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James

Hi, buddies, do you remember Stephen Hawking visited Hong Kong last year.  He is one of the greatest minds and undoubtedly the most famous scientists in modern time.  But why is he so famous?   Stephen Hawking is famous because he describes the cosmos in laymen terms in his bestselling book "A Brief History of Time".  He popularizes theoretical physics so that everyone with some imagination and high school education is able to contemplate about the origin of the universe, the beginning of time,  black holes,  and the role of women in the cosmos.  I am sure you have read the book.   No? Well, even if you don't like science - which I can tell, there are two books you must have.  The first book is "A Brief History of Time"  and the second one is "Men are from Mars, Women are from Venus".   Now, don get any wrong idea.  I respect woman as much as I respect people with different religious belief and skin colour.

Back to our topic.  We ordinary people think that Stephen Hawking is great because he is the only scientist that openly admits he doesn't understand women.  But to physicists Stephen Hawking is great because he is the person  that discovers that black hole is not really black after all.  Now, don't tell me that you don't know what black hole is.  Well, you do know, right?   But you want me to explain in my own words.  Ok, I'll do it.  But of course I am not as good as Professor Hawking in explaining advanced knowledge to laymen.  So forgive me if I can't make myself fully understood. 

You see, light has the strange temperament of sometimes behaving like .....light, and sometimes behaving not so much like light.   Reminds you of your computer, right?  When it doesn't behave like light, it acts  like particles with mass.  And with mass it must be attracted to gravity.  Black holes  are the heaviest and densest objects in the known universe.  So heavy that its gravity will pull light and all other kinds of electromagnetic radiation near its vicinity into the black hole.  Hence it is black because no lights will ever come out of it.    And if something as light as light cannot escape, what else can?  So for quite  a long time scientists were quite pessimistic and  believed that it was impossible to ever detect the existence  of  black hole in deep space.  And then Prof Stephen Hawking  proposed that certain radiation would emit  from black holes which could be detectable.  Rumour is that he came up with this brilliant idea while reading " Men are from Mars, Women are from Venus". 

Like a football field, black hole also has a boundary called 'event horizon'.  This event horizon is a 'point of no return' because once light particles and any unfortunate person  enter this boundary they will be sucked into the centre of the black hole  and never able to escape.  It is a one way ticket.   Before we move on further,  I need to  explain something about a true vacuum.  Traditionally, you may think of  vacuum  as  space void of anything.  But in a vacuum like space, particles are constantly created from void, only  to be destroyed again in split second.  These are called....yea, you're right, virtual particles.  They always come in pairs.  One particle can be a negative charged electron (matter) and the other a positively charged positron (antimatter).  They pop out from nowhere, and annihilate ( 解體) when they bump into each other again  within a billionth of a second they are created.  They are called virtual particles because even in the billionth of a  second that the pair exists, they do not add any net mass to the universe because one particle  is matter and the other antimatter .  The pair just cancels each other out and therefore is a zero sum to the universe.  Just imagine the nachos and beer you consumed last night while watching NBA were made from virtual particles without mass, would that be nice?.

Now, something interesting happens at the very edge of the event horizon - imagine a pair of virtual particles pops into existence right at the boundary.  One particle jumps inside the event horizon and absorbed by the black hole, not to be seen anymore.  The other one, without its counterpart to annihilate it, escapes into space and becomes a real particle of its own right.  And because it now exists in the real world, it can be detected as radiation.    So, what do you think?  A black hole isn't black after all because at the edge of it there  is certain kind of radiation  emission which can be detected  at a distance.  This is one of the most important discovery by Stephen Hawking  and for this he is hailed as the greatest mind after Einstein by  many scientists. With this discovery researchers are now actively engaged in  searching for evidence of black holes in space.  So what?  - You may ask.  Well, all the modern theories in cosmology require the existence of black hole.  The discovery of one will be a major piece of evidence to support modern physics.

If you are still with me, I have a little secret that Stephen Hawking didn't tell you.  Imagine that virtual particle we've been talking about is a football Beckham  kicks into the net.  It spins clockwise (oh, you don't know all particles spin?)  and bingo....into the black hole.  Lets say that ball is an electron.  And now the anchor rewinds the footage. You will see the ball in reverse motion, spinning anticlockwise and return to Beckham right feet.  You are watching a football game running backward in time.  What is intriguing is this backward motion looks identical to the behavior of a  positron  escaping from the event horizon.  Ah, I can see from your expression you are confused.  No problem.  A positron, being antimatter, is an exact opposite copy of electron and  therefore  it has to  spin anticlockwise whereas an electron spins the opposite direction.  So  to  scientists and any  observer  a positron is actually an electron running backward in time.  The greatness of Stephen Hawking's theory of black hole isn't black is that if we, as observers nearby, happened to see radiation emission (suppose a positron) coming out from  the event horizon as described in the last paragraph, we are actually observing something (electron) running backward in time ?seeing a footage of an electron runs into the black hole in reverse. 

Isn't that amazing?  I think that is amazing.   I apologize if I cannot explain science as interesting as Hawking does.  I thank you for your patience in reading these lines and since you are still awaken, I want to move on to my next topic - "The Origin of Species".   Hey, I haven finished.  Wait! Wait!

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