Democritus and the title of Thomas Friedman's bestseller might have gotten it right after all. But it's the universe, not the Earth, that might be flat – a 2-dimensional hologram, according to an international team of researchers.
Holograms might be most familiar as the colorful 3-D images used as security measures on some credit cards and currencies. But of course, they're not really 3-dimensional, are they? They contain all the information necessary for our eyes to perceive them that way, but the pictures are actually printed on a 2-D surface. A new calculation, published last Monday in Physical Review Letters, says that models describing our early universe similarly have now been shown to agree with recent observations just as well as standard 3-D models do.
The sticking point is gravity. Ever since Einstein's General Theory of Relativity described the force that keeps our feet on the ground as a consequence of the shape of space, it's been giving physicists headaches.
Other forces, including electromagnetism, can be explained in terms of particles. Magnets may seem to be magically tugging on each other from a distance, but at some level they're swapping photons. Gravity has vigorously resisted this kind of particle-level description, giving rise to exotic theories of quantum gravity such as string theory.
One proposed bridge between these odd theories of gravity and more established quantum theories of particles accomplishes "lots of wonderful things," writes particle physicist Raphael Bousso of the University of California at Berkeley in an email to The Christian Science Monitor.
"One of them is that it makes the holographic principle manifest," he writes.
As he explains it, the recent paper, which he was not involved with, borrows some tools from this theoretical bridge, and applies them to the early moments after the Big Bang.
In the universe's first moments, it was expanding so rapidly that the standard bag of tricks may not apply, if their assumptions hold true.
Light emitted during this expansion still exists today, but it has been distorted by the expanding universe. Light waves that once spanned nanometers (less than one-ten-thousandth the diameter of a strand of hair) have had their wavelengths stretched a thousand times longer, into the micrometer range, where we can detect them as the cosmic microwave background – omnipresent radiation that contributes to the snowy static seen on an untuned television.
Those distortions of the Big Bang's afterglow still contain hints as to what the early universe was like, including whatever exotic physics might have been going on in the very beginning, so it's of great interest to physicists. The European Space Agency's Planck satellite, whose mission ended in 2013, provided the most detailed observations to date.
Scientists have continued to analyze data from the Planck satellite, and in this new paper, researchers argue that their holographic model of the universe was "consistent with cosmic inflation," lead author Niayesh Afshordi of Waterloo University and the Perimeter Institute for Theoretical Physics tells the Monitor in a phone interview – or at least as consistent as the more popular 3-dimensional model.
Future data sets may tell a different story, but for now there isn't enough information to suggest one model over another. If their theory proves correct, it could imply that one of the dimensions we experience is "extra," like depth in a hologram. It isn't "really" there in some sense, but rather emerges from our perception of a more fundamental, flat structure.
"Imagine that everything you see, feel, and hear in three dimensions (and your perception of time) in fact emanates from a flat two-dimensional field. The idea is similar to that of ordinary holograms where a three-dimensional image is encoded in a two-dimensional surface, such as in the hologram on a credit card. However, this time, the entire universe is encoded," explained Professor of Mathematical Sciences Kostas Skenderis at the University of Southampton in a press release.
Of the team's approach, Dr. Bousso says that adapting "some mathematical ingredients" of a quantum gravity framework to fit our early universe "may or may not be the right thing to do," but emphasizes that even if it isn't, that would only mean the universe is not the particular kind of hologram they propose.
The word "holographic" gets tossed around in science fiction, but the general "holographic principle" has nothing to do with Star Trek, or the idea that our universe is actually a computer simulation, and is quite well established.
"We already know that the universe is a hologram," Bousso says. "It applies not only to the observed universe but to [your] room, the interior of a black hole, and any other realistic situation we can imagine."
He refers to the surprising fact that information capacity depends on the flat surface area surrounding a volume, rather than the volume itself. Put another way, doubling the side length of a cube only increases the maximum information inside by 4, rather than the logical 8.
Say you're allowed to bring a notecard of information into an exam with you. Wanting to maximize your advantage, you'd logically use a sharp pencil and write as small as possible. Even better, if the rule specified only the size of your learning aid, you could bring an SD card loaded with digital textbooks instead. In daily life, how much information we can store depends heavily on the medium we use to store it.
But the holographic principle establishes a natural limit to our information packing games. Eventually, if we cram enough SD cards into our exam room, the pile will collapse under its own weight and form a black hole. Calculating this limit – the maximum amount of information you can gather in one place – turns out to depend not on the volume of the room, as one might logically expect, but somehow the surface area of the classroom.
Even more shocking, that calculation makes no assumptions about what's inside the classroom or what the ultimate nature of reality is: atoms, quarks, or superstrings. It's medium-agnostic.
The principle has proven true for every situation in which it's been tested, but no one knows why. "It's a very overarching, mysterious pattern that I don't think we've even scratched the surface of," Bousso said in a 2006 lecture.
Any unifying theory of physics should explain the underlying reason for it.
"Once we have a proper quantum theory of gravity, it will make this pattern seem perfectly obvious," he continued.
This baffling concept of being able to capture all the information of a 3-D volume with only its flat surface lies at the heart of the holographic principle, and its ability to sidestep sticky issues like what exactly is inside the box makes it a valuable tool for physicists trying to probe inaccessible areas of the universe.
In the case of the early universe, both our theories of gravity and quantum particles run into problems, but as Dr. Afshordi puts it, the "holographic principle really gives us a way to get around that, even if you have no idea what the theory of quantum gravity is."
He takes a humble, philosophical view of his team's efforts to apply the mathematics of holography to the unknowable early moments of the cosmos.
“We’re just applying holography to cosmology,” he says. "Holography is really a tool. What is real, and what is not, is up to you."
[Editor's note: An earlier version of this story incorrectly implied that Christopher Columbus believed the Earth was flat.]