Wednesday, March 07, 2007

New Ideas Take Over

This is the sleek interior of the new 747-8. It will use the fuel-saving technology of the 787 to achieve a lower cost per seat-mile than any competitor, especially the A-380. Lufthansa has already ordered 20 of the passenger version, with options for 20 more. For 747 pilots, the new version requires almost no re-qualification. Though the 747 design is decades old, it is still prettier than the A-380. Starting in 2010, we can fly across oceans in this!

Airbus is in big, big trouble. The A-380 was launched with huge fanfare. Building the world's biggest airliner was seen as the next big thing. Now the project is in such expensive trouble that it may sink Airbus. The freighter version for Fedex and UPS has been completely cancelled. The distraction has delayed Airbus from developing a competitor to the very popular 787. The bigger they are, the harder they fall.

Steinn from Dynamics of Cats is the latest to wonder about "Lorentz Invariance," or a changing speed of light. Last month Roger Blandford wondered about c change too. Steinn started his career in strings, got sick of that and has since made many entertaining blog posts. Welcome to the club!

The most convincing evidence, as Mahndisa and Roger Blandford have alluded to, may be Ultra-High Energy Cosmic Rays. The "Oh My God" particles have energies far higher than expected. They are difficult to explain with a fixed speed of light. Along with supernova evidence, massive primordial Black Holes, supernovae and the "Faint Young Sun" the evidence is mounting.

The "standard cosmological model" has been called the Concorde cosmology like a plane which no longer flies. It is likely to linger around gathering dust for a long time. Some old folks will go to their grave muttering that the speed of light is constant. Gathering evidence for a "c change" takes years. As more and more supporting data appears, a better model will take over.

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Blogger nige said...

"Steinn from Dynamics of Cats is the latest to wonder about "Lorentz Invariance," or a changing speed of light."

Thanks for this link. Smolin does explain why the Lorentz invariance breaks down at say the Planck scale in his book "Trouble with Physics".

Simply put, the vacuum is composed of particles with some size like the Planck scale, which is independent of Lorentz contraction.

Hence, special relativity must break down for very small scales.

Doubly special relativity is any scheme whereby you retain speciality for large distance scales, but lose it for small ones.

Doubly special relativity was applied by Giovanni Amelino-Camelia in 2001 to explain why some cosmic rays have been detected with energies exceeding the limit of special relativity, 5 x 10^19 eV = 3 J (the Greisen-Zatsepin-Kuzmin limit). It's not just LQG which makes a speculative prediction, because there's experimental evidence validating it!

Actually, there are quite a lot of indications of this non-Lorentzian behaviour in quantum field theory, even at lower energies, where space does not look quite the same to all observers due to pair production phenomena. For example, on page 85 of their online Introductory Lectures on Quantum Field Theory, Professors Luis Alvarez-Gaume and Miguel A. Vazquez-Mozo explain, hep-th/0510040:

‘In Quantum Field Theory in Minkowski space-time the vacuum state is invariant under the Poincare group and this, together with the covariance of the theory under Lorentz transformations, implies that all inertial observers agree on the number of particles contained in a quantum state. The breaking of such invariance, as happened in the case of coupling to a time-varying source analyzed above, implies that it is not possible anymore to define a state which would be recognized as the vacuum by all observers.

‘This is precisely the situation when fields are quantized on curved backgrounds. In particular, if the background is time-dependent (as it happens in a cosmological setup or for a collapsing star) different observers will identify different vacuum states. As a consequence what one observer call the vacuum will be full of particles for a different observer. This is precisely what is behind the phenomenon of Hawking radiation.’

Sadly, some string theorists are just unable to face the facts and understand them:

‘... the rules of the so-called "doubly special relativity" (DSR) to transform the energy-momentum vectors are nothing else than the ordinary rules of special relativity translated to awkward variables that parameterize the energy and the momentum.’ -

‘... Still, I just want to say again: DSR and Lorentz violation just aren't in any way predictions of LQG.’ - Aaron Bergman,

LQG does quantize spacetime. Smolin makes the point clearly in "The Trouble with Physics" that whatever the spin network grain size in LQG, the grains will have an absolute size scale (such as Planck scale, or whatever).

This fixed grain size contradicts the Lorentz invariance, and so you have to modify special relativity to make it compatible with LQG. Hence, DSR in some form (there are several ways of predicting Lorentz violation at small scales while preserving SR at large scales) is a general prediction of LQG.

12:09 AM  
Blogger nige said...

Sorry one sentence in my comment above should read:

Doubly special relativity is any scheme whereby you retain special relativity for large distance scales, but lose it for small ones.

I'm typing too fast.

12:14 AM  
Anonymous a quantum diaries survivor said...

Wow Louise,
how many great posts to read, back from vacation! Thank you for the news on the new lufthansa fleet, I will be using it soon... The new design of the 747 does look great, I hope they redesigned the seats too (and _not_ to make them even less spacious!).
Another hope is that they will go back to providing wireless internet on board. What a shame Connexions withdrew...


3:52 PM  
Blogger Kea said...

Gorgeous decor, but the blue lighting probably isn't the best thing for the faces of people on 13+ hour flights. I can't wait to take a flight on one of these!

2:12 PM  
Blogger L. Riofrio said...

Welcome back, T. I hope the family enjoyed Cancun. I would love to be flying Lufthansa to Europe this month. Your comments in various publications are very exciting.

Kea, after many flights across the Pacific I am happy for anything that makes the trip faster, more comfortable or more fuel-efficient.

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