General relativity explained

General relativity is physicist Albert Einstein's understanding of how gravity affects the structure of space-time. This theory published by Einstein in 1915 extends the special theory of relativity he published 10 years ago. The special theory of relativity believes that space and time are inseparable, but the theory does not recognize the existence of gravity.


According to NASA, in the ten years between the two publications, Einstein determined that extremely large objects distorted the structure of space-time. This distortion is manifested in gravity.

How does general relativity work?

To understand general relativity, first, let's start with gravity, the force of attraction that two objects exert on one another. Sir Isaac Newton quantified gravity in the same text in which he formulated his three laws of motion, the "Principia."

The gravitational force between two objects depends on the mass of each object and the distance between the two objects. Even if the centre of the earth pulls you toward it (to keep you firmly on the ground), your centre of gravity will be pulled back to the earth. But a bigger body can hardly feel your pull, your mass is much smaller, and you will find yourself firmly rooted with the same strength. However, Newton's law assumes that gravity is the innate force of an object.

Albert Einstein determined in his special theory of relativity that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light in a vacuum is the same no matter what speed the observer travels.

As a result, he discovered that space and time are intertwined into a single continuum called space-time. Events that occur at the same time for one observer may occur at different times for another observer.

When Einstein calculated the equations for his general theory of relativity, he realized that huge objects would cause space-time distortions. Imagine placing a large object in the centre of the trampoline. The object will press down into the fabric, causing it to dent. Then, if you try to roll the marbles on the edge of the trampoline, the marbles will spin inward toward your body in a way that is very similar to the way planetary gravity pulls rocks in space.

In the decades since Einstein published his theory, scientists have observed countless phenomena consistent with the predictions of the theory of relativity.

Gravitational lensing

Light bends around a huge object, such as a black hole, making it a lens of the object behind it. Astronomers often use this method to study the stars and galaxies behind massive objects. According to the European Space Agency (ESA), Einstein’s Cross is a quasar in the constellation Pegasus and is a good example of gravitational lensing. The quasar is thought to be about 11 billion years ago; the galaxy in which it is located is about 10 times away from Earth.

In a situation like Einstein's cross, different images of the gravitationally lensed object will appear at the same time, but this is not always the case. The scientists also managed to observe the example of the lens, because the light propagating around the lens takes different paths of different lengths, and different images arrive at different times, such as a particularly interesting supernova.

Changes in Mercury's orbit

According to NASA, the orbit of Mercury will gradually change over time due to the curvature of space-time around the massive sun. After billions of years, this swing may even cause the innermost planet to collide with the sun or planets.

Frame dragging of space-time around rotating bodies

The rotation of a heavy object (such as the earth) should distort and distort the space-time around it. In 2004, NASA launched the Gravity Probe B (GP-B). According to NASA, the axis of the satellite's precisely calibrated gyroscope drifts very slightly over time. This result is consistent with Einstein's theory.

As the planet rotates, the honey around it rotates, and so does space and time. GP-B confirmed the two most profound predictions of Einstein's universe and had a profound impact on astrophysics research.

The electromagnetic radiation of the object stretches slightly in the gravitational field. Think of the sound waves emitted from the siren on an emergency vehicle; when the vehicle moves toward the observer, the sound waves are compressed, but when it moves away, they are stretched or redshifted. Known as the Doppler effect, the same phenomenon occurs in light waves of all frequencies.

According to the American Physical Society, in the 1960s, physicists Robert Pound and Glenn Rebka first shot gamma rays down and then shot them up to the towers of Harvard University. Pound and Rebka discovered that the frequency of gamma rays changes slightly due to the distortion caused by gravity.

Gravitational waves

Einstein predicted that violent events, such as the collision of two black holes, would produce ripples in space and time called gravitational waves. In 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the first detection of such a signal.

The test took place on September 14, 2015. LIGO is composed of dual facilities located in Louisiana and Washington state, which have recently been upgraded and calibrated before going live. According to the LIGO spokesperson at the time, Gabriela Gonzalez (Gabriela Gonzalez), the first detection was so large that it took the team months of analysis to convince itself that it was a real signal. , Not malfunction.

Since then, scientists have begun to quickly capture gravitational waves. According to project officials, in total, LIGO and its European counterpart Virgo have detected 50 gravitational wave events.

These collisions include unusual events, such as collisions with objects that scientists cannot clearly identify as black holes or neutron stars, merging neutron stars with bright explosions, collisions with mismatched black holes, and so on.

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