Warp speed: How the outer edges of the universe travel faster than the speed of light
The answer can give us an indication of where our universe is headed and how it might end.
As children it’s driven into us in early science classes as a cardinal rule: nothing can travel faster than light. But at least one thing is thought to, or at least appears to be—the fundamental material of the universe itself. Astronomers believe there are galaxies moving away from ours at a rate faster than light speed. As a result, we’ll likely never get to see them.
13.78 billion years ago, the solidarity exploded in an event we call the Big Bang. This was a point in the universe of infinite density and heat. After the explosion, the universe expanded at the rate of 10¹⁶ in a fraction of a second, during a period of inflation that occurred at a velocity faster than the speed of light. After that, you’d think that the universe would expand at a constant rate or even slow down. If it had slowed down, we’d be able to see right to the edge as there wouldn’t be anywhere that would be too far for light to travel.
Instead, the rate of universal expansion has been speeding up. And there are places in the universe that are so far away, photons will never make it there. As a result, the edges of our cosmos remain in shadow. What lies beyond is an intrepid mystery we might not ever solve.
Expansion still occurs today, quizzically, at an ever-increasing rate. Note that it isn’t just matter but the fabric of the universe itself, as the matter in a way rides atop of it. What’s more, the galaxies farther away appear to be moving faster than those closer to us. There may even be ones close by that are moving faster than light. If there are, we’ll find them difficult to detect.
Timeline of the expansion of the universe since the Big Bang. Credit: NASA/WMAP Science Team.
Galaxies and other matter are like sesame seeds resting atop a piece of dough, with the dough standing in for the fabric of the universe. When we place the dough in an oven it expands, and those seeds on the outside rim appear as if they expand out faster than those near the middle. The same may be true of the universe.
The rate of universal expansion is 68 kilometers per second per megaparsec. A parsec is 3.26 million light-years, while a megaparsec is a million parsecs. For every parsec away a galaxy is from ours, you add 68 km/s to its velocity.
Once we get out to about 4,200 megaparsecs away, galaxies travel faster than light. Just to boggle your mind, consider that 4,200 megaparsecs = 130,000,000,000,000,000,000,000 km. Astronomers can calculate how far away a galaxy is by the distance it’s gone and the time it takes to travel that distance, all by carefully observing the light coming from it.
We can tell how far away a galaxy is by something called red shift and blue shift. As a galaxy moves away, the light from it takes longer to reach us. All that space between the galaxy and us forces the wavelength of the light to elongate, moving it toward the red part of the spectrum. This is known as red shift. Those objects moving away from us appear red while those moving toward us, whose wavelengths shorten, appear blue.
Panoramic view of the entire near-infrared sky. This image shows how the galaxies beyond are own located. The image was taken by the 2MASS Extended Source Catalog (XSC). This contains over 1.5 million galaxies and half a billion stars. The galaxies are coded by redshift, indicated by the numbers in parentheses). Credit: Thomas Jarrett, IPAC/Caltech.
The furthest thing out there that we can detect is the cosmic microwave background (CMB). This is the light residue left over from the Big Bang. Created 13.7 billion years ago, it now stretches out homogenously 46 billion light-years away in every direction.
According to Paul Sutter, Ohio State University astrophysicist and COSI Science Center Chief Scientist, the notion that the speed of light is the topmost speed for matter (or information), comes from Einstein’s special relativity. But this is part of what he calls “local physics.” It can and in fact must be applied to things nearby.
Far out in the deepest reaches of space, however, general relativity applies, but special relativity may not and with it, the speed of light as the topmost velocity becomes less certain. So what are the implications of an ever-accelerating universe? Nothing short of a cosmic heat death. Over billions of years, galaxies are thought to expand so far out from each other that the gases that congregate to form stars won’t be able to get together. They’ll be spread too thin.
Light from other galaxies won’t be able to reach us, either. And with no new stars forming, they’ll be none to replace those that have burned out. That means a slow fading of all light in the universe, and in its place, a cosmos forever shrouded in frozen darkness. That’s of course unless other forces can counteract this phenomenon.
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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.
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