快猫短视频

TIME seems to be the most powerful force, an irresistible river carrying us
from birth to death. To most people it is an inescapable part of life, a
fundamental element of the Universe.

But I think that time is an illusion. Physicists struggling to unify quantum
mechanics and Einstein鈥檚 general theory of relativity have found hints that the
Universe is timeless. I believe that this idea should be taken seriously.
Paradoxically, we might be able to explain the mysterious 鈥渁rrow of
time鈥濃�攖he difference between past and future鈥攂y abandoning time. But
to understand how, we need to change radically our ideas of how the Universe
works.

Let鈥檚 start with Newton鈥檚 picture of absolute time. He argued that objects
exist in an immense immobile space, stretching like a block of glass from
infinity to infinity. His time is an invisible river that 鈥渇lows equably without
relation to anything external鈥�. Newton鈥檚 absolute space and time form a
framework that exists at a deeper level than the objects in it.

To see how it works, imagine a universe containing only three particles. To
describe its history in Newton鈥檚 terms, you specify a succession of sets of 10
numbers: one for time and three for the spatial coordinates of each of the three
particles. But this picture is suspect. As the space-time framework is
invisible, how can you determine all the numbers? As far back as 1872, the
Austrian physicist Ernst Mach argued that the Universe should be described
solely in terms of observable things, the separations between its objects.

With that in mind, we can use a very different framework for the
three-particle Universe鈥攁 strange, abstract realm called Triangle Land.
Think of the three particles as the corners of a triangle. This triangle is
completely defined by the lengths of its three sides鈥攋ust three numbers.
You can take these three numbers and use them as coordinates, to mark a point in
an abstract 鈥渃onfiguration space鈥� (see Diagram).

Each possible arrangement of three particles corresponds to a point in this
space. There are geometrical restrictions鈥攏o triangle has one side longer
than the other two put together鈥攕o it turns out that all the points lie in
or on a pyramid. At the apex of Triangle Land, where all three coordinates are
zero, is a point that I call Alpha. It represents the triangle that has sides
all of zero length (in other words, all three particles are in the same
place).

In the same way, the configurations of a four-particle universe form
Tetrahedron Land. It has six dimensions, corresponding to the six separations
between pairs of particles鈥攈ard to conceive, but it exists as a
mathematical entity. And even for the stupendous number of particles that make
up our own Universe, we can envisage a vast multidimensional structure
representing its configurations. In collaboration with Bruno Bertotti of Pavia
University in Italy, I have shown that conventional physics still works in this
strange world. As Plato taught that reality exists as perfect forms, I think of
the patterns of particles as Platonic forms, and call their totality
Platonia.

Platonia is an image of eternity. It is all the arrangements of matter that
can be. Looking at it as a whole, there seems to be no more river of time. But
could time be hiding? Perhaps there is some sort of local time that makes sense
to inhabitants of Platonia.

In classical physics, something like time can indeed creep back in. If you
were to lay out all the instants of an evolving Newtonian universe, it would
look like a path drawn in Platonia. As a godlike being, outside Platonia, you
could run your finger along the path, touching points that correspond to each
different arrangement of matter, and see a universe that continuously changes
from one state to another. Any point on this path still has something that looks
like a definite past and future.

Now鈥檚 the place

But we know that classical physics is wrong. The world is described by
quantum mechanics鈥攁nd in the arena of Platonia, quantum mechanics kills
time.

In the quantum wave theory created by Schr枚dinger, a particle has no
definite position, instead it has a fuzzy probability of being at each possible
position. And for three particles, say, there is a certain probability of their
forming a triangle in a particular orientation with its centre of mass at some
absolute position. The deepest quantum mysteries arise because of holistic
statements of this kind. The probabilities are for the whole, not the parts.

What probabilities could quantum mechanics specify for the complete Universe
that has Platonia as its arena? There cannot be probabilities at different times
because Platonia itself is timeless. There can only be once-and-for-all
probabilities for each possible configuration.

In this picture, there are no definite paths. We are not beings progressing
from one instant to another. Rather, there are many 鈥淣ows鈥� in which a version of
us exists鈥攏ot in any past or future, but scattered in our region of
Platonia.

This may sound like the 鈥渕any worlds鈥� interpretation of quantum mechanics,
published in 1957 by Hugh Everett of Princeton University. But in that scheme
time still exists: history is a path that branches whenever some quantum
decision has to be made. In my picture there are no paths. Each point of
Platonia has a probability, and that鈥檚 the end of the story.

A similar position was reached by much more sophisticated arguments more than
30 years ago. Americans Bryce DeWitt and John Wheeler combined quantum mechanics
and Einstein鈥檚 theory of general relativity to produce an equation that
describes the whole Universe. Put into the equation a configuration of the
Universe, and out comes a probability for that configuration. There is no
mention of time. Admittedly, the Wheeler-DeWitt equation is controversial and
fraught with mathematical difficulties, but if quantum cosmology is anything
like it鈥攊f it is about probabilities鈥攖he timeless picture is
plausible.

So let鈥檚 take seriously the idea of a 鈥減robability mist鈥� that covers the
timeless Platonic landscape. The density of the mist is just the relative
probability of the corresponding configuration being realised, or experienced,
as an instantaneous state of the Universe鈥攁s a Now. If some Nows in
Platonia have much higher probabilities than others, they are the ones that are
actually experienced. This is like ordinary statistical physics: a glass of
water could boil spontaneously, but the probability is so low that we never see
it happen.

All this seems a far cry from the reality of our lives. Where is the history
we read about? Where are our memories? Where is the bustling, changing world of
our experience? Those configurations of the Universe for which the probability
mist has a high density, and so are likely to be experienced, must have within
them an appearance of history鈥攁 set of mutually consistent records that
suggests we have a past. I call these configurations 鈥渢ime capsules鈥�.

Present past

An arbitrary matter distribution, like dots distributed at random, will not
have any meaning. It will not tell a story. Almost all imaginable matter
distributions are of this kind; only the tiniest fraction seem to carry
meaningful information.

One of the most remarkable facts about our Universe is that it does have a
meaningful structure. All the matter we can observe in any way is found to
contain records of a past.

The first scientists to realise this were geologists. Examining the structure
of rocks and fossils, they constructed a long history of the Earth. Modern
cosmology has extended this to a history of the Universe right back to the big
bang.

What is more, we are somehow directly aware of the passing of time, and we
see motion鈥攁 change of position over time. You may feel these are such
powerful sensations that any attempt to deny them is ridiculous. But imagine
yourself frozen in time. You are simply a static arrangement of matter, yet all
your memories and experience are still there, represented by physical patterns
within your brain鈥攑robably as the strengths of the synapse connections
between neurons. Just as the structure of geological strata and fossils seem to
be evidence of a past, our brains contain physical structures consistent with
the appearance of recent and distant events. These structures could surely lead
to the impression of time passing. Even the direct perception of motion could
arise through the presence in the brain of information about several different
positions of the objects we see in motion.

And that is the essence of my proposal. There is no history laid out along a
path, there are only records contained within Nows. This timeless vision may
seem perverse. But it turns out to have one great potential strength: it could
explain the arrow of time.

We are so accustomed to history that we forget how peculiar it is. According
to conventional cosmology, our Universe must have started out in an
extraordinarily special state to give rise to the highly ordered Universe we
find around us, with its arrow of time and records of a past. All matter and
energy must have originated at a single point, and had an almost perfectly
uniform distribution immediately after the big bang.

Hitherto, the only explanation that science has provided is the anthropic
argument: we experience configurations of the Universe that seem to have a
history because only these configurations have the characteristics to produce
beings who can experience anything. I believe that timeless quantum cosmology
provides a far more satisfying explanation.

In Platonia, there are no initial conditions. Only two factors determine
where the probability mist is dense: the form of some equation (like the
Wheeler-DeWitt equation) and the shape of Platonia. And by sheer logical
necessity, Platonia is profoundly asymmetric. Like Triangle Land, it is a
lopsided continent with a special point Alpha corresponding to the configuration
in which every particle is at the same place.

From this singular point, the timeless landscape opens out, flower-like, to
points that represent configurations of the Universe of arbitrary size and
complexity. My conjecture is that the shape of Platonia cannot fail to influence
the distribution of the quantum probability mist. It could funnel the mist onto
time capsules, those meaningful arrangements that seem to contain records of a
past that began at Alpha.

This is, of course, only speculation, but quantum mechanics supports it. In
1929, the British physicist Nevill Mott and Werner Heisenberg from Germany
explained how alpha particles, emitted by radioactive nuclei, form straight
tracks in cloud chambers. Mott pointed out that, quantum mechanically, the
emitted alpha particle is a spherical wave which slowly leaks out of the
nucleus. It is difficult to picture how it is that an outgoing spherical wave
can produce a straight line,鈥� he argued. We think intuitively that it should
ionise atoms at random throughout space.

Mott noted that we think this way because we imagine that quantum processes
take place in ordinary three-dimensional space. In fact, the possible
configurations of the alpha particle and the particles in the detecting chamber
must be regarded as the points of a hugely multidimensional configuration space,
a miniature Platonia, with the position of the radioactive nucleus playing the
role of Alpha.

Ageless creation

When Mott viewed the chamber from this perspective, his equations predicted
the existence of the tracks. The basic fact that quantum mechanics treats
configurations as whole entities leads to track formation. And a track is just a
point in configuration space鈥攂ut one that creates the appearance of a
past, just like our own memories.

There is one more reason to embrace the timeless view. Many theoretical
physicists now recognise that the usual notions of time and space must break
down near the big bang. They find themselves forced to seek a timeless
description of the 鈥渂eginning鈥� of the Universe, even though they use time
elsewhere. It seems more consistent and economical to use an entirely timeless
description.

But for these ideas to be more than speculation, they should have concrete,
measurable results. Fortunately, Stephen Hawking and other theorists have shown
that the Wheeler-DeWitt equation can lead to verifiable predictions. For
example, established physical theories cannot predict a value for the
cosmological constant, which measures the gravitational repulsion of empty
space. But calculations based on the Wheeler-DeWitt equation suggest that it
should have a very small value. It should soon be possible to measure the
cosmological constant, either by taking the brightness of far-off supernovae and
using that to track the expansion of the Universe, or by analysing the shape of
humps and bumps in the cosmic microwave background. And a definitive equation of
quantum cosmology should give us a precise prediction for the value of the
constant. It is a distant prospect, but the nonexistence of time could be
confirmed by experiment.

The notion of time as an invisible framework that contains and constrains the
Universe is not unlike the crystal spheres invented centuries ago to carry the
planets. After the spheres had been shattered by Tycho Brahe鈥檚 observations,
Kepler said: 鈥淲e must philosophise about these things differently.鈥� Much of
modern physics stems from this insight. We need a new notion of time.