It’s still possible we all live inside a hologram

Is our universe actually just a hologram? This idea has been floated around before, and isn’t just some trippy, somewhat horrifying thought one gets at 3am, perhaps along with (or as a result of) insomnia. Instead, it could very well be an actual physical property of the universe. And it may have been under our noses all this time.

Mathematicians are already familiar with the holographic principle, which the famous physicist Leonard Susskind first proposed. It asserts that a volume of space can be thought of as encoded on a boundary to it — such as an observer-dependent gravitational horizon — and therefore needs one less dimension than it appears to need. By extension, since our universe seems three-dimensional to us, it could actually be a two-dimensional structure that’s overlaid onto an incredibly large cosmic horizon.

Back in 1997, Juan Maldacena first postulated the theory of a holographic universe, saying that gravity arises from thin, vibrating strings that exist in 10 dimensions. Other physicists have been working with the concept since.

“The work culminated in the last decade, and it suggests, remarkably, that all we experience is nothing but a holographic projection of processes taking place on some distant surface that surrounds us,” wrote physicist Brian Greene, from Columbia University, in 2011. “You can pinch yourself, and what you feel will be real, but it mirrors a parallel process taking place in a different, distant reality.”

Now physicists at TU Wien (Vienna) are proposing that the holographic principle works even in a flat spacetime, and not just in theoretical regions with negative curvature. As a general rule, gravitational phenomena are described with three spatial dimensions, while quantum particles are described with just two dimensions. It turns out that you can map the results of one onto the other — a stunning finding that has led to over 10,000 scientific papers in theoretical physics on negatively curved spaces thus far. But it hasn’t seemed at all related to our own, flat, positively curved universe until now.

Black hole spin
“If quantum gravity in a flat space allows for a holographic description by a standard quantum theory, then there must by physical quantities, which can be calculated in both theories – and the results must agree,” said Daniel Grumiller of TU Wien in a statement. That includes the appearance of quantum entanglement in the gravitational theory, meaning that the particles can’t be described individually. It turns out you can measure the amount of entanglement in a quantum system, which is called the entropy of entanglement. Grumiller shows that it has the same value in flat quantum gravity and in a low-dimension quantum field theory.

“This calculation affirms our assumption that the holographic principle can also be realized in flat spaces. It is evidence for the validity of this correspondence in our universe,” says Max Riegler, also of TU Wien. “The fact that we can even talk about quantum information and entropy of entanglement in a theory of gravity is astounding in itself, and would hardly have been imaginable only a few years back. That we are now able to use this as a tool to test the validity of the holographic principle, and that this test works out, is quite remarkable,” said Grumiller.

That does sound incredible. But unfortunately, this brings us one step closer to the terrifying reality that maybe we are living in a hologram.

Source: It’s still possible we all live inside a hologram | ExtremeTech


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