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What Physics Recently Discovered About the Big Bang

You've probably heard about the recent discovery made by scientists in the South Pole. But what was it exactly and what does it mean for us? Math Dude explains.

By
Jason Marshall, PhD,
April 11, 2014
Episode #194

As you may have heard, an international team of physicists recently discovered something called “B-mode polarization” imprinted in the glow of light left over from the Big Bang. If you heard that, you probably also heard that this discovery directly supports the idea that something called “inflation” occurred in the tiniest fraction of a second after the Big Bang. And if you heard all of that, you almost certainly heard that all of this means that we’ve finally pinned down exactly what happened in the first unimaginably brief instances after the Universe began.

But are all of these things you may have heard really true? If so, what do they mean? And what’s the math that makes physicists believe (or perhaps not believe) them? Those are exactly the questions we’ll be talking about today.

Sponsor: This episode is brought to you by NatureBox. Discover smarter snacking with a new NatureBox each month. Get 50% off your first box when you go to naturebox.com/qdt.

The (Very) Basics of the Big Bang

Before we can talk about the recent discovery that’s been all over the news, we first need to talk about what’s called “Big Bang Cosmology.” In truth, this is a really, really, really complicated topic, so we’re just going to hit upon the most basic ideas. Our primary goals are simply to understand a bit of why physicists are so confident of their findings (spoiler alert: it has to do with math) and to come to grips with the significance of those findings.

At First, There Was the Universe...

The most important thing to know is that there is an abundance of evidence that supports the idea that the Universe as we know it began a little less than 14 billion years ago. While we can’t say what caused the Big Bang to kick off in the first place, thanks to the aforementioned recent discovery we rather amazingly now know exactly what happened from a mind-bendingly short time (0.00000000000000000000000000000000001 seconds) after the Big Bang up to the present day.

See also: What Is the Space-Time Continuum?

 

Besides giving rise to you, me, and everything else that we know and love in the world (which on a cosmic scale are really just tiny details), the most important thing that the Universe has been doing since the Big Bang is expanding…and expanding…and expanding.

What Is Cosmic Inflation?

And that expansion is exactly what the recent discovery was about. But it wasn’t about whether or not the Universe is expanding (that’s been well understood for a long time), it was about how it expanded in the very earliest moments of the Universe’s existence.

The problem is that when scientists look at the blanket of light—the so called Cosmic Microwave Background—which to this day carries a sort of imprint of the Universe as it appeared only 380,000 years after the Big Bang, they see that it is far too smooth. What does that mean? Well, the degree of smoothness has to do with how clumpy matter was at that time, and we know that matter should have been clumpier than what we see. Unless something happened to smooth out those clumps.

See also: Newton, Einstein, and Gravitational Waves

 

Enter cosmic inflation. As the name suggests, the idea is that for a fleeting instant the nascent Universe underwent a sort of spasm during which its rate of expansion accelerated wildly so that in the span of a bit more than a billionth of a trillionth of a trillionth of a second it increased in size by a factor of 100 trillion trillion trillion trillion. In other words, it got comparatively really big really fast. And that rapid period of expansion was enough to smooth out the initial clumpiness and leave us with the smooth Cosmic Microwave Background that we see today.

What's New About the Big Bang?

Or at least that’s what physicists and astronomers believed must have happened. But the truth is that although this inflationary hypothesis (as it was called) could provide an explanation for the smoothness problem and several others, there wasn’t any direct evidence that inflation really happened.

Until recently, that is. Because the discovery of direct evidence for cosmic inflation is exactly what was announced by a team of astronomers using the BICEP2 telescope located at the South Pole. (As a quick aside: Why the South Pole? Because it’s one of the driest places on the planet—which is important because atmospheric water vapor makes observations of the Cosmic Microwave Background pretty much impossible.)

The key idea that led to the discovery is the fact that if inflation happened, it would have produced something called gravitational waves (which are pretty much exactly what they sound like), and those gravitational waves would have produced twisty curls—so called B-mode polarization—in the Cosmic Microwave Background.

Twisty curls? Those are exactly what the BICEP2 team observed. So, bingo!

Why Do Physicists Believe the BICEP2 Results?

Should we believe the BICEP2 results? Yes. Why? Because math is on their side. And in particular, statistics is on their side.

As the BICEP2 team state in their FAQ:

"We have detected B-mode polarization at precisely the angular scales where the inflationary signal is expected to peak with very high significance (> 5 sigma). Inflationary gravitational waves appear to be by far the most likely explanation for the signal we see."

The phrase "high significance" is extremely important here. Why? Well, it goes back to the fact that measurements aren't perfect and always have some uncertainty associated with them. Whenever a measurement is taken (in this case we're talking about measuring photons from the Cosmic Microwave Background), there is always a possibility that a result is obtained by chance and that repeating the measurement could give a completely different result.

For a >5 sigma detection, the probability that a result has occurred purely by chance is about 1 in 3.5 million. Which is a pretty small chance. And that's exactly why the BICEP2 team is confident of their results.

Having said that, although it seems unlikely, there is always a chance that there is some systematic error in the data that is conspiring to trick us. Which is precisely why many other teams will soon be (or already are) repeating these observations with their own equipment to confirm the results. But for now things are looking pretty rock solid.

Why Does this Discovery Matter?

While that’s all well and good, you might be wondering why you should care about any of this. After all, it’s not going to have any practical influence on your life today, tomorrow, or even next year, right? 

I have two answers for that. The first is kind of silly but nonetheless true. And that is that you should care because this stuff is really, really cool. Seriously, think about it—we humans now understand the big picture view of how the Universe has evolved almost from the moment it was born up to the present day. That’s mind-boggling.

And the second—much more practical—answer comes from an article that my favorite astronomy blogger, Phil Plait, wrote for slate.com. Phil writes:

"Inflation is based on principles of quantum mechanics, while gravitational waves are the purview of relativity. QM has brought us computers, solar power, atomic energy—a huge amount of modern tech. Relativity is critical in many aspects of our lives as well, including GPS and nuclear power. In the past these two concepts haven’t played well together, but now we have a direct and profound connection between them. This result is new, and we have a long, long way to go to understand it better. There’s no way to know what will result from this. Yet. But whenever we open up new fields of science, all sorts of interesting things follow. Bet on it."

Wrap Up

Okay, that's all the math, astronomy, and all-around cosmic awesomeness we have time for today. Check out Everyday Einstein's episode Newton, Einstein, and Gravitational Waves for more about the back story of this fascinating discovery.

Please be sure to check out my book The Math Dude’s Quick and Dirty Guide to Algebra. And remember to become a fan of the Math Dude on Facebook where you’ll find lots of great math posted throughout the week. If you’re on Twitter, please follow me there, too.

Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!

BICEP2 telescope image from the Steffen Richter, Harvard University. BICEP2 B-mode signal image from the BICEP2 collaboration.

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