Home News Time reversibility might be the reason why gamma-rays seem to travel backward

Time reversibility might be the reason why gamma-rays seem to travel backward

Time reversibility might be the reason why gamma-rays seem to travel backward
(Credit: DESY, Science Communication Lab)

It is known that time can move in only one direction. However, last year scientists detected some events in which the gamma-ray bursts seemed to repeat as if they were moving backward in time. 

New research suggests the potential answer to the cause of this time reversibility effect. If the waves in the relativistic jets producing gamma-ray bursts propagate faster than light at what is known as “superluminal speeds”, then one of its possible effects could be time reversibility. The work appears in The Astrophysical Journal. 

When light travels through a medium, the phase velocity is lesser than the light’s speed in a vacuum, which is the ultimate speed barrier in the Universe. Hence a wave could move through gamma-ray burst jet at superluminal speeds without violating relativity. The most energetic explosions in the Universe are gamma-ray bursts. While they can last a time span ranging milliseconds to hours, they are very bright and till now no concrete reason for their cause is found.

From 2017 observations of colliding neutron stars, it is known that gamma-ray bursts can be created from these collisions. When a huge, violently spinning star collapses to black hole resulting in the ejection of material in a colossal hypernova then these bursts can be produced. Then the black hole is surrounded by the accretion material around the equator. With quick rotation, the exploded material falls back resulting in relativistic jets from the polar regions. It blasts through the outer envelope of the star resulting in gamma-ray bursts. 

Particles can move faster than light when traveling through a medium. This causes Cherenkov radiation which is viewed as a blue glow, also known as a luminal boom. When particles such as electrons travel faster than the phase velocity of light in the medium then the glow is produced. 

Scientists Jon Hakkila, College of Charleston and Robert Nemiroff, Michigan Technological University think that the same effect is responsible for gamma-ray burst jets. They have created mathematical modeling to demonstrate it. They mention in their model that an impactor wave in a gamma-ray burst either propagates from subluminal to superluminal velocities or decelerates vice-versa. This impactor wave interacts with the medium resulting in Cherenkov radiation when moving faster than light’s speed in the medium or creates a synchrotron shock radiation when moving slower than the light’s speed. 

A time-forward and time-reversed set of light curve features are created by the transitions by relativistic image doubling. When a charged particle enters the water near to light’s speed, it moves faster than Cherenkov radiation resulting in the illusion of appearing at two places simultaneously, one seems to travel ahead in time and one backward. 

This has not yet been observed experimentally. If verified it might be responsible for the time-reversibility in gamma-ray burst light curves. 

Researchers made an assumption that impactor creating gamma-ray burst would be a wave of a large scale produced by changes of the magnetic field. More analysis is needed in this direction. Since the model includes time-reversibility it explains gamma-ray bursts much better than those which don’t. 

Reference: The Astrophysical Journal.


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