Saturday, January 19, 2013
Big Question: Does quantum foam hold the keys to time travel?
Forward to the past? Backward to the future? Sure, it happens in the movies, but could real-world physics tell us anything about the possibility of human time travel in the near future?
Curiosity contributor Susan Sherwood examined the mind-blowing possibilities of time travel via quantum foam and came up with the following answer.
Time travel through wormholes is theoretically possible under the known laws of physics, and quantum foam may be one piece of that puzzle. What is this foam? How could it work? We have to delve into the tiny world of quantum mechanics for some answers.
The basic laws of Newtonian physics cover what we can see every day with our eyes: If you let go of a book, it will fall; push a ball and it will roll. Quantum mechanics concerns the tiniest, unseen parts of the world, parts even smaller than subatomic particles. Measuring things on that scale is tricky, and the smallest measurement used by physicists is the Planck length, written as a one preceded by 34 zeros and a decimal point. This is the size of the smallest particles that compose the fabric of space-time [source: Johnson].
At this miniscule scale, it is theorized that tiny particles or black holes are fluctuating -- appearing and disappearing. This churning mix of particles is called quantum foam. To visualize it, imagine a swimming pool full of boiling water. Up close, you can see frothing and bubbles bursting, but if you viewed a satellite photo of the pool, the surface would appear unbroken. That's a comparison between what might be happening at the subatomic level and what we see with our eyes according to the theory of quantum foam.
What does this have to do with wormholes? It is within quantum foam that wormholes are theoretically believed to exist. They can move in and out of existence, connecting different places and times. Since they are so incredibly small, humans couldn't use them for time travel. Some theoretical physicists, though, are exploring the concept of a wormhole time machine -- the idea being that a wormhole might be ensnared and expanded until it could become a transit for time travelers [source: Hawking].
This is still in the hypothetical stages, of course. However, a scientist at the University of Maryland believes he can create a substance in a laboratory that mimics quantum foam [source: Technology Review]. This kind of study may help move quantum foam from a theoretical entity to a known quantity. Would H. G. Wells' Time Machine (1895) then be far behind?
What is 'quantum foa
This is an idea that was
originally proposed by Nobel physicist John Wheeler back in the early
1960's to describe what space-time 'looks like' at scales of 10^-33
centimeters.
The basic idea is that gravity is a field with many of the same fundamental properties as the other fundamental 'force' fields in Nature. This means that the state of this field is, at some level, uncertain and described by quantum mechanics. Since Einstein's general theory of relativity requires that gravitational fields and space-time be one and the same mathematical objects, this means that space-time itself is also subject to the kinds of uncertainty required by quantum systems. This indeterminacy means that you cannot know with infinite precision BOTH the geometry of space-time, and the rate of change of the space-time geometry, in direct analogy with Heisenberg's Uncertainty Principle for quantum systems.
Wheeler imagined that this indeterminacy for space-time required that at the so-called Planck Scale of 10^-33 centimeters and 10^-43 seconds, space-time has a foaminess to it with sudden changes in its geometry into a wealth of complex shapes and textures. You would have quantum black holes appear at 10^-33 centimeters, then evaporate in 10^-43 seconds. Wormholes would form and dissolve, and later theorists even postulated 'baby universe' production could happen under these conditions.
The problem is that we have no evidence that 1) gravity is a quantum field and 2) that space-time has this type of structure at these scale
The basic idea is that gravity is a field with many of the same fundamental properties as the other fundamental 'force' fields in Nature. This means that the state of this field is, at some level, uncertain and described by quantum mechanics. Since Einstein's general theory of relativity requires that gravitational fields and space-time be one and the same mathematical objects, this means that space-time itself is also subject to the kinds of uncertainty required by quantum systems. This indeterminacy means that you cannot know with infinite precision BOTH the geometry of space-time, and the rate of change of the space-time geometry, in direct analogy with Heisenberg's Uncertainty Principle for quantum systems.
Wheeler imagined that this indeterminacy for space-time required that at the so-called Planck Scale of 10^-33 centimeters and 10^-43 seconds, space-time has a foaminess to it with sudden changes in its geometry into a wealth of complex shapes and textures. You would have quantum black holes appear at 10^-33 centimeters, then evaporate in 10^-43 seconds. Wormholes would form and dissolve, and later theorists even postulated 'baby universe' production could happen under these conditions.
The problem is that we have no evidence that 1) gravity is a quantum field and 2) that space-time has this type of structure at these scale
Friday, January 4, 2013
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