Physicists Propose a Mirror Universe Where Time Moves in the Opposite Direction

The theory could solve certain stubborn physics questions such as, where’s all the antimatter.

Imagine waking up after death and living out your old age, until you grew young enough to have a career, and hoped someday to go to college. This is what life might be like in the “mirror” universe, the exact opposite of ours. According to two teams of physicists, our universe may have a twin where time moves backward.


Of course, this is all just theoretical. But the theory answers some fundamental questions physics has been wrestling with for quite some time. One is, if the universe during the Big Bang was made of equal parts matter and antimatter, where’s all the antimatter?

Paul Dirac first proposed antimatter in 1928. Since then, physicists have found a wide range of antiparticles. These are present during high energy collisions in other places in the universe and also within particle accelerators, such as the large hadron collider at CERN.

In a 1964 experiment, which won them the Nobel Prize 16 years later, James Cronin and Val Fitch proved that you cannot have an antimatter universe for the simple reason that the weak nuclear force violates this model. For a while that was that.

Then in 2004, two scientists at Caltech, Professor Sean Carroll and his graduate student Jennifer Chen, revived the mirror universe theory, by trying to address another fundamental physics question, why does time only move in one direction?

Experiments at the HLC at CERN have shown antimatter. But it’s eerily absent in nature. Getty Images.

Through the course of their investigation, they ended up creating a model of the Big Bang which shoots outward in two opposite directions. In our universe, everything is made up of matter, while in the mirror universe, its antimatter.

As time moves forward in one direction in one universe, it moves backward in the other. But from the mirror universe, time would appear to be moving backwards in ours, which begs the question, who is actually in the backwards universe, us or them?   

Generally speaking, when we talk about time, we consider the Second Law of Thermodynamics and in particular, entropy. This is the amount of disorder in a system which will eventually break it down, be it an engine, a computer, a star, or the human body. Entropy grows exponentially until sooner or later, it consumes the entire system. But instead of entropy, Carroll and Chen decided to focus on gravity.

Looking at just 1,000 particles and employing Newtonian physics, they were able to prove that this dual universe theory is possible. Their model even accounts for the weak nuclear force. Two teams of scientists have looked more deeply into this, since.

Physicists have long wondered why the universe only travels in one direction. NASA.

In 2014, one group published their findings in the journal Physical Review Letters. Three scientists collaborated on the project, Julian Barbour of Oxford, Tim Koslowski from the University of New Brunswick, and Flavio Mercati of the Perimeter Institute for Theoretical Physics. They studied a similar, self-contained, 1,000 particle system, based on gravity rather than thermodynamics.

This model showed gravity expanding in two directions, out from what’s been termed the “Janus point,” named after the two-headed Roman god. Here, entropy is how we experience time, as an ever forward motion, known in physics as the “arrow of time.” According to Barbour, if you take time as a natural phenomenon, rather than a pre-existing force, it flows in two different directions, which he contends popped up in their computer model, spontaneously.

As a result, those beings in the mirror cosmos would experience their lives as we do, but subtle differences could cause things to end up radically differently than they do in our epoch. So could you ever step into the mirror universe, should it exist? According to Mercati, no. The two epochs flow out forever from this central point and beings in one universe would never be aware of the other.

Even if there is a mirror universe, you’d never be able to cross the Janus point. Getty Images.

Dr. Carroll has built upon his theory since his groundbreaking announcement. Today, he’s at the California Institute of Technology. Carroll has teamed up with a colleague at MIT, Alan Guth. The model now is more refined, Carroll and Guth claim.

It doesn’t rely on gravity, for one thing. It works based on thermodynamics alone. It even operates smoothly when accounting for particles traveling through infinite space, rather than a self-contained system.

“We call it the two-headed arrow of time,” Guth told New Scientist, “Because the laws of physics are invariant, we see exactly the same thing in the other direction.” In this view, our universe and its mirror, may have been born out of a parent universe.

Their results haven’t been published, yet. One problem is that the model is only proven to work in terms of classical physics. Whether it’ll square with quantum mechanics or even general relativity, no one knows. Yet another issue is that it doesn’t incorporate a fundamental force of the universe, gravity. Researchers aren’t even sure of the exact structure their proposing.

“Instead of having two streams emanating from a river, it could be more like a fountain where you have lots of pairs of springs,” Carroll said. “Or just a whole host of springs flowing out of a fountain in different directions.” Perhaps our epoch is really a part of a much larger multiverse with each separate universe having its own mirror opposite, a fascinating prospect to consider.

To learn more about this theory, click here: 

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New fossils suggest human ancestors evolved in Europe, not Africa

Experts argue the jaws of an ancient European ape reveal a key human ancestor.

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  • The jaw bones of an 8-million-year-old ape were discovered at Nikiti, Greece, in the '90s.
  • Researchers speculate it could be a previously unknown species and one of humanity's earliest evolutionary ancestors.
  • These fossils may change how we view the evolution of our species.

Homo sapiens have been on earth for 200,000 years — give or take a few ten-thousand-year stretches. Much of that time is shrouded in the fog of prehistory. What we do know has been pieced together by deciphering the fossil record through the principles of evolutionary theory. Yet new discoveries contain the potential to refashion that knowledge and lead scientists to new, previously unconsidered conclusions.

A set of 8-million-year-old teeth may have done just that. Researchers recently inspected the upper and lower jaw of an ancient European ape. Their conclusions suggest that humanity's forebearers may have arisen in Europe before migrating to Africa, potentially upending a scientific consensus that has stood since Darwin's day.

Rethinking humanity's origin story

The frontispiece of Thomas Huxley's Evidence as to Man's Place in Nature (1863) sketched by natural history artist Benjamin Waterhouse Hawkins. (Photo: Wikimedia Commons)

As reported in New Scientist, the 8- to 9-million-year-old hominin jaw bones were found at Nikiti, northern Greece, in the '90s. Scientists originally pegged the chompers as belonging to a member of Ouranopithecus, an genus of extinct Eurasian ape.

David Begun, an anthropologist at the University of Toronto, and his team recently reexamined the jaw bones. They argue that the original identification was incorrect. Based on the fossil's hominin-like canines and premolar roots, they identify that the ape belongs to a previously unknown proto-hominin.

The researchers hypothesize that these proto-hominins were the evolutionary ancestors of another European great ape Graecopithecus, which the same team tentatively identified as an early hominin in 2017. Graecopithecus lived in south-east Europe 7.2 million years ago. If the premise is correct, these hominins would have migrated to Africa 7 million years ago, after undergoing much of their evolutionary development in Europe.

Begun points out that south-east Europe was once occupied by the ancestors of animals like the giraffe and rhino, too. "It's widely agreed that this was the found fauna of most of what we see in Africa today," he told New Scientists. "If the antelopes and giraffes could get into Africa 7 million years ago, why not the apes?"

He recently outlined this idea at a conference of the American Association of Physical Anthropologists.

It's worth noting that Begun has made similar hypotheses before. Writing for the Journal of Human Evolution in 2002, Begun and Elmar Heizmann of the Natural history Museum of Stuttgart discussed a great ape fossil found in Germany that they argued could be the ancestor (broadly speaking) of all living great apes and humans.

"Found in Germany 20 years ago, this specimen is about 16.5 million years old, some 1.5 million years older than similar species from East Africa," Begun said in a statement then. "It suggests that the great ape and human lineage first appeared in Eurasia and not Africa."

Migrating out of Africa

In the Descent of Man, Charles Darwin proposed that hominins descended out of Africa. Considering the relatively few fossils available at the time, it is a testament to Darwin's astuteness that his hypothesis remains the leading theory.

Since Darwin's time, we have unearthed many more fossils and discovered new evidence in genetics. As such, our African-origin story has undergone many updates and revisions since 1871. Today, it has splintered into two theories: the "out of Africa" theory and the "multi-regional" theory.

The out of Africa theory suggests that the cradle of all humanity was Africa. Homo sapiens evolved exclusively and recently on that continent. At some point in prehistory, our ancestors migrated from Africa to Eurasia and replaced other subspecies of the genus Homo, such as Neanderthals. This is the dominant theory among scientists, and current evidence seems to support it best — though, say that in some circles and be prepared for a late-night debate that goes well past last call.

The multi-regional theory suggests that humans evolved in parallel across various regions. According to this model, the hominins Homo erectus left Africa to settle across Eurasia and (maybe) Australia. These disparate populations eventually evolved into modern humans thanks to a helping dollop of gene flow.

Of course, there are the broad strokes of very nuanced models, and we're leaving a lot of discussion out. There is, for example, a debate as to whether African Homo erectus fossils should be considered alongside Asian ones or should be labeled as a different subspecies, Homo ergaster.

Proponents of the out-of-Africa model aren't sure whether non-African humans descended from a single migration out of Africa or at least two major waves of migration followed by a lot of interbreeding.

Did we head east or south of Eden?

Not all anthropologists agree with Begun and his team's conclusions. As noted by New Scientist, it is possible that the Nikiti ape is not related to hominins at all. It may have evolved similar features independently, developing teeth to eat similar foods or chew in a similar manner as early hominins.

Ultimately, Nikiti ape alone doesn't offer enough evidence to upend the out of Africa model, which is supported by a more robust fossil record and DNA evidence. But additional evidence may be uncovered to lend further credence to Begun's hypothesis or lead us to yet unconsidered ideas about humanity's evolution.