Have you ever heard about the “multiverse”? Let’s take a look at how our universe could potentially have a twin. #astrophysics
The material universe we know, which means the one astronomers have been studying, is likely flat. I know, it sounds like we are paraphrasing the “Earth is flat” belief from hundreds of years ago, but when it comes to the universe, its topology requires a different geometry.
How can we know it’s likely flat then? Well, if you’re in a square room (flat) and walk around the corners, you’ll return to your starting point having made four 90-degree turns. You can say that your room is flat. This is called Euclidean geometry.
But if you make the same journey on the surface of the Earth (sphere). Start at the equator, make a 90-degree turn, walk up to the North Pole, make another 90-degree turn, return to the equator, another 90-degree turn and return to your starting point.
In one situation, you made four turns to return to your starting point, in another situation it only took 3. That’s because the topology of the surface you were walking on decided what happens when you take a 90-degree turn.
When it comes to the universe, imagine flying out into space on a rocket for billions of light-years, performing 90-degree turns and returning to your starting point.
You can’t do it in three, or five, you need four, which means that the topology of the universe is flat. Which is totally intuitive, right? I mean, that would be your assumption.
In order to prove the flatness of the universe, you would need to travel a long way. And astronomers use the largest possible observation they can make. The cosmic microwave background radiation, the afterglow of the Big Bang, visible in all directions as a red-shifted, fading moment when the universe became transparent about 380,000 years after the Big Bang.
When this radiation was released, the entire universe was approximately 2,700 C. This was the moment when it was cool enough for photons were finally free to roam across the universe. The expansion of the universe stretched these photons out over their 13.8 billion year journey, shifting them down into the microwave spectrum, just 2.7 degrees above absolute zero.
With the most sensitive space-based telescopes they have available, astronomers are able to detect tiny variations in the temperature of this background radiation.
These tiny temperature variations correspond to the largest scale structures of the observable universe. A region that was a fraction of a degree warmer become a vast galaxy cluster, hundreds of millions of light-years across.
The cosmic microwave background radiation just gives and gives, and when it comes to figuring out the topology of the universe, it has the answer we need. If the universe was curved in any way, these temperature variations would appear distorted compared to the actual size that we see these structures today. But they’re not. To best of its ability, ESA’s Planck space telescope, can’t detect any distortion at all, proving that The universe is (likely) flat.
But if space-time goes on forever, then it must start repeating at some point, because there are a finite number of ways particles can be arranged in space and time.
So if you look far enough, you would encounter another version of… you! In fact, infinite versions of you. Well, it is a theory after all. Some of these versions of you would be doing exactly what you’re doing right now, while others would be having totally different lives.
This was a cosmologist point of you. Stay tuned for a more mystical theory for multiverse and parallel universes!