Einstein validated yet again!! Some case studies. (v1.0)

 A pulsar operates akin to a cosmic lighthouse - rotating quickly around its own axis, while emitting a beam of electromagnetic radiation. When observed from Earth, it appears the celestial object periodically emits an electromagnetic "pulse" at consistent intervals. The subsequent "flashes" appear cyclically and consistently enough that a pulsar becomes a useful tool for precise time measurement-- its accuracy rivals that of an atomic clock. This meticulous observation of its behavior was Hulse and Taylor’s Nobel-worthy endeavor. The breakthrough commenced with an observation of PSR B1913+16 - a system comprising a pulsar and a neutron star. Although the name might appear unappealing, its significance for our understanding of the Universe is inestimable.

The pulsar was discovered by Russell Alan Hulse and Joseph Hooton Taylor Jr., of the University of Massachusetts Amherst in 1974. Their discovery of the system and analysis of it earned them the 1993 Nobel Prize in Physics. The crux of Hulse and Taylor's scientific discovery was their measurements, which indicated that the celestial bodies of this system are orbiting faster and faster – with an acceleration of 0.0000765 seconds per year and the system's orbit tightening by roughly 11.5 feet annually. While this might appear insignificant owing to the vast distances inherent in space, it underlines a crucial fact: Einstein was right. The tightening orbit implies that the system is losing energy for some reason. But what's causing this loss? The answer was hinted at by the general theory of relativity: energy "seeps" out of the system in the form of gravitational waves, cast as ripples in space-time. Even though these waves were not directly observed in the '70s, Hulse and Taylor's findings insinuated their existence and subsequently, their measurable impact on our reality, as predicted by Einstein.

It's important to note that the official announcement doesn't always align with the moment of discovery - the results announced in early February 2016 pertained to research conducted six months prior. The instrument used for this research was the American gravitational waves detector, LIGO - twin installations roughly 1865 miles apart, one in Washington and the other in Louisiana. They comprise long (the longer, the better), empty tubes laid out in the shape of an "L". The tube shields a near vacuum through which a laser light beam is projected from the juncture where both tubes meet. The longer the light travels, the higher the chance of observing deviations resulting from the effect of gravitational waves. Although both arms of the detector are precisely the same length, a gravitational wave causes the light to traverse a marginally shorter distance in one of them. "Marginally" is billions of times less than the diameter of an atom nucleus, but large enough to determine that our reality has been skewed: the light took a slightly shorter path because the gravitational wave bent space-time. How long should such a ruler be to indicate the passage of gravitational waves? To enlarge the scale of detected distortions, mirrors are placed in the detectors to reflect the laser dozens or hundreds of times. Thanks to this, for instance, the LIGO detector, whose arms are 2.5 miles long, enables studying the behavior of the light beam over several hundreds of miles. To reduce local disturbance interference, the gathered data is compared with that provided by the European Virgo detector: all detectors should independently register anomalies when gravitational waves pass. However, there's a three-sun mass discrepancy in the total calculation. What became of them? They were dispelled in the form of gravitational waves during the astral collision. These waves hurtled across the cosmos, reaching Earth in 2015, where they interacted with the light transmitted through the detector arms.

Studying gravitational waves can reveal the secrets of the massive, distant objects that released them. Interestingly, by studying the gravitational waves emitted by a pair of slowly colliding binary black holes in 2022, physicists confirmed that the massive objects wobbled — or precessed — in their orbits as they swirled ever closer to one another, just as Einstein predicted they should.

Interestingly, scientists saw Einstein's theory of precession in action yet again after studying a star orbiting a supermassive black hole for 27 years. After completing two full orbits of the black hole, the star's orbit was seen to "dance" forward in a rosette pattern rather than moving in a fixed elliptical orbit. This movement confirmed Einstein's predictions about how an extremely small object should orbit around a comparatively gargantuan one.

Interestingly, Einstein also hypothesized that mass not only warps ("depresses") space-time but also sets it spinning - also called frame dragging - (Lense-Thirring effect), which was corroborated in 2020 in a study of the pulsar PSR J1141-6545. Here is a brief tutorial on the effect: Bing Videos

Lastly As light travels across the universe, its wavelength shifts and stretches in several different ways, known as redshift. The most famous type of redshift is due to the expansion of the universe. (Einstein proposed a number called the cosmological constant to account for this apparent expansion in his other equations). However, Einstein also predicted a type of "gravitational redshift," which occurs when light loses energy on its way out of a depression in space-time created by massive objects, such as galaxies. In 2011, a study of the light from hundreds of thousands of distant galaxies proved that gravitational redshift truly does exist, as Einstein suggested.