---------------------- 2707 - SPACETIME - still a conundrum in science?
-
- Is the nature of reality revealed by the laws of quantum mechanics? According to the quantum theory, before the observation is made, a subatomic particle exists in several states, called a superposition. Once the particle is observed, it instantaneously collapses into a single position.
-
- These known elementary particles are codified in a 40-year-old set of equations called the “Standard Model” They still lack a sensible pattern and seem astonishingly fine-tuned for life. But do they obey the laws of superposition?
-
- Einstein’s general theory of relativity beautifully weaves space and time together into a four-dimensional fabric, known as space-time, and equates gravity with warps in that fabric.
-
- But, Einstein’s theory and the space-time concept break down inside black holes and at the moment of the big bang. Space-time may be a translation of some other description of “reality’ that, though more abstract or unfamiliar, can have greater explanatory power. Our challenge is to discover it.
-
- Ever since Einstein, scientists have also been scratching their heads about how to make sense of space and time. Before then, almost everybody thought Isaac Newton had figured it all out. Time flows equably without relation to anything external. Absolute space is also always similar and immovable.
-
- But Einstein’s theories turned Newton’s absolute space and time into a relativistic mash-up. His equations suggested a merged space-time, a new sort of arena in which the players altered the space of the playing field. It was a physics game changer.
-
- No longer did space and time provide a featureless backdrop for matter and energy. Formerly independent and uniform, space and time became inseparable and variable. And as Einstein showed in his general theory of relativity, matter and energy warped the space-time surrounding them.
-
- That simple truth explained gravity. Newton’s apparent force of attraction became an illusion perpetrated by space-time geometry. It was the shape of space-time that dictated the motion of massive bodies, a symmetry, since massive bodies determined space-time’s shape.
-
- Verification of Einstein’s space-time revolution came a century ago, when an eclipse expedition confirmed his general theory’s prime prediction, a precise amount of bending of light passing near the edge of a massive body, in this case the Sun.
-
- Space-time has remained mysterious, since it was something rather than nothing, it was natural to wonder where it came from.
-
- Now a new revolution is on the verge of answering that question, based on insights from the other great physics surprise of the last century: “quantum mechanics“. Today’s revolution offers the potential for yet another rewrite of space-time theories, with the bonus of perhaps explaining why quantum mechanics seems so weird.
-
- Space-time and gravity must ultimately emerge from something else. Otherwise it’s hard to see how Einstein’s gravity and the math of quantum mechanics can reconcile their longstanding incompatibility.
-
- Einstein’s view of gravity as the manifestation of space-time geometry has been enormously successful. But so also has been quantum mechanics, which describes the machinations of matter and energy on the atomic scale with unerring accuracy. Attempts to find coherent math that accommodates quantum weirdness with geometric gravity have met formidable technical and conceptual roadblocks.
-
- At least that has long been so for attempts to understand ordinary space-time. But clues to a possible path to progress have emerged from the theoretical study of alternate space-time geometries with unusual properties.
-
- One such alternate, known as “anti de Sitter space“, is weirdly curved and tends to collapse on itself, rather than expanding as the universe we live in does. As a laboratory for studying theories of quantum gravity, it has a lot to offer.
-
- Studies of anti de Sitter space suggest that the math describing gravity ( space-time geometry) can be equivalent to the math of quantum physics in a space of one less dimension.
-
- Think of a hologram, a flat, two-dimensional surface that incorporates a three-dimensional image. In a similar way, perhaps the four-dimensional geometry of space-time could be encoded in the math of quantum physics operating in three-dimensions.
-
- “Entanglement” is a spooky connection linking particles separated even by great distances. If emitted from a common source, such particles remain entangled no matter how far they fly away from each other. If you measure a property (such as spin or polarization) for one of them, you then know what the result of the same measurement would be for the other.
-
- Before the measurement, those properties are not already determined, as a counterintuitive fact verified by many experiments. It seems like the measurement at one place determines what the measurement will be at another distant location.
-
- That sounds like entangled particles must be able to communicate faster than light. Otherwise it’s impossible to imagine how one of them could know what was happening to the other across a vast space-time expanse.
-
- But they actually don’t send any message at all. So how do entangled particles transcend the space-time gulf separating them? Perhaps the answer is they don’t have to because entanglement doesn’t happen in space-time. Entanglement creates space-time.
-
- The emergence of space-time and gravity is a mysterious phenomenon of quantum many-body physics that we would like to understand. Vigorous effort by several physicists has produced theoretical evidence that networks of entangled quantum states weave the space-time fabric.
-
- These quantum states are often described as “qubits” , bits of quantum information (like ordinary computer bits, but existing in a mix of 1 and 0, not simply either 1 or 0). Entangled qubits create networks with geometry in space with an extra dimension beyond the number of dimensions that the qubits live in.
-
- So the quantum physics of qubits can then be equated to the geometry of a space with an extra dimension. Best of all, the geometry created by the entangled qubits may very well obey the equations from Einstein’s general relativity that describe motion due to gravity.
-
- Apparently, a geometry with the right properties built from entanglement has to obey the gravitational equations of motion.
-
- Nobody really knows exactly what quantum processes in the real world would be responsible for weaving space-time’s fabric. Maybe some of the assumptions made in calculations so far will turn out to be faulty. But it could be that physics is on the brink of peering more deeply into nature’s foundations than ever before, into an existence containing previously unknown dimensions of space and time (or sight and sound) that might end up
-
- May you live in interesting times. It has been 100 years since spacetime and relativity were proposed. We are due for another great discovery. Dark Energy, Dark Matter, spacetime are all mysteries that our next generation needs to solve.
-
- We are but wanderers on the beach picking up pebbles of knowledge with a whole ocean of the unknown before us. May you live in interesting times.
-
- April 14, 2020 2707
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Wednesday, April 15, 2020 -------------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment