The bottom line is that time travel is allowed by the laws of physics.
The melded nature of space and time is intimately woven with properties of light speed. The inviolable nature of the speed of light is actually, in Einstein’s hands, talking about the inviolable nature of cause and effect.
The central idea of string theory is quite straightforward. If you examine any piece of matter ever more finely, at first you’ll find molecules, atoms, sub-atomic particles. Probe the smaller particles, you’ll find something else, a tiny vibrating filament of energy, a little tiny vibrating string.
The absolute worst thing that you ever can do, in my opinion, in bringing science to the general public, is be condescending or judgmental. It is so opposite to the way science needs to be brought forth.
Supersymmetry is a theory which stipulates that for every known particle there should be a partner particle. For instance, the electron should be paired with a supersymmetric ‘selectron,’ quarks ought to have ‘squark’ partners, and so on.
For most people, the major hurdle in grasping modern insights into the nature of the universe is that these developments are usually phrased using mathematics.
When you realize that quantum mechanics underlies all physical processes, from the fusing of atoms in the sun to the neural firings that constitutes the stuff of thought, the far-reaching implications of the proposal become apparent. It says that there’s no such thing as a road untraveled. Yet each such road – each reality – is hidden from all others.
A tree is to the entire universe as a string is to an atom.
Quantum mechanics challenges this view by revealing, at least in certain circumstances, a capacity to transcend space; long-range quantum connections can bypass spatial separation. Two objects can be far apart in space, but as far as quantum mechanics is concerned, it’s as if they’re a single entity.
Extraordinary emblems of math’s ability to illuminate the dark corners of the cosmos, black holes have become the cynosures of modern physics.
According to string theory, if we could examine these particles with even greater precision – a precision many orders of magnitude beyond our present technological capacity – we would find that each is not pointlike, but instead consists of a tiny one-dimensional loop. Like an infinitely thin rubber band, each particle contains a vibrating, oscillating, dancing filament that physicists, lacking Gell-Mann’s literary flair, have named a string.
We revere the absolute but are bound to the transitory.
Just as important, the energy released by the inflaton field isn’t lost-instead, like a cooling vat of steam condensing into water droplets, the inflaton’s energy condenses into a uniform bath of particles that fill space. This two-step process-brief but rapid expansion, followed by energy conversion to particles-results in a huge, uniform spatial expanse that’s filled with the raw material of familiar structures like stars and galaxies.
General relativity then establishes that objects move toward regions where time elapses more slowly; in a sense, all objects “want” to age as slowly as possible. From an Einsteinian perspective, that explains why an object falls when you let go of it.
Stephen Hawking showed mathematically that the entropy of a black hole equals the number of Planck-sized cells that it takes to cover its event horizon. It’s as if each cell carries one bit, one basic unit of information.
And since, according to the big bang theory, the bang is what is supposed to have happened at the beginning, the big bang leaves out the bang. It tells us nothing about what banged, why it banged, how it banged, or, frankly, whether it ever really banged at all.
If you were to head out into the cosmos, traveling ever farther, would you find that space goes on indefinitely, or that it abruptly ends?
A stack of five off-the-shelf terabyte hard drives fits comfortably within a sphere of radius 50 centimeters, whose surface is covered by about 1070 Planck cells. The surface’s storage capacity is thus about 1070 bits, which is about a billion, trillion, trillion, trillion, trillion terabytes, and so enormously exceeds anything you can buy. No one in Silicon Valley cares much about these theoretical constraints.
The skyscraper is but a physical realization of the information contained in the architect’s design.
Much as Hamlet famously declares, “I could be bounded in a nutshell, and count myself a king of infinite space,” each of the bubble universes appears to have finite spatial extent when examined from the outside, but infinite spatial extent when examined from the inside. And that’s a marvelous realization.
The point being that everything emerges from the same collection of ingredients governed by the same physical principles. And those principles, as attested to by a few hundred years of observation, experimentation, and theorizing, will likely be expressed by a handful of symbols arranged in a small collection of mathematical equations. That is an elegant universe.