34.2 General Relativity and Quantum Gravity

This is similar to a phase transition in the universe, and a proposal by American physicist Alan Guth in the early 1980s ties it to the smoothness of the CMBR.

The result of this inflation is that the universe is nearly flat and smooth.

There is no other plausible explanation for the smoothness of the CMBR.

Since any coordination mechanism must travel at the speed of light, the distances between regions of similar temperatures are too great.
Particle physics and cosmology are interdependent.
We can't test the inflationary scenario directly since it occurs at energies much greater than the limits of modern accelerators.
The idea is incorporated into most theories.

The validity of this idea may be determined by the characteristics of the present universe.

The recent indications that the universe's expansion rate may be increasing could mean that we are in another inflationary era.

If conditions found in the early universe could be created in the laboratory, we would see the unification of forces today.

The average energy and separation of particles in the universe have not changed in time.
The four basic forces in nature are not the same under most circumstances.
Evidence from times when the universe was unified can be found in the early universe and its remnants.

When we talk about black holes or unification of forces, we are talking about general relativity and quantum gravity.

The study of how different observers measure the same event, particularly if they move relative to one another, is known as relativity.
Special relativity and classical relativity are used in situations where the speed of light is less than the speed of sound.
Some of the aspects of general relativity that have been verified are better than science fiction.

One needs to understand how all four forces may be unified in order to have a good theory of quantum gravity.

The theory of quantum gravity will encompass all other theories if we are successful.

The case of no observer acceleration was first considered by Einstein when he created the special theory of relativity.

He laid the foundation of general relativity on his own by 1916.
Think about what a person feels in an elevator.
It is the same as being in a stationary elevator.
The person's feet are pressed against the floor and objects fall with the same force.
It is not possible to know what is happening without looking outside.
Einstein believed that gravity and acceleration will produce the same effects.
The beam of light strikes low when the elevator moves up because it seems to the person to bend down.
Einstein said that the same effect must occur because there is no way to tell the effects of gravity on the elevator.
Even though the path of light is massless, gravity affects it.

The beam strikes lower if the elevator is accelerated because the light takes longer to reach the wall.

Einstein's theory of general relativity was verified in 1919 when starlight passed near the Sun during a solar eclipse.

We can briefly see stars during an eclipse.
People in a line of sight close to the Sun should shift their positions.
This shift was observed and it agreed with Einstein's predictions.
The discovery created a sensation.
Einstein was a folk hero as well as a great scientist.
The bending of light by matter is the same as the bending of space itself.
Our concept of space and time has changed a lot.
Any particle with mass or energy is affected by gravity.

There are many current efforts related to general relativity.

The other is the analysis and observation of light.
There is an analysis of the proof of black holes.
The search is on for a direct observation of the waves.
There is a possibility of time travel due to black holes.

The light from a distant galaxy can be "lensed" into several images when it passes by another galaxy on its way to Earth.

Einstein thought it was unlikely that we would ever observe it.
A number of cases of this effect have now been observed, and one is shown in This effect is a much larger scale verification of general relativity.
The red shift is proportional to distance.
Each image of the lensed galaxy has the same red shift as the intervening one.
There is more evidence that red shift is proportional to distance.
If one image varies in brightness over time, the others also vary in the same manner, this is evidence that the multiple images are not different objects.

The Sun is curved toward it in this schematic.

The light that reaches the Earth seems to be coming from different locations.
The amount of bending was exactly what Einstein predicted in his general theory of relativity.

The images of the more distant galaxy are produced by this.

The images have the same spectrum and red shift.
If an object moves straight up from the body, it will be able to escape the gravity of the body.
The escape velocity is determined by the acceleration of gravity on the body.
Light cannot escape if the escape velocity is greater than the speed of light.
Simon Laplace incorporated the idea of a dark star into his writings.
The idea was dropped after Young's experiment showed light to be a wave.
Light could not be acted upon by gravity because it did not have particle characteristics.
After Einstein's theory of general relativity was published in 1916, the idea of a black hole was reborn.

Black holes can form in the collapse of a massive star, forming an object that is 10 km across and has a mass greater than our Sun.

Einstein was one of several physicists who believed nature would find a way to prohibit such objects.

Black holes are difficult to see because they are small.

The event horizon is the edge of the black hole and the radius is the size of a black hole.

Black holes are only a few kilometers larger than the Sun's and are extremely small.
There is an object inside the event horizon.

There is physics near a black hole.

As you approach a black hole, the tidal effects tear matter apart, with matter closer to the hole being pulled in with more force than that only slightly farther away.
This can pull a companion star apart and produce X rays.
X rays from certain star systems are consistent with the picture.
This isn't proof of black holes because the X rays could be caused by something falling onto a star.
The British astrophysicists, Anthony Hewish and Jocelyn Bell, discovered these objects in 1967.
They are formed by the collapse of a star's core in a supernova, in which electrons and protons are forced together to form neutrons.
The black hole of the same mass will not collapse further because of resistance from the strong force.
Nuclear stars cannot have a mass greater than eight solar mass or they will collapse to a black hole.
With recent improvements in our ability to resolve small details, it has become possible to measure the mass of X-ray emitting objects by observing the motion of companion stars and other matter in their vicinity.
There are a lot of X-ray emitting objects that are too large to be stars.
The existence of black holes is widely accepted.
The black holes are close to the centers.

There is evidence that there are black holes at the center of the Milky Way.

A black hole with a mass millions or even billions of times that of the Sun would have formed billions of years ago.
Very distant galaxies are more likely to have energetic cores.
The energy-emitting region must be less than a light year across if Quasar energy outputs vary less than a year.
The best explanation for quasars is that they are young galaxies with a black hole forming at their core, and that they become less energetic over billions of years.
Stars falling into a black hole at the rate of one or more a month is consistent with the amount of energy being emitted from very small regions of space.
An accretion disk in the galaxy M87 was observed by the Hubble Space Telescope.
Further evidence of a black hole as the engine can be found in a jet of material being ejected from the plane of rotation.

A black hole pulls matter away from a companion star, forming a superheated accretion disk where X rays are emitted before the matter disappears forever into the hole.

The two vertical spikes are formed by the in-fall energy.

There are several objects in space that are consistent with the picture and are likely to be black holes.

If a massive object distorts the space around it, like the foot of a water bug on the surface of a pond, then movement of the massive object should create waves in space like those on a pond.

Extreme conditions are needed to generate significant waves of gravity.
The two neutron stars are in close proximity of each other and there is a great amount of gravity near them.
Astronomers Joseph Taylor and Russell Hulse measured the changes in the star system's trajectory.

Direct detection of the waves on Earth would be conclusive.

For a long time, various attempts have been made to detect the waves.
No conclusive events have been observed in this field, which was pioneered by American physicist Joseph Weber.
There are several systems of detectors that are being used around the world.

When gravity is so strong that it has effects on the quantum scale, quantum gravity is important.

Black holes are not the same as the early universe.
The first significant connection between gravity and quantum effects was made in 1971 by the Russian physicist Yakov Zel'dovich.
Black holes can be radiate away energy by quantum effects just outside the event horizon.
Black holes are expected to emit energy and shrink to nothing.
The mechanism is the creation of a pair of particles from energy near the event horizon.
One member of the pair falls into the hole and the other escapes.
When a black hole loses energy and its event horizon shrinks, it creates an even greater gravitational field.
This increases the rate of pair production so that the process grows until the black hole is large.
Smaller black holes are thought to be remnants of the Big bang.

There have been events produced by searches for characteristic -ray bursts.

The Hubble Space Telescope photograph shows the extremely energetic core of the galaxy.

With the superior resolution of the telescope, it has been possible to observe the rotation of an accretion disk around the energy producing object as well as to map jets of material being ejected from the object.
A black hole is consistent with the observations.

Laser interferometer techniques will be used to detect the small vibrations in the detector caused by the gnatational waves.

Direct evidence of gravitational waves would be provided by detection in coincidence with other detectors.
Contributions to the theory of quantum gravity have been made.
The author of popular books on general relativity, cosmology, and quantum gravity is a long-time survivor of the disease.

When a black hole creates a pair of particles from the energy in its field, gravity and quantum mechanics come into play.

One member of the pair falls into the hole while the other escapes and shrinks the black hole.
The characteristic energy is being searched for.