The Fabric of the Cosmos: Space, Time, and the Texture of Reality

by Brian Greene

assessing life through the lens of everyday experience is like gazing at a van Gogh through an empty Coke bottle.

space and time have framed thinking since thinking began.

when looked at the right way, the happenings in the universe not only are explicable but predictable.

quantum mechanics describes a reality in which things sometimes hover in a haze of being partly one way and partly another. Things become definite only when a suitable observation forces them to relinquish quantum possibilities and settle on a specific

outcome.

As we don’t see these extra dimensions, superstring theory is telling us that we’ve so far glimpsed but a meager slice of reality.

should we ascribe an independent reality to space, as we do for other, more ordinary material objects like the book you are now holding, or should we think of space as merely a language for describing relationships between ordinary material objects?

That is, the force you feel is proportional to the amount of matter in the universe.

You feel acceleration only when you accelerate relative to the average distribution of other material inhabiting the cosmos.

time had become so enmeshed with space that the reality of one could no longer be pondered separately from the other.

the combined speed of any object’s motion through space and its motion through time is always precisely equal to the speed of light.

speed of light through space. A watch worn by a particle of light would not tick at all.

geometricalshapes of trajectories in spacetime provide the absolute standard that determines whether something is accelerating. Spacetime, not space alone, provides the benchmark.

Since gravity and acceleration are equivalent, Einstein understood that gravity itself must be nothing but warps and curves in the fabric of spacetime.

General relativity provides the choreography for an entwined cosmic dance of space, time, matter, and energy.

the act of measurement is deeply enmeshed in creating the very reality it is measuring.

Uncertainty is built into the wave structure of quantum mechanics and exists whether or not we carry out some clumsy measurement.

Two things can be separated by an enormous amount of space and yet not have a fully independent existence.

But the concept of change has no meaning with respect to a single moment in time.

Time is a subtle subject and we are far from understanding it fully.

All the physical laws that we hold dear fully support what is known as time-reversalsymmetry. This is the statement that if some sequence of events can unfold in one temporal order (cream and coffee mix, eggs break, gas rushes outward) then these events can also unfold in reverse (cream and coffee unmix, eggs unbreak, gas rushes inward).

From any specified moment, the arrow of entropy increase points toward the future and toward the past.

What the second law of thermodynamics entails is that in the formation of order there is generally a more-than-compensating generation of disorder.

Feynman called this the sum over histories approach to quantum mechanics; it shows that a probability wave embodies all possible pasts that could have preceded a given observation,

Quantum mechanics is starkly efficient: it explains what you see but prevents you from seeing the explanation.

the telltale difference between the quantum and the classical notions of probability is that the former is subject to interference and the latter is not.

Instead, for reasons discussed in the next section, the equations of string theory work only in ten spacetime dimensions—nine of space, plus time. String theory demands more dimensions. This is a fundamentally different kind of result, one never before encountered in the history of physics.

if the electromagnetic force is confined to our three-brane, our three space dimensions, it is unable to probe the extra dimensions, regardless of their size. Photons cannot escape our dimensions, enter the extra dimensions, and then travel back to our eyes or equipment allowing us to detect the extra dimensions, even if they were as large as the familiar space dimensions.

and I and everything we’ve ever seen are permanently imprisoned within our three-brane.Taking account of time, everything is trapped within our four-dimensional slice of spacetime.