50 minutes ago
https://www.quantamagazine.org/gravity-s...-20260925/
EXCERPTS: But even after covering numerous developments in holography and having countless conversations with the physicists involved, I still felt confused. I had heard that holography suggested that gravity and quantum mechanics are one and the same, and that space might be an illusion. I had also heard holography described both as a mathematical fact and as a speculative flight of fancy. So I tried to triangulate these wild ideas and figure out what, exactly, the holographic principle implies about our universe.
Put a box around any region of space (space-time, really, but I’m going to drop time throughout this essay for ease of visualization, as physicists often do). The holographic principle asserts that no matter what’s going on inside — from gas molecules pinging around to black holes colliding — you can decipher the entire contents of the box just by repeatedly measuring points on the surface.
Pause for a moment to reflect on how outrageous this assertion is. You can’t see into the box at all. Nevertheless, holography says that you can learn exactly what’s happening everywhere in the box without any access to the interior. Observing the surface alone is enough. In this sense, the amount of stuff that fills a box is the same as the amount of paint that covers it. That’s a violation of logic and geometry. It asks us to erase the categorical difference between square meters and cubic meters. It recalls how holographic images appear to have depth despite being flat, except the bird in the hologram is the same as an actual bird.
[...] Why would anyone entertain such a far-fetched notion? It’s rooted in thought experiments and math, and it appears to trace back to one force: “a miracle of gravity,” Czech said.
Scientists have known for more than a century that gravity is different from the other forces. Imagine a box filled with electric charges, representing one of the other fundamental forces, electromagnetism. The stuff in the box consists of the charges and the electric field they create, which also passes through the outer surface. You will have a problem if you try to infer what arrangement of charges generates the field by looking at the surface alone. Because positive charges neutralize negative charges, different arrangements can look the same. If you observe no field, it could mean there’s no charge inside — or it could mean that the effects of the positive charges are perfectly blocking the effects of the negative charges. From the surface, you can’t tell the difference.
Scientists have known for more than a century that gravity is different from the other forces. Imagine a box filled with electric charges, representing one of the other fundamental forces, electromagnetism. The stuff in the box consists of the charges and the electric field they create, which also passes through the outer surface. You will have a problem if you try to infer what arrangement of charges generates the field by looking at the surface alone. Because positive charges neutralize negative charges, different arrangements can look the same. If you observe no field, it could mean there’s no charge inside — or it could mean that the effects of the positive charges are perfectly blocking the effects of the negative charges. From the surface, you can’t tell the difference.
With gravity, mass plays the role of charge. It bends space-time around it, and it is always positive. There is no negative mass, so you can always infer the one real arrangement of stuff inside from the warping of space-time at the surface of your box. “Intuitively, this is why holography is plausible,” said Laurent Freidel, a physicist studying quantum gravity at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.
But holography really starts to bite only after you take the intricate details of quantum mechanics into account... (MORE - missing details)
EXCERPTS: But even after covering numerous developments in holography and having countless conversations with the physicists involved, I still felt confused. I had heard that holography suggested that gravity and quantum mechanics are one and the same, and that space might be an illusion. I had also heard holography described both as a mathematical fact and as a speculative flight of fancy. So I tried to triangulate these wild ideas and figure out what, exactly, the holographic principle implies about our universe.
Put a box around any region of space (space-time, really, but I’m going to drop time throughout this essay for ease of visualization, as physicists often do). The holographic principle asserts that no matter what’s going on inside — from gas molecules pinging around to black holes colliding — you can decipher the entire contents of the box just by repeatedly measuring points on the surface.
Pause for a moment to reflect on how outrageous this assertion is. You can’t see into the box at all. Nevertheless, holography says that you can learn exactly what’s happening everywhere in the box without any access to the interior. Observing the surface alone is enough. In this sense, the amount of stuff that fills a box is the same as the amount of paint that covers it. That’s a violation of logic and geometry. It asks us to erase the categorical difference between square meters and cubic meters. It recalls how holographic images appear to have depth despite being flat, except the bird in the hologram is the same as an actual bird.
[...] Why would anyone entertain such a far-fetched notion? It’s rooted in thought experiments and math, and it appears to trace back to one force: “a miracle of gravity,” Czech said.
Scientists have known for more than a century that gravity is different from the other forces. Imagine a box filled with electric charges, representing one of the other fundamental forces, electromagnetism. The stuff in the box consists of the charges and the electric field they create, which also passes through the outer surface. You will have a problem if you try to infer what arrangement of charges generates the field by looking at the surface alone. Because positive charges neutralize negative charges, different arrangements can look the same. If you observe no field, it could mean there’s no charge inside — or it could mean that the effects of the positive charges are perfectly blocking the effects of the negative charges. From the surface, you can’t tell the difference.
Scientists have known for more than a century that gravity is different from the other forces. Imagine a box filled with electric charges, representing one of the other fundamental forces, electromagnetism. The stuff in the box consists of the charges and the electric field they create, which also passes through the outer surface. You will have a problem if you try to infer what arrangement of charges generates the field by looking at the surface alone. Because positive charges neutralize negative charges, different arrangements can look the same. If you observe no field, it could mean there’s no charge inside — or it could mean that the effects of the positive charges are perfectly blocking the effects of the negative charges. From the surface, you can’t tell the difference.
With gravity, mass plays the role of charge. It bends space-time around it, and it is always positive. There is no negative mass, so you can always infer the one real arrangement of stuff inside from the warping of space-time at the surface of your box. “Intuitively, this is why holography is plausible,” said Laurent Freidel, a physicist studying quantum gravity at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.
But holography really starts to bite only after you take the intricate details of quantum mechanics into account... (MORE - missing details)