JOHN MEANEY

17.3.14

BANG!

Some 13.7 billion years have passed since the Big Bang. That means that 13.7 billion years ago, everything (Every Thing) was stuck together in a singularity. According to the way people thought when the notion of a Big Bang was first accepted, the furthest away two objects could be from each other now (in the visible universe) is 13.7 billion lightyears, on the basis that the "cosmic speed limit", aka the speed of light, means that the furthest you can go in a year is one lightyear.

And then redshift measurements showed the universe is quite a lot bigger than that.

Some years back, I was teaching Computer Stuff to a bunch of code ninjas with brains the size of Jupiter, all of them smart enough to get physics jokes. So at one point, I gave a little ten-second riff on inflation theory:

According to relativity theory, nothing can travel faster than the speed of light. And according to inflation theory, that's exactly what the nothing did.

To my surprise, one of the guys said he'd puzzled over cosmic inflation as a physics student, and I'd just made it totally clear! (I'd thought I was merely being a smart-arse to relax the mood for a moment.)

In case you don't know about this stuff already, the point of inflation is that it's the spacetime-stuff itself that expanded. Lightspeed is the speed limit for anything travelling inside the medium that is spacetime; the medium itself can expand as fast it likes.

I grokked this early on because I'd previously been puzzled by explanations of cosmic redshift that refer to it as the Doppler effect. It really isn't. The equation for the wavelength/frequency shift is the same, but the model is different: the sound of a train approaching and then receding changes in pitch because of the motion of the train. Cosmic redshift is due to the expansion of spacetime itself, not the motion of stars through spacetime. Very, very different.

And of course, I mention it now because of the strongly named BICEP2 experiment at the South Pole that's discovered polarisation in the cosmic microwave background radiation that seems to be the "footprint" left by cosmic inflation when the universe was brand new.

On the other hand, the effect is rather stronger than predicted (originally by theoretical physicist Leonid Grishchuk at Cardiff University, Cardiff being one of the BICEP2 participants). Hope that doesn't mean it's like those little espresso neutrinos sniffing the Italian CERN coffee and breaking the speed limit except that they really weren't...

4 Comments:

Blogger Chris Barker said...

Hi John,

Every week I (almost) religiously trawl through Science's table of contents, and browse what takes my interest.

Since I started writing this SF stuff again, I've been paying attention outside my field (biochemistry) to the space stuff. The level at which I have any chance of understanding is in the Perspectives section in which an overview of a current paper is given.

Last week I was really taken by the 'cosmic inflation' discovery you mention. So I read this blog post with great interest. And almost miraculously, my poor biochemist's brain understood several things about the Big Bang which had hitherto left me slightly mystified (OK more than slightly!).
I wish you were my physics teacher! Perhaps I should delve back into your past blogs and learn some more ;)

March 30, 2014 at 6:14 PM  
Blogger John Meaney said...

Cheers, Chris!

And, er, thank you... I should use this power only for good. I wish you could teach me some biochemistry! I don't suppose you're in Gothenburg at the weekend, by any chance?

Ta loads!

March 31, 2014 at 3:39 PM  
Blogger Chris Barker said...

Alas, John I won't be there.
I'm saving my pennies (kronor) for my WorldCon trip in August.

Hope you have (had) a great time!

Chris

April 3, 2014 at 11:32 AM  
Blogger John Meaney said...

Ta loads... I was hoping to learn some Swedish for this trip, but no time. Should be fun anyway!

April 3, 2014 at 8:51 PM  

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