Knowing Black Hole

Source: The Hitavada      Date: 08 Jan 2019 12:24:38


‘Hawking’s radiation’ was proposed by the great Stephen Hawking. Before I start, again you’ll need to understand some very important stuff. A black hole is that region in space which is so dense and has that enormous gravitational force that even light can't escape through it. Remember, I told you last weak, how huge the speed of light that it stays the fastest. Heisenberg’s uncertainty principle says that two conjugate variables, such as position and momentum along the same axis cannot both have arbitrarily precise values. The product of the uncertainties in the two variables must be greater than Planck’s constant .
But for this context, we'll be using different interpretation of 'Uncertainty principle'which gives rise to virtual particles .The equation for the uncertainty principle is. This equation allows small, momentary deviation from perfect energy conservation (I guess, I’ve already informed you that). It means if one measures time associated with a physical process threreby reducing the uncertainty in time, there is a corresponding increase in the uncertainty of energy associated with the same physical process and vice versa.

The rules of quantum mechanics say that this principle applies not only to particles but to everything in the universe-even to a region of space. But doesn’t empty space have zero energy? No, according to the uncertainty principle. If empty space had zero energy, then we would have precise information about dE which violates the uncertainty principle because energy and time are complementary and if we have precise information about energy, we can’t have precise information about dT, that is to say how long that region of space carries that energy. More over the equation has to to be satisfied. If the region has energy rE=0, then the left side of the equation reduces to 0 due to the product relation between rE and rT.

This means both, the energy rE and time duration rT are 0, whereas according to the equation, both these values are complementary. If one becomes larger, the other becomes smaller and vice versa, but can't be exactly same. Thus even empty space does have non zero energy. But how can empty space have energy if there is nothing to carry it? Nature takes care of us for that.

Virtual particle-anti-particle pairs are created all the time within the quantum foam, which makes up the vacuum of space. The total energy of the pair is zero (since the energy of the vacuum was zero to begin with). This means that the energy of one of the particles of the pair must be negative. Negative energy particles cannot exist (except as quantum fluctuations, for the briefest moment in time, in accordance with the energy-time uncertainty principle) so the pair quickly annihilates, and nothing is left… Nothing before = nothing after.

Having this fundamental understanding about the quantum theory and virtual particles, let's now understand what is Hawking's radiation. As said earlier, enough energy can be 'borrowed' accoding to Heisenberg to allow spontaneous creation of particle-anti particle pair any time any where. Using this result,Stephen Hawking said that black holes evaporate via Hawking radiation: Whenever these virtual parties come into existence , they come in a pair of positive and negative energy , for example - 2 anti particle , one with positive and other with negative energy. This accounts for the neutral nature of the universe. We know, when an object is in a gravitational field, then the amount of energy it has, is negative and becomes more negative as we take it more closer to the object, which has created the gravitational field as in this case a black hole.

Here when the particles come into existence, one which is having negative energy falls into the black hole. In turn, the positive energy member of the pair (which may be a normal particle or an antiparticle) becomes real since it has lost its virtual twinand can have enough energy ( enough amount of binding energy to escape the black holes gravitational pull ) to leave the vicinity of the black hole altogether. In this case the total mass of the black hole is reduced because it consumed something with negative energy.



Akruti Mishra
Class XII, Shivaji Science College