Why Stephen Hawking’s Multiverse Paper is (not that) Interesting

On may 2nd Stephen Hawking’s final paper was released after his death a few months earlier. The paper’s name, “A Smooth Exit from Eternal Inflation?” Takes on the idea of a multiverse — so obviously there’s been a lot of attention. Hawking is undoubtedly one of the top 5 minds of all time when it comes to astrophysics. However, that doesn’t mean that his latest paper deserves to be heralded as ‘solving the multiverse paradox’. So it’s time to examine Hawking’s latest paper and try to shed some on light on whether or not we should care about it.

The multiverse theory is just one of many theories of how the universe started. Like most things in space, you need to have a foundational knowledge of the different theories of how the universe started before we can soundly make said judgment about Hawking’s paper.

(the following are a somewhat random sampling to show the trajectory of thinking on this)

pTolemy universe

2nd Century BC

Gotta start somewhere. We thought the earth was the center of the universe, created by god, and postulated that all ‘heavenly bodies’ i.e. the sun and the moon revolves around the earth in predictable, circular motions.

Kepplers universe

1500’s AD

You’ll notice a pretty big gap here. The catholic church wasn’t too pleased with progress in this area. In this model the sun was the center of the universe, created by god, but planets moved faster when they were closest to the sun. Thus the idea of gravity starts bouncing around among the smartest people who thought about this.

Theory of Relativity

Einstein 1905

This is on here because it’s probably the biggest discovery in the history of space. Won’t get into it anymore. But here’s a good summary.

Freidman’s universe theory

1922 (But for the sake of time I’m putting a bunch of other stuff in here too)

He believed that Albert Einstein’s general theory of relativity required a theory of the universe in motion, as opposed to the static universe that scientists previously believed. This meant that the universe was either small at one point and getting bigger, or was much bigger and is getting smaller. As you can imagine the latter would be bad. Very, very bad. (Note: It would be bad for humans and animals and general life. Right now the universe is expanding at a pretty predictable clip. But if that changed, or the universe became unstable due to gravitational forces (there’s some complicated dark matter implication here), the universe could start contracting. Eventually, the universe would have a big crunch. Think of this as basically a big bang that would shrink our universe down to that 1 / 1,000,000,000 of a pin prick and be 10B degrees.)

This had some pretty important implications. It meant that the universe had a starting point. The best way to think of this starting point is as a really hot (~10 Billion Degrees F) small (1/1,000,000,000 of a pin prick) ball of dense matter that exploded and cooled really quickly and made everything we know as the universe.

This was a very big discovery. However it created a question that hurts to think about. If the universe had a beginning, and expanded through space and time and this dense matter expanded and cooled…then what was there before the universe? What is there if you have no space and no time? What do you call that? How does matter and dimensionality just start? Where did our laws of physics come from that governed this whole thing in the first place?

5th Dimension theory from Paul Steinhardt

Ongoing from the 70’s & 80’s

Paul Steinhardt agreed that there was a big bang, but also said that there was no beginning to the universe. He claimed these big bangs were happening all the time — but in a 5th dimension that we can’t perceive. All of space and time as we know it sits on a four-dimensional surface called a brane. Sometimes it collides with another universe brane, and the smash creates bursts of energy that we would define as a big bang. As the universes move farther and farther apart in the fifth dimension, our universe expands. The idea is that these collisions and expansions go on forever.

Multiverse Theory Part 1 aka eternal inflation (**side note to read at end of article)

By 1979 there is general consensus that the investigation of parallel universes should be undertaken as a serious endeavor (source: cbsnews.com)

1979, A bunch of people

The multiverse theory has taken many forms and been around for some time. But we are going to focus on a few specific points of the more contemporary theories.

The idea that multiple parallel universes exist originates out of inflation, the very fast expansion of the universe right after the Big Bang, that included a lot of explosions that sent the universe expanding faster than the speed of light (wait I thought nothing could be faster than the speed of light?). Many scientists think during these explosions, there were quantum level packets of energy, which grew into larger pockets of space time. This effect essentially created individual universes that are housed within an ever expanding multiverse

In this model, each universe has a big bang and keeps its own time. In the most popular version, each universe might even have its own version of physics too. Infinite possibilities yield infinite results.

Hawking and crew doesn’t really like this idea that there infinite possibilities and each universe may be subject to its own laws of physics.

This theory is not falsifiable, because everything is possible the virtue of traditional physics is that its theories could be falsified by experiments. Science is a learning experience. If we give up on the possibility of falsifying our ideas, then we will not learn anything from experiments.

Multiverse Theory Part 2

2018 Hawking

At this point everyone is basically agreeing that there are multiple universes. Let’s just all agree that that idea is inconceivable and move on. The main arguments now has to do with:

1. How many universes are there
2. What laws govern them

This is really the crux of Hawking’s new paper. He created a framework for the multiverse that is “simpler”. This version limits how many new universes could form, and ensures they adhere to the same laws of physics as our known universe.

Basically the main difference in Multiverse theory 2 vs. Multiverse theory 1:

“It’s like you have a bath full of lots and lots and lots of different kinds of soap bubbles and each soap bubble is a different universe, and there’s a huge variety of different soap bubbles of different shapes,” says Clifford Johnson, a professor in the Physics and Astronomy Department at the University of Southern California. “And what this model is suggesting is a mechanism by which maybe the variety of soap bubbles that are available is not as large as was thought.”

The reason that this is important is that it makes the number of universes finite. When things are finite you can use complicated math to figure things out like: why does our universe look like it does, how and why was life created etc. But when the assumption is that universes are infinite, everyone just throws their hands up because probability and other math stuff doesn’t work on infinity.

Overall, since this new proposal is using math to once again be able to use math (from infinity to finite), this also is not falsifiable. This means it likely won’t substantially push our understanding of the universe forward very much…at least at this moment.

So while this was cool to read about — the verdict is that this really isn’t that big of a deal.

**Side note that I think is cool.

One major arguments for the multiverse theory is that the odds that a single big bang occured with the perfect conditions for life is extremely unlikely. However when you look at the composition of the universe in rank order of abundance:

1. Hydrogen
2. Helium
3. Oxygen
4. Carbon
5. Nitrogen

And compare that to the composition of earth, you find that it may actually be more likely that life is inevitable.

Earth is mostly water (Hydrogen and Oxygen — two of the most abundant molecules in the universe).

Even if you look at humans we are essentially reflections of what’s going on in the universe — with the exception of helium. And helium won’t even kill you.

1. Hydrogen (matches universe)
2. Oxygen (matches universe)
3. Carbon (matches universe)
4. Nitrogen (matches universe)

So maybe, just maybe, it wouldn’t take a statistical oddity for life to crop up. Maybe given enough time (and space) life is actually inevitable. This would mean that it wouldn’t necessarily take infinite universes to create life.