Making Sense of Science
   
April 2010
 
 


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Was There Really a Big Bang?

Did matter, time and space suddenly burst into existence 13.8 billion years ago in an explosion that lasted about 3 minutes, as scientists say?  Or is it "just a theory"?
 
Every proper scientific theory must have evidence to support it.  In science-speak, "theory" actually means "an established framework" and is not nearly as flimsy a thing as the word implies.  A theory is not just any crazy idea: it must meet certain criteria.  If the idea can be tested, it is formed into an hypothesis.  An hypothesis graduates to Theory status only when 1) there is substantial evidence to back it up, 2) when it demonstrates predictive ability, and 3) after any possible evidence against it has been searched for but not found.  Finally, every possible alternative has to be thoroughly explored before the new theory will be widely accepted.

And then there's the unimaginative name.  "The Big Bang" was originally coined as a term of derision by people who didn't think it would ever make it as a theory.  But as the evidence for it mounted, the name stuck.  I am a fan of cartoonist Bill Waterson's improved name for this theory, "The Tremendous Space Kablooie,"  but I am in the minority on this point.

For something as impossible-sounding as the Big Bang Theory, there'd better be some darn good evidence.  Are you ready to find out what it is?

 

None of us were there, so what makes us think there might have been a Big Bang?  The first clue is all around us:  Matter.  We now know matter is composed of large numbers of just three basic parts: protons, neutrons and electrons.  (Please Visit my blog for an explanation of the structure of matter.) 

The next logical step is to figure out where those pieces came from.  Electrons, for example, are formed when a particle of light in the high x-ray range or beyond suddenly disappears, leaving an electron and its arch-nemesis, the anti-electron, behind.  Like being born with an evil twin. 

How do we know this?  By experiment.  Anyone can do it - all you need is a source of x-rays and a way of recording what happens next.  This DIY cloud chamber can help.  But since x-rays can sometimes be dangerous to your health, best leave it to the pros.

Electrons and anti-electrons usually destroy each other and turn back into a flash of light.  However, a tiny fraction of anti-electrons are "defective" in some way that we're still trying to discover (much like a certain brand of import car).  A miniscule percentage of them break down, leaving single electrons free to exist unmolested by their evil twins.  Those lucky ones survive to this day and comprise everything we know in and around us. For more information about this enthralling mystery of modern Science I recommend the book The Mystery of the Missing Antimatter by Helen Quinn and Yossi Nir.

For so many electrons to exist in such numbers, the universe must have been very hot, dense and full of x-rays at some time.  Apparently it didn't stay that way because, well, here we are.  The conditions favouring electron production are obviously not prevalent in the universe we know today.  One might ask, "Why was it so before, and why isn't it so now?"  This provides us with the first inkling that we inhabit an ever-changing universe.

The next clue was stumbled upon by investigators doing spectrophotometric chemical analysis of distant galaxies. (Yes, amazingly, there are people who do that sort of thing.  Why?  Because they're scientists.) 

It was noticed that the wavelengths of light coming from distant galaxies were always longer than they ought to be, and by a fairly predictable amount.  The further away a galaxy was, the more stretched out the wavelengths were.  Finally someone correctly deduced that this was an intergalactic example of the Doppler Effect.  A train's horn seems to have a higher pitch when it is coming towards you, and a lower pitch when receding from you, even though nothing about the horn actually changes as it speeds past. 

The inescapable conclusion was that all galaxies are spreading out from each other in an expanding space.  And if that is happening now, they must have been closer together in the past.  In fact, there must have been a "time zero" when the universe was infinitely dense and hot; hot enough to cook up billions of galaxies-worth of matter.

From their observations, Astronomers have worked out when that "time zero" was:  13.8 billion years ago.

But where's the smoking gun?  If such an event really took place, it must have left some trace or imprint, some detectable feature on the universe, some afterglow or reverberation.  If the Big Bang consisted of a massive flash of light, where is that light today?  Shouldn't we still be able to see it way off in the distance? 

Actually, we can.  The theory predicts that this afterglow should show up in the microwave part of the spectrum.  When we tune in with microwave antennas, there is a faint background hiss coming from all directions that never goes away.  To someone with "microwave eyes" the Big Bang can still be seen in the sky surrounding us, and it looks like this:

Image: COBE Project and NASA

Want to know more about the Big Bang?  I'd like to personally recommend to you one of my favorite books, The First Three Minutes: A Modern View Of The Origin Of The Universe by Steven Weinberg.  I first read it in 1989, and the book has only become better with the continued expansion of the universe. 

Best Regards,

John

 
 
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