What Was Cosmic Inflation? The Quest to Understand the Earliest Universe

The Big Bang was a tremendous theory, but it had a few problems. In 1980 Alan Guth developed the revolutionary theory of cosmic inflation, and astronomers have been looking for evidence to this day.

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Karla Thompson - @karlaii

The Big Bang. The discovery that the Universe has been expanding for billions of years is one of the biggest revelations in the history of science. In a single moment, the entire Universe popped into existence, and has been expanding ever since.

We know this because of multiple lines of evidence: the cosmic microwave background radiation, the ratio of elements in the Universe, etc. But the most compelling one is just the simple fact that everything is expanding away from everything else. Which means, that if you run the clock backwards, the Universe was once an extremely hot dense region

Let’s go backwards in time, billions of years. The closer you get to the Big Bang, the closer everything was, and the hotter it was. When you reach about 380,000 years after the Big Bang, the entire Universe was so hot that all matter was ionized, with atomic nuclei and electrons buzzing around each other.

Keep going backwards, and the entire Universe was the temperature and density of a star, which fused together the primordial helium and other elements that we see to this day.

Continue to the beginning of time, and there was a point where everything was so hot that atoms themselves couldn’t hold together, breaking into their constituent protons and neutrons. Further back still and even atoms break apart into quarks. And before that, it’s just a big question mark. An infinitely dense Universe cosmologists called the singularity.

When you look out into the Universe in all directions, you see the cosmic microwave background radiation. That’s that point when the Universe cooled down so that light could travel freely through space.

And the temperature of this radiation is almost exactly the same in all directions that you look. There are tiny tiny variations, detectable only by the most sensitive instruments.

When two things are the same temperature, like a spoon in your coffee, it means that those two things have had an opportunity to interact. The coffee transferred heat to the spoon, and now their temperatures have equalized.

When we see this in opposite sides of the Universe, that means that at some point, in the ancient past, those two regions were touching. That spot where the light left 13.8 billion years ago on your left, was once directly touching that spot on your right that also emitted its light 13.8 billion years ago.

This is a great theory, but there’s a problem.

The Universe never had time for those opposite regions to touch. For the Universe to have the uniform temperature we see today, it would have needed to spend enough time mixing together. But it didn’t have enough time, in fact, the Universe didn’t have any time to exchange temperature.

Imagine you dipped that spoon into the coffee and then pulled it out moments later before the heat could transfer, and yet the coffee and spoon are exactly the same temperature.

What’s going on?

To address this problem, the cosmologist Alan Guth proposed the idea of cosmic inflation in 1980. That moments after the Big Bang, the entire Universe expanded dramatically.

And by “moments”, I mean that the inflationary period started when the Universe was only 10^-36 seconds old, and ended when the Universe was 10^-32 seconds old.

And by “expanded dramatically”, I mean that it got 10^26 times larger. That’s a 1 followed by 26 zeroes.

Before inflation, the observable Universe was smaller than an atom. After inflation, it was about 0.88 millimeters. Today, those regions have been stretched 93 billion light-years apart.

This concept of inflation was further developed by cosmologists Andrei Linde, Paul Steinhardt, Andy Albrecht and others.

Inflation resolved some of the shortcomings of the Big Bang Theory.

The first is known as the flatness problem. The most sensitive satellites we have today measure the Universe as flat. Not like a piece-of-paper-flat, but flat in the sense that parallel lines will remain parallel forever as they travel through the Universe. Under the original Big Bang cosmology, you would expect the curvature of the Universe to grow with time.

The second is the horizon problem. And this is the problem I mentioned above, that two regions of the Universe shouldn’t have been able to see each other and interact long enough to be the same temperature.

[MrBengourben]

Hi Fraser. Another great video. I've been watching these, and the great Weekly Space Hangout, for years now. Its the first time I've been prompted to ask a
question; What would our universe be like now if inflation had never happened?
Fantastic work, and I for one really appreciate the effort that goes into these great educational shows.
Thanks.

[johnspadaro]

Hey Fraser, I don't have a question I just wanted to say thanks for making these awesome videos I always really enjoy them.

[MrKago]

I was watching you earlier video and you mentioned that if some of the bacteria on Earth had a reliable source of energy they could thrive on Mars. They would have plenty of energy in the perchlorates that are in the ultra fine dust on Mars. My question is what are all these people who want to go to Mars planning to do about these toxic perchlorates?

Another really really good series of videos is Carolin Crawford's lectures at Gresham College. She explains difficult things so well. Her lecture on the early universe is awesome.

[AvyScottandFlower]

Hey Fraser, could other universes be contained beyond/inside the event horizon of a black hole? Ours too, maybe, in a retroactive way?

Another one for your Q&A :P Hope to jump into the live one again, too!

[dnranjit]

As you rightly mentioned, BICEP2 had to retract their result on the B-modes being polarized due to GWs.
So the comic inflation theory is not yet proved. We may have to wait for a decade or two for GW detectors to get more sensitive or better polarization measurements from other results.

[truebaran]

huuuuge request: please make a (advanced) video about falling into rotating/charged black hole, there are pleny of videos on youtube about falling into black hole, most of them quite inaccurate and none is adressing the case of charged and rotating black hole. I would be very grateful

[hdy]

Hi Fraser, Ive always struggled with the concept as it seems like a plaster over a gaping problem, are there any credible alternative theories to the big bang?

[Hobo_X]

You could talk about GUT and quantum gravity and the problems/solutions they give?

[larnotlars]

2 things are confusing me about this segment. I know that they stem from a combination of my lack of background but I can't get my head around them.

1- Having the Cosmic Background Radiation at the same temperature: Does it have to be conduction transfer of energy, why is it obviously not that the birthing of the big bang came at a uniform temperature that was inherent in the creation of quark progenitor particles? The act was obviously so massively exothermic that it could have reached some temperature threshold that everything was pegged at the top of the cosmic thermometer?

2- Every graph that I have seen to demonstrate cosmic inflation, shows a sideways bell curve with massive growth followed by flatter growth that ultimately becomes logarithmic. Less than a millimeter? I am prone to exaggeration, but I don't think that even a politician would find the diagrams of cosmic inflation to be acceptable. I think that it would look more like the worlds sharpest spear!

Lar

[hannahlegaspi]

This was the only cosmic inflation video that I perfectly understood. Thaaaanks

[UpcycleElectronics]

1.) If we could traverse the galaxy, what locations would make our top 3 list of places to explore?
2.) Would these locations appeal to observers from any direction?
3.) Why don't we pick the nearest safe location for sending a time capsule type probe to these locations and send them?
Even if it takes millions of years to get there couldn't we pick a location that practically guarantees an encounter?

Can we put aside the fear of advanced invaders and instead think legacy and being remembered for more than our mineralized bones?

[js]

On the one hand cosmologists talk about the big bang and on the other they talk about black holes. Our own galaxy has a supermassive blak hole said to have the mass of billions of suns. Ant star about 10 times the mass of our own sun is said to eventually collapse into a black hole. Here what I am puzzled about:
Given the total mass in the universe, why is the mass so dispersed? Why did it not coalesce into one supreme black hole instead?

[OnekiKai]

+Fraiser Cain Would the CMB look the same for observers elsewhere in the universe?

[pleasestaysafe]

HUGE QUESTION! With the upcoming total eclipse, I live in an area that will be able to view it is it worth driving 5 hours over to the area where it will be in totality? Specifically, will the Stars and planets visible in the .9 area? or is Dark Skies only a result of being in the 70 mile total darkness area?

[NicosMind]

If everything starts at max temperature, then expands, then why does it need to mix to be the same temperature? Surely theres no mixing needed. The similarity in temperature of the CMB could be explained because of its starting heat?

[brendansully]

A little above my head on this one, but great video none the less.

[hallowacko]

I read in a science article once that someone had a well supported hypothesis that gravity acted far different in the conditions of the extremely early universe, acting as the repulsive force of inflation. though i suppose that would work more on the matter than the spacetime, right?

[cloneskiller]

why are people saying the pictures of earth are fake, clearly they are wrong on how things work.

[ncott]

can you help me understand why scientist say the universe is flat. I'm really confused because obviously we aren't flat so how can the universe be flat?

[kurtreber]

Hi Fraser,
If all known atomic/sub-atomic particles in the universe could physically touch (no space between nuclei and their electrons, etc), how much space would it take up? Equivalent to one galaxy? to one star system?