Post by swamprat on Jun 22, 2020 16:47:30 GMT
Time for another headache.....
Why some physicists really think there's a 'mirror universe' hiding in space-time
By Rafi Letzter - Staff Writer 22 June 2020
What happens if you turn space-time upside-down?
The Cosmic Microwave Background, pictured here, is the most ancient thing we can see in space. But what's hiding behind it? (Image: © ESA and the Planck Collaboration)
A series of viral articles claimed that NASA had discovered particles from another parallel universe in which time runs backward. These claims were incorrect. The true story is far more exciting and strange, involving a journey into the Big Bang and out the other side.
The sensational headlines had muddled the findings of an obscure 2018 paper, never published in a peer-reviewed journal, which argued that our universe might have a mirror reflection across time, a partner universe that stretches beyond the Big Bang. If that's the case, and a series of other extremely unlikely and outlandish hypotheses turn out to be true, the paper argued, then that in turn could explain a mysterious signal hinting that a completely new particle is flying out of the ice in Antarctica.
The claim that NASA discovered a parallel universe seemed to have been first dreamed up by British tabloid The Daily Star, and the story was then picked up by British and American outlets, including The New York Post.
Screenshots show false "parallel universe" claims in several publications. (Image credit: Illustration by Live Science)
Our universe's "mirror"
In order to understand how The Daily Star arrived at its bizarre, viral claim, it's necessary to understand the claims of two separate papers from 2018.
The first paper, by Latham Boyle, a physicist at The Perimeter Institute in Alberta, Canada, and his colleagues, proposed a mirror universe — a reflection of our universe across time. It was published December 2018 in the journal Physical Review Letters (after an appearance on the arXiv server in March that year).
"I think nobody else understands the full sweep of what they have composed," said John Learned, a University of Hawaii astrophysicist and the co-author of a second paper, which builds on Boyle's theory.
Boyle's work is a kind of expansion pack meant to plug holes in the theory that tells the dominant origin story of the universe: Lambda-Cold Dark Matter (ΛCDM).
ΛCDM explains the cosmos using two key ideas: An unknown dark energy causes the universe to expand. Rewind that expansion far enough backward in time and the whole universe occupies a single point in space. Second, an unseen dark matter gravitationally tugs on stuff in the universe, yet emits no light. This dark matter, the idea goes, accounts for the vast majority of the universe's mass.
"ΛCDM is basically the only game in town," Learned said. "It works in many cases, but there are some somewhat disturbing lapses in the modeling."
For instance, measurements of expansion don't line up across time, so that measurements made of this expansion based on data from the early universe don’t jive with measurements using data from the modern universe. In addition, ΛCDM can't explain why matter exists at all, since it predicts that matter and antimatter would have formed at equal rates after the Big Bang, and annihilated each other, leaving nothing behind.
Boyle and his colleagues' new universe unwinds the ΛCDM story further back in time, diving into the singularity at the beginning of time and coming out the other side.
Here’s how Boyle’s team sees their theory: Imagine today's universe as a wide, flat circle, sitting on top of yesterday's slightly smaller circle, which sits on top of the yet-smaller circle of the day before that, Boyle said.
(Image credit: Meghan McCarter)
Stack up all the circles from today back to the Big Bang, and you'd end up with a cone standing on its point end.
(Image credit: Meghan McCarter)
When astronomers look deep into space, they're effectively looking back in time. The most distant galaxy we can see, GN-z11, appears to us as it existed 13.4 billion years ago, or 400 million years after the Big Bang.
Before that, the universe had a "dark age" lasting millions of years, where nothing bright enough for us to see formed. Before that, the universe produced the oldest thing we can see: the Cosmic Microwave Background (CMB), which formed 370,000 years after the Big Bang, as the universe cooled out of a hot, opaque plasma.
Telescopes can't see anything from before the CMB.
Looking back in time like this, Boyle said, is like looking down through the cosmological cone.
(Image credit: Meghan McCarter)
Viewed in this way, the ΛCDM story ends with the universe coming together into a single point hidden behind the CMB. Boyle's theory looks at the opaque wall the CMB forms across time and draws a different conclusion about what the CMB hides.
The standard view, he said, is that the hot, dense era below the CMB (from our vantage point on the cone) was more or less a "big mess." In ΛCDM cosmology, this is the accelerated period of expansion known as "the epoch of inflation." Back then everything was chaos, the theory states.
But the CMB isn't that chaotic. Its simple structure, according to ΛCDM, emerged after an intense flattening process that wiped away the old mess.
"We were interested in exploring a simpler picture where you take the evidence more at face value," he said. "You say 'Okay, we can't see all the way down to the Bang, but we can look darned close, and as close as we look things look super simple. What if we take those observations at face value?'"
This vision of space-time still has a Big Bang hiding behind the CMB, he said.
But "it's much simpler than most of the singularities that arise in Einstein's theory of gravity," he said. "It's a very special type of ultra-simple singularity, where you can follow the solution [to the equations governing space-time] through the singularity."
Whereas observations go no further back than the CMB, normal cosmological models go a bit further back but still tend to come to a hard stop at the Big Bang. Not in Boyle's scheme.
"You find that it extrapolates, it extends — it analytically continues, physicists would say, to this double cone," he said, referring to the second universe extending away from the Big Bang in time.
(Image credit: Meghan McCarter)
"It just seems to be the natural, simplest extension of the equations that seem to describe the universe as we see it," he said.
This universe that’s inside the “second cone” is too far down space-time for us to see. Time might seem to run backward there from our reference frame, Learned said. But beings in that universe would still see cause coming before effect, just like we do in ours. Time runs away from the Big Bang in that universe, just like it does in ours. "Away from the Big Bang" in that universe is the opposite direction from the direction of time in our universe. but it doesn't run "backward" in the way we might imagine.
Our universe exists on the other side of that universe's ancient history, and that universe exists on the other side of ours.
Why some physicists really think there's a 'mirror universe' hiding in space-time
By Rafi Letzter - Staff Writer 22 June 2020
What happens if you turn space-time upside-down?
The Cosmic Microwave Background, pictured here, is the most ancient thing we can see in space. But what's hiding behind it? (Image: © ESA and the Planck Collaboration) A series of viral articles claimed that NASA had discovered particles from another parallel universe in which time runs backward. These claims were incorrect. The true story is far more exciting and strange, involving a journey into the Big Bang and out the other side.
The sensational headlines had muddled the findings of an obscure 2018 paper, never published in a peer-reviewed journal, which argued that our universe might have a mirror reflection across time, a partner universe that stretches beyond the Big Bang. If that's the case, and a series of other extremely unlikely and outlandish hypotheses turn out to be true, the paper argued, then that in turn could explain a mysterious signal hinting that a completely new particle is flying out of the ice in Antarctica.
The claim that NASA discovered a parallel universe seemed to have been first dreamed up by British tabloid The Daily Star, and the story was then picked up by British and American outlets, including The New York Post.
Screenshots show false "parallel universe" claims in several publications. (Image credit: Illustration by Live Science)Our universe's "mirror"
In order to understand how The Daily Star arrived at its bizarre, viral claim, it's necessary to understand the claims of two separate papers from 2018.
The first paper, by Latham Boyle, a physicist at The Perimeter Institute in Alberta, Canada, and his colleagues, proposed a mirror universe — a reflection of our universe across time. It was published December 2018 in the journal Physical Review Letters (after an appearance on the arXiv server in March that year).
"I think nobody else understands the full sweep of what they have composed," said John Learned, a University of Hawaii astrophysicist and the co-author of a second paper, which builds on Boyle's theory.
Boyle's work is a kind of expansion pack meant to plug holes in the theory that tells the dominant origin story of the universe: Lambda-Cold Dark Matter (ΛCDM).
ΛCDM explains the cosmos using two key ideas: An unknown dark energy causes the universe to expand. Rewind that expansion far enough backward in time and the whole universe occupies a single point in space. Second, an unseen dark matter gravitationally tugs on stuff in the universe, yet emits no light. This dark matter, the idea goes, accounts for the vast majority of the universe's mass.
"ΛCDM is basically the only game in town," Learned said. "It works in many cases, but there are some somewhat disturbing lapses in the modeling."
For instance, measurements of expansion don't line up across time, so that measurements made of this expansion based on data from the early universe don’t jive with measurements using data from the modern universe. In addition, ΛCDM can't explain why matter exists at all, since it predicts that matter and antimatter would have formed at equal rates after the Big Bang, and annihilated each other, leaving nothing behind.
Boyle and his colleagues' new universe unwinds the ΛCDM story further back in time, diving into the singularity at the beginning of time and coming out the other side.
Here’s how Boyle’s team sees their theory: Imagine today's universe as a wide, flat circle, sitting on top of yesterday's slightly smaller circle, which sits on top of the yet-smaller circle of the day before that, Boyle said.
(Image credit: Meghan McCarter)Stack up all the circles from today back to the Big Bang, and you'd end up with a cone standing on its point end.
(Image credit: Meghan McCarter)When astronomers look deep into space, they're effectively looking back in time. The most distant galaxy we can see, GN-z11, appears to us as it existed 13.4 billion years ago, or 400 million years after the Big Bang.
Before that, the universe had a "dark age" lasting millions of years, where nothing bright enough for us to see formed. Before that, the universe produced the oldest thing we can see: the Cosmic Microwave Background (CMB), which formed 370,000 years after the Big Bang, as the universe cooled out of a hot, opaque plasma.
Telescopes can't see anything from before the CMB.
Looking back in time like this, Boyle said, is like looking down through the cosmological cone.
(Image credit: Meghan McCarter)Viewed in this way, the ΛCDM story ends with the universe coming together into a single point hidden behind the CMB. Boyle's theory looks at the opaque wall the CMB forms across time and draws a different conclusion about what the CMB hides.
The standard view, he said, is that the hot, dense era below the CMB (from our vantage point on the cone) was more or less a "big mess." In ΛCDM cosmology, this is the accelerated period of expansion known as "the epoch of inflation." Back then everything was chaos, the theory states.
But the CMB isn't that chaotic. Its simple structure, according to ΛCDM, emerged after an intense flattening process that wiped away the old mess.
"We were interested in exploring a simpler picture where you take the evidence more at face value," he said. "You say 'Okay, we can't see all the way down to the Bang, but we can look darned close, and as close as we look things look super simple. What if we take those observations at face value?'"
This vision of space-time still has a Big Bang hiding behind the CMB, he said.
But "it's much simpler than most of the singularities that arise in Einstein's theory of gravity," he said. "It's a very special type of ultra-simple singularity, where you can follow the solution [to the equations governing space-time] through the singularity."
Whereas observations go no further back than the CMB, normal cosmological models go a bit further back but still tend to come to a hard stop at the Big Bang. Not in Boyle's scheme.
"You find that it extrapolates, it extends — it analytically continues, physicists would say, to this double cone," he said, referring to the second universe extending away from the Big Bang in time.
(Image credit: Meghan McCarter)"It just seems to be the natural, simplest extension of the equations that seem to describe the universe as we see it," he said.
This universe that’s inside the “second cone” is too far down space-time for us to see. Time might seem to run backward there from our reference frame, Learned said. But beings in that universe would still see cause coming before effect, just like we do in ours. Time runs away from the Big Bang in that universe, just like it does in ours. "Away from the Big Bang" in that universe is the opposite direction from the direction of time in our universe. but it doesn't run "backward" in the way we might imagine.
Our universe exists on the other side of that universe's ancient history, and that universe exists on the other side of ours.
See next post for Page 2
