Particle physics

Physicists Propose a Mirror Universe Where Time Moves in the Opposite Direction

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Imagine waking up after death and living out your old age, until you grew young enough to have a career, and hoped someday to go to college. This is what life might be like in the “mirror” universe, the exact opposite of ours. According to two teams of physicists, our universe may have a twin where time moves backward.

Of course, this is all just theoretical. But the theory answers some fundamental questions physics has been wrestling with for quite some time. One is, if the universe during the Big Bang was made of equal parts matter and antimatter, where’s all the antimatter?

Paul Dirac first proposed antimatter in 1928. Since then, physicists have found a wide range of antiparticles. These are present during high energy collisions in other places in the universe and also within particle accelerators, such as the large hadron collider at CERN.

In a 1964 experiment, which won them the Nobel Prize 16 years later, James Cronin and Val Fitch proved that you cannot have an antimatter universe for the simple reason that the weak nuclear force violates this model. For a while that was that.

Then in 2004, two scientists at Caltech, Professor Sean Carroll and his graduate student Jennifer Chen, revived the mirror universe theory, by trying to address another fundamental physics question, why does time only move in one direction?

Experiments at the HLC at CERN have shown antimatter. But it’s eerily absent in nature. Getty Images.

Through the course of their investigation, they ended up creating a model of the Big Bang which shoots outward in two opposite directions. In our universe, everything is made up of matter, while in the mirror universe, its antimatter.

As time moves forward in one direction in one universe, it moves backward in the other. But from the mirror universe, time would appear to be moving backwards in ours, which begs the question, who is actually in the backwards universe, us or them?

Generally speaking, when we talk about time, we consider the Second Law of Thermodynamics and in particular, entropy. This is the amount of disorder in a system which will eventually break it down, be it an engine,…

Lawrence Krauss – Lux Ex Machina – Think Again Podcast #98

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Physicist Lawrence Krauss directs the Origins Project at Arizona State University, which fosters scientific research and collaborations on origins – of life, the universe, and everything. His own research focuses on the interface between elementary particle physics and cosmology, including investigations into dark matter and the origin of all mass in the universe. His latest book The Greatest Story Ever Told – So Far is a deeply entertaining and informative account of the progress of knowledge in modern physics.


Collider data hint at unexpected new subatomic particles

LHCb experiment
WEIRD DECAYS Something funny may be going on in certain particle decays measured in the LHCb experiment in Geneva (above). A new measurement has now added to scientists’ suspicions.

A handful of measurements of decaying particles has seemed slightly off-kilter for years, intriguing physicists. Now a new decay measurement at the Large Hadron Collider in Geneva has amplified that interest into tentative enthusiasm, with theoretical physicists proposing that weird new particles could explain the results. Scientists with the LHCb experiment reported the new result on April 18 in a seminar at the European particle physics lab CERN, which hosts the LHC.

“It’s incredibly exciting,” says theoretical physicist Benjamin Grinstein of the University of California, San Diego. The new measurement is “a further hint that there’s something new and unexpected happening in very fundamental interactions.”

Other physicists, however, are more cautious, betting that the series of hints will not lead to a new discovery. “One should always remain suspicious of an effect that does not show up in a clear way” in any individual measurement, Carlos Wagner of the University of Chicago wrote in an e-mail.

Taken in isolation, none of the measurements rise beyond the level that can be explained by a statistical fluctuation, meaning that the discrepancies could easily disappear with more data. But, says theoretical physicist David London of the University of Montreal, there are multiple independent hints, “and they all seem to be pointing at something.”

The measurements all involve a class of particle called a B meson, which can be produced when protons are smashed together in the LHC. When a B meson decays, it can produce a type of particle called a kaon that is accompanied either by…

Rare triplet of high-energy neutrinos detected from an unknown source

IceCube Neutrino Laboratory
THRICE AS NICE Using detectors buried in the Antarctic ice, the IceCube Neutrino Observatory detected a rare burst of three neutrinos.

Three high-energy neutrinos have been spotted traveling in tandem.

The IceCube Neutrino Observatory in Antarctica detected the trio of lilliputian particles on February 17, 2016. This is the first time the experiment has seen a triplet of neutrinos that all seemed to come from the same place in the sky and within 100 seconds of one another. Researchers report…