There may be other worlds out there. Where there could be an exact copy of our solar system, our Earth and each one of us. The Universe s3e2: Parallel Universes, History 2008
The universe sits in a sea of parallel universes. ibid.
Remarkably, there may be four types of parallel universe out there: one could exist in exactly the same space that we are in, but it is so far away we cannot see it or reach it. In another scenario, multiple giant universes could exist in giant cosmic soap bubbles adrift in a cosmic sea of giant bubbles. In yet another scenario, many parallel universes occupy the same space and times as our universe, but because they are in different dimensions, they are invisible. In yet another, all the laws of physics are different so everything looks completely different. ibid.
The Wmap seems to show that the universe is flat. ibid.
‘We are children of the bubble.’ ibid. Tegmark
When in the 1980s scientists came up with a lyrical-sounding idea – String Theory – it promised to solve all the mysteries of the universe, including whether or not parallel universes are real. The idea is that all particles are not solid points or dots, as science said they were. Instead, if you could see up close, particles are in fact tiny string-like objects that individually vibrate in various ways ... String Theory has now evolved into M or M-brane Theory. ibid.
The crowning achievement of M Theory came when scientists realised that to make sense of everything, you need to think of the universe as existing in eleven dimensions. M Theory explains how the tiniest as well as the biggest things in the cosmos work. It also proposes that we all live on a giant and energetic M-brane. Our universe is tethered to this wall by extra dimensions ... These M-branes are also very close to each other. ibid.
One obscure and oddball idea seemed to require for consistency the existence of extra dimensions. This idea was String Theory. String Theory has a justified reputation as a difficult and complex subject. The Entire History of the Universe e16: Where Are All the Hidden Dimensions? 2021
Most scientific theories do end up dead and forgotten. The Entire History of the Universe e23: Have We Really Found the Theory of Everything?
Gradually, the lights went out for Steady State. ibid.
Regular conferences are being held packed with both young and old attendees, all chasing the holy grail of physics – a unified theory that explains it all. ibid.
What was more, said Witten, M Theory was 11 dimensional, not 10, and the fundamental objects of this 11 dimensional theory were no longer strings, but a mysterious object taken from supergravity, the sixth theory. The fundamental objects of M Theory were branes – more specifically M-branes. ibid.
M Theory: A world of strings born from wrapping higher dimensional branes around minuscule extra dimensions. ibid.
For there is absolutely zero direct experimental evidence for M or String theory. ibid.