<< Chapter < Page Chapter >> Page >

Quantum gravity

Black holes radiate

Quantum gravity is important in those situations where gravity is so extremely strong that it has effects on the quantum scale, where the other forces are ordinarily much stronger. The early universe was such a place, but black holes are another. The first significant connection between gravity and quantum effects was made by the Russian physicist Yakov Zel’dovich in 1971, and other significant advances followed from the British physicist Stephen Hawking. (See [link] .) These two showed that black holes could radiate away energy by quantum effects just outside the event horizon (nothing can escape from inside the event horizon). Black holes are, thus, expected to radiate energy and shrink to nothing, although extremely slowly for most black holes. The mechanism is the creation of a particle-antiparticle pair from energy in the extremely strong gravitational field near the event horizon. One member of the pair falls into the hole and the other escapes, conserving momentum. (See [link] .) When a black hole loses energy and, hence, rest mass, its event horizon shrinks, creating an even greater gravitational field. This increases the rate of pair production so that the process grows exponentially until the black hole is nuclear in size. A final burst of particles and γ size 12{γ} {} rays ensues. This is an extremely slow process for black holes about the mass of the Sun (produced by supernovas) or larger ones (like those thought to be at galactic centers), taking on the order of 10 67 size 12{"10" rSup { size 8{"67"} } } {} years or longer! Smaller black holes would evaporate faster, but they are only speculated to exist as remnants of the Big Bang. Searches for characteristic γ size 12{γ} {} -ray bursts have produced events attributable to more mundane objects like neutron stars accreting matter.

The image on the left shows what appears to be a spherical white burst of dust from which two yellow-orange jets emanate, one going up and the other going down. From the top of the upper jet to the bottom of the lower jet is about one hundred and eighty thousand light years. The background is black. The center of the white burst is expanded in the image on the right and appears as a bright yellow doughnut-shaped disk spread over four hundred light years. At the center of the disk is a bright spot that may be the source of the jets.
This Hubble Space Telescope photograph shows the extremely energetic core of the NGC 4261 galaxy. With the superior resolution of the orbiting 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 supermassive black hole is consistent with these observations, but other possibilities are not quite eliminated. (credit: NASA and ESA)
This figure shows a windowless room full of desks and computer screens and with three large screens on the wall upon which are projected a lot of technical graphs.
The control room of the LIGO gravitational wave detector. Gravitational waves will cause extremely small vibrations in a mass in this detector, which will be detected by laser interferometer techniques. Such detection in coincidence with other detectors and with astronomical events, such as supernovas, would provide direct evidence of gravitational waves. (credit: Tobin Fricke)
A photo of Stephen Hawking sitting on his special chair fitted with modern gadgets.
Stephen Hawking (b. 1942) has made many contributions to the theory of quantum gravity. Hawking is a long-time survivor of ALS and has produced popular books on general relativity, cosmology, and quantum gravity. (credit: Lwp Kommunikáció)
The figure shows a purple doughnut-shaped object with a black hole in the middle. Many different-colored spots are arranged like glazing around the edge of the doughnut. The deep purple of the doughnut fades to a light purple as you move away from the doughnut, and the space around the doughnut is filled with randomly placed white dots. Various particles are shown either falling in or escaping from the doughnut. There is a proton antiproton pair, with the proton escaping and the antiproton falling back into the doughnut. There is an electron-positron pair in which the positron escapes then annihilates with an electron outside the doughnut, with the subsequent gamma rays escaping the doughnut. There is a muon-antimuon pair that is created then both fall back into the doughnut. Finally, there is an electron-positron pair that is generated, with the electron escaping and the positron falling back into the doughnut.
Gravity and quantum mechanics come into play when a black hole creates a particle-antiparticle pair from the energy in its gravitational field. One member of the pair falls into the hole while the other escapes, removing energy and shrinking the black hole. The search is on for the characteristic energy.

Questions & Answers

what is fluid
Anthony Reply
anything that flows is Liquid.
a substance that has no specific shape
How submarines floats one water the same time sink in water
Courage Reply
A submarine has the ability to float and sink. The ability to control buoyancy comes from the submarine'strim or ballast tanks which can be filled with either water or air, depending on whether the submarine needs to floator sink. When the submarine floats it means its trim tanks are filled with air
what is work
Ojo Reply
Force times distance
product of force and distance...
Is physics a natural science?
Adebisi Reply
what is the difference between a jet engine and a rocket engine.
Samuel Reply
explain the relationship between momentum and force
Joseph Reply
A moment is equivalent multiplied by the length passing through the point of reaction and that is perpendicular to the force
How to find Squirrel frontal area from it's surface area?
Pooja Reply
how do we arrange the electronic configuration of elements
Muhammed Reply
hi guys i am an elementary student
benedict Reply
are you an elementary student too?
no bro
what is the four equation of motion
what is strain?
Change in dimension per unit dimension is called strain. Ex - Change in length per unit length l/L.
strain is the ratio of extension to length..=e/l...it has no unit because both are in meters and they cancel each other
How is it possible for one to drink a cold drink from a straw?
Karanja Reply
most possible as it is for you to drink your wine from your straw
state the law of conservation of energy
Sushma Reply
energy can neither be destroy or created,but can be change from one form to another
it can neither be created nor destroyed
its so sample question dude
what is the difference between a principle and a law?
Mary Reply
where are from you wendy .?
you are beautiful
are you physics student
laws are ment to be broken
hehe ghulam where r u from?
principle are meant to be followed
south Africa
here Nigeria
principle is a rule or law of nature, or the basic idea on how the laws of nature are applied.
Rules are meant to be broken while principals to be followed
principle is a rule or law of nature, or the basic idea on how the laws of nature are applied.
what is momentum?
prakash Reply
is the mass times velocity of an object
it is the product of mass and velocity of an object.
The momentum possessed by a body is generally defined as the product of its mass and velocity m×v
momentum is the product of the mass of a body of its velocity
what about kg it is changing or not
vijay Reply
no mass is the quantity or amount of body so it remains constant everywhere
remains constant
mass of an object is always constant. and that is universally applied.
mass of a body never changes but the weight can change due to variance of gravity at different points of the world
what is hookes law
mass of an object does not change
Is weight a scalar quantity
esther Reply
weight is actually a force of gravity with which earth attracts us downwards so it is a vector quantity. and it has both direction and magnitude
weight is the earth pull of the body
why does weight change but not mass?
Theo, the mass of an object can change but it depends on how you define that object. First, you need to know that mass is the amount of matter an object has, and weight is mass*gravity (the "force" that attracts object A to the object B mass).
So if you face object A with object B, you will get a different result than facing object A with object C, so the weight of object A changes but not its mass.
Now, if you have an object and you take a part away from it, you are changing it mass. Lets use the human body and fat loss process as an example.
When you lose weight by doing exercise, you are being attracted by the same object before and after losing weight so the change of weight is related to a change of mass not a change of gravity.
The explanation of this is simple, we are composed of smaller particles, which are itself objects, so the loose of mass of an object actually is the separation of one object is two different ones.
But if you define an object because of its form and characteristics and not the amount of mass, then the object is the same but you have taken a part of it mass away.
Theo, weight =mass. gravity, here mass is fixed everywhere but gravity change in different places so weight change not mass.
yup weight changes and mass does not. That's why we're 1/3 our weight on the moon
weight is the product of mass × velocity w=m×v = m(v-u) but v=u+1/2at^ weight is a scalar quantity mass of an obj is the amount of particles that obj cont
mass is fixed always while weight is dynamic
Why does water wet glass but mercury does not?
thanks guys
Yusuf Shuaibu, for water the Adhessive force between water molecules and glass is greater than the cohessive force between it's own molecules but for Mercury the cohessive force will be greater in comparison with adhessive force. For this water wet glass but Mercury does not.

Get the best College physics course in your pocket!

Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?