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pierredv : gravity   8

Exclusive: Grave doubts over LIGO's discovery of gravitational waves | New Scientist Nov 2018
“We believe that LIGO has failed to make a convincing case for the detection of any gravitational wave event,” says Andrew Jackson, the group’s spokesperson. According to them, the breakthrough was nothing of the sort: it was all an illusion.
LIGO  gravity  cosmology  experiment  NewScientist  physics 
april 2019 by pierredv
The geometry that could reveal the true nature of space-time | New Scientist issue 3136, 29 Jul 2017
"The discovery of an exquisite geometric structure is forcing a radical rethink of reality, and could clear the way to a quantum theory of gravity"

[Andrew Hodges, one of Penrose’s colleagues at Oxford] "showed that the various terms used in the BCFW method could be interpreted as the volumes of tetrahedrons in twistor space, and that summing them up led to the volume of a polyhedron."

"So why invoke virtual particles at all? ... The first is that dealing with them rather than with fields makes the maths more tractable. The other great advantage is that they help physicists visualise everything as the well-defined interactions between point-like particles, as opposed to the hazy goings-on between particles and fields. This fits nicely with the intuitive principle of locality, which holds that only things in the same spot in space and time can interact. Finally, the technique also helps enforce the principle of unitarity, which says that the probability of all outcomes should add up to 1."

Gluon interactions seemed to complex, but "In 1986, Stephen Parke and Tomasz Taylor from Fermilab near Batavia, Illinois, used Feynman diagrams and supercomputers to calculate the likelihoods of different outcomes for interactions involving a total of six gluons. A few months later, they made an educated guess at a one-line formula to calculate the same thing. It was spot on. More than 200 Feynman diagrams and many pages of algebra had been reduced to one equation, and the researchers had no idea why."

"In 2005, Ruth Britto, Freddy Cachazo, Bo Feng and Edward Witten [BCFW] were able to calculate scattering amplitudes without recourse to a single virtual particle and derived the equation Parke and Taylor had intuited for that six-gluon interaction"

[Nima Arkani-Hamed and his team at IAS] "arrived at a mind-boggling conclusion: the scattering amplitude calculated with the BCFW technique corresponds beautifully to the volume of a new mathematical object. They gave a name to this multi-dimensional concatenation of polyhedrons: the amplituhedron."

"It may transform physics, too ... because the amplituhedron does not embody unitarity and locality, those core principles baked into reality as described by Feynman diagrams. ... If so, locality is not a fundamental feature of space-time but an emergent one."
NewScientist  geometry  physics  gravity  field-theory  quantum-mechanics  twistors  Roger-Penrose  Richard-Feynman  Ed-Witten  maths 
december 2017 by pierredv
Einstein's silence: Listening for space-time ripples - physics-math - 13 April 2014 - New Scientist
The stories/factoids about all the noise they have to compensate for reminded me of a meditation sit. The sensitivity is amazing: "When we were running, we saw storms in the North Sea." Also: "Mysterious, irregular, Doppler-shifted acoustic noise at LIGO-Hanford coincided with arrival and departure times at Richland airport some 20 kilometres away. Then there were the times every few nights in spring when a mysterious noise would roll to a sudden crescendo and ebb away slowly – the rumble of rushing meltwater released from nearby dams."
gravity  LIGO  silence  meditation  noise  measurement  NewScientist 
may 2014 by pierredv
The surprise theory of everything -Vlatko Vedral -October 2012 -
"The question is whether we can express the whole of physics simply by enumerating possible and impossible processes in a given situation. This is very different from how physics is usually phrased, in both the classical and quantum regimes, in terms of states of systems and equations that describe how those states change in time. . . ." "Apply this logic more generally, and time ceases to exist as an independent, fundamental entity, but one whose flow is determined purely in terms of allowed and disallowed processes. With it go problems such as that I alluded to earlier, of why the universe started in a state of low entropy. If states and their dynamical evolution over time cease to be the question, then anything that does not break any transformational rules becomes a valid answer."
*  NewScientist  science  thermodynamics  physics  gravity 
november 2012 by pierredv

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