other examples.
I do have doubts about some of the reasoning; but that doesn't fault the reasoning just the presumptions.
I think its possible that the "energy conditions" are not the right analysis tool. Something along the lines of Entropy (Maxwell's daemon ) might be sharper in the mathematical sense.

At 5:32 PM, Blogger The Grin Reaper said...

Th relation to Casimir vacuums was fascinating. So is the solidarity of Hawking's argument.
Although the possibilities of time travel would lead to the age old grandfather paradox, and I am not sure as to what would be a right explanation. Maybe the Copenhagen interpretation of splitting states to maintain Quantum decoherence.
Cannot say anything conclusively.

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December 11, 2009
Friday, December 11, 2009

Professor risk

Are you a committed non-smoker who loves rock climbing? Then, like most of us, your have an ambivalent attitude to risk. Some risks are so much fun they're worth taking, and others you definitely stay clear of. But what's the attitude of a risk professional like David Spiegelhalter, Cambridge Professor of Public Understanding of Risk (and regular contributor to Plus)? Find out in this short video posted on the Cambridge Ideas website.

posted by Plus @ 3:41 PM


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December 3, 2009
Thursday, December 03, 2009

Infectious diseases hardly ever disappear from the headlines. If it's not the disease itself that hits the news, then it's the vaccines with their potential side effects. It can be hard to tell the difference between scare mongering and responsible reporting, because media coverage rarely provides a look behind the scenes. How do scientists reach the conclusions they do? How do they predict how a particular disease will spread, and whether it is likely to mutate into a more dangerous strand? And how do they assess the impact of an intervention like vaccination, and make sure that a vaccine is safe?

Two answer these questions, we have put together a package of five articles, a podcast, and a classroom activity.


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posted by Plus @ 12:50 PM


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December 3, 2009
Thursday, December 03, 2009

Vaccination is an emotive business. The furore around the MMR vaccine and autism has shown that vaccination health scares can cause considerable damage: stop vaccinating, and epidemics are sure to follow. But how do scientists decide whether a vaccine and a vaccination strategy are effective and safe? We talk to Paddy Farrington, Professor of Statistics at the Open University. You can also read the accompanying article.

Listen to the podcast.

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posted by Plus @ 12:43 PM


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November 25, 2009
Wednesday, November 25, 2009

An amateur fractal programmer has discovered a new 3D version of the Mandelbrot set. Daniel White's new creation is based on similar mathematics as the original 2D Mandelbrot set, but its infinite intricacy extends into all three dimensions, revealing fractal worlds of amazing complexity and beauty at every level of magnification.



posted by Plus @ 9:45 AM


At 12:56 PM, Anonymous Anonymous said...

I want this as screensaver,awesome

At 2:27 PM, Blogger David Makin said...

Those interested in more about the Mandelbulb and the search for the "true 3D" Mandelbrot including an almost complete history of the last couple of years search may wish to look here

At 10:30 AM, Blogger miner49er said...

What's the explanation for the fracvtal nature of the mandelbrot set? Is it an anomoly in the number system? Is it basically an error?

I have been fascinated by fractals for 20 years but never really thought about _why_ they (mandelbrot/escape-time) exist.

I wonder if discovering why they exist at all, may lead to a 'better' 3D analog?

At 7:06 AM, Blogger Djeimz said...

Interesting article. Interesting pictures.

However, I'm wondering if there isn't a typo in the formula given. If it is a direct generalization of complex multiplication using Euler angles, the z-component should be:
-sin(n phi)
and not:
-sin(n theta)
Am I wrong?


At 10:25 AM, Anonymous The Plus Team said...

Thanks Djeimz, you're right and it's been corrected!

At 12:12 AM, Blogger Paolo Bonzini said...

It is possible to describe this fractal also using quaternions. This is interesting in that it removes the need to define a special, non-standard exponentiation function.

See [PDF] (thanks to the people on and for proofreading!)

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November 19, 2009
Thursday, November 19, 2009

LHC set for restart

After over a year of repair works the Large Hadron Collider at CERN may be restarted within the next few days. Scientists will gently prod the giant particle collider back into action, starting by circulating beams of protons at low energies and generating low energy collisions, before slowly firing it up to its full power. It is hoped that eventually the high energy collisions will generate conditions similar to those right after the Big Bang and shed light on some of the biggest mysteries of the Universe.

To remind yourself of what the LHC is all about, read the Plus articles:

Or, for a quick fix, here's the LHC rap:

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