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TOPIC: Arrow of Time


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Could multiple universes explain our arrow of time? Does time run backwards in other universes?

We travel through life from womb to tomb, not vice-versa, yet physicists have no real explanation for why time flows in only one direction. The microscopic laws that underlie the behaviour of particles have no such arrow, working equally well backwards as forwards. So why doesn't time run backwards?
Physicists usually explain the arrow of time using the concept of increasing entropy - a measure of the disorder of a system. The universe evolves from a highly-ordered, low-entropy beginning, to a progressively more disordered state, defining time's arrow. So, sugar cubes dropped into coffee dissolve as time passes, increasing the disorder of the coffee-sugar system; but they do not re-solidify. To Mersini-Houghton, a physicist at the University of North Carolina, Chapel Hill, however, this reasoning simply begs the following question: Why did the universe begin in a highly unlikely low-entropy state in the first place?

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Ed ~ The Arrow of time is dictated by the boundary conditions of this universe, it does not require multiple universes explain the arrow of time.
The universe started at a low-entropy state because, according to R Penrose et al., an ultimately expanding universe resets spacetime.


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Is Time an Illusion?

* Time is an especially hot topic right now in physics. The search for a unified theory is forcing physicists to reexamine very basic assumptions, and few things are more basic than time.
* Some physicists argue that there is no such thing as time. Others think time ought to be promoted rather than demoted. In between these two positions is the fascinating idea that time exists but is not fundamental. A static world somehow gives rise to the time we perceive.
* Philosophers have debated such ideas since before the time of Socrates, but physicists are now making them concrete. According to one, time may arise from the way that the universe is partitioned; what we perceive as time reflects the relations among its pieces.

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Caltech theoretical physicist Sean Carroll's book "From Eternity to Here" isn't so much about the impossibility of time travel as it is about that bigger mystery of entropy. Why does the arrow of time fly in just one direction, and where did that arrow come from, anyway? Does it make sense to talk about what happened before the arrow flew?
Some physicists would say such questions can't be discussed in scientific terms. But Carroll isn't one of those physicists. After explaining in detail what we know about entropy and its relation to the arrow of time, he moves on to the more speculative side of the issue.

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Royal Institution of Christmas Lectures
Arrows of Time
Lecturer: Dr Neil Johnson
Year: 1999

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Crystallizing Block Universe
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Title: Time and Spacetime: The Crystallizing Block Universe
Authors: George F. R. Ellis, Tony Rothman

The nature of the future is completely different from the nature of the past. When quantum effects are significant, the future shows all the signs of quantum weirdness, including duality, uncertainty, and entanglement. With the passage of time, after the time-irreversible process of state-vector reduction has taken place, the past emerges, with the previous quantum uncertainty replaced by the classical certainty of definite particle identities and states. The present time is where this transition largely takes place, but the process does not take place uniformly: Evidence from delayed choice and related experiments shows that isolated patches of quantum indeterminacy remain, and that their transition from probability to certainty only takes place later. Thus, when quantum effects are significant, the picture of a classical Evolving Block Universe ('EBU') cedes place to one of a Crystallizing Block Universe ('CBU'), which reflects this quantum transition from indeterminacy to certainty, while nevertheless resembling the EBU on large enough scales.

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"The Arrow of Time
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"The Arrow of Time", Professor Sean Carroll

Date/Time: Monday, 23 November 2009, 6:00 pm to 8:00 pm
Location: Union Hall, North Terrace Campus
Cost: FREE

Professor Sean Carroll, Senior Research Associate - Physics
California Institute of Technology (Caltech)

Unlike distance, time has a direction, pointing from past to future. Sean Carroll will examine this arrow of time, which is deeply engraved in the universe around us.
Why do we remember the past, but not the future? Why don't we meet people who grow younger as they age? Why do things, left by themselves, tend to become messier and more chaotic? What would Maxwell's Demon say to a Boltzmann Brain? The answers can be traced to the moment of the Big Bang -- or possibly before.
Time pervades our lives -- we keep track of it, lament its loss, put it to good use. The rhythms of our clocks and our bodies let us measure the passage of time, as a ruler lets us measure the distance between two objects. But unlike distances, time has a direction, pointing from past to future. From Eternity to Here examines this arrow of time, which is deeply ingrained in the universe around us. The early universe -- the hot, dense, Big Bang -- was very different from the late universe -- cool, empty, expanding space -- and that difference is felt in all the workings of Nature, from the melting of ice cubes to the evolution of species.
The arrow of time is easy to perceive, much harder to understand. Physicists appeal to the idea of entropy, the disorderliness of a system, which tends to increase according to the celebrated Second Law of Thermodynamics.
But why was entropy ever small in the first place?
That's a question that has been tackled by thinkers such as Ludwig Boltzmann, Stephen Hawking, Richard Feynman, Roger Penrose, and Alan Guth, all the way back to Lucretius in ancient Rome. But the answer remains elusive.
The only way to understand the origin of entropy is to understand the origin of the universe -- by asking what happened at the Big Bang, and even before.

Source University of Adelaide

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Ed ~ Quantum smearing may have affected the origin of time.
Quantum fuzziness affects Space and time 'units', (10^-33cm of space & 10^-43 seconds of time). Time may have started as (or still is) a space dimension. It may even revert back to a spatial dimension in the distant future...
Another question that arises is why do particles move 'through' time?
If we go back to understanding why particles move through normal space then we can perhaps shed some light on 'time-travel'. Newtonian physics dictate that particles only move in a straight line when they are/have been given an external force. Hum, so particles not acted upon will stay put. And if we remember that particles are really only potentials existing in a gauge field; then we can see that perhaps time maybe related to a physical movement through a spatial dimension. The big-bang gave the universe 'energy' to expand, ( space is really expanding), Perhaps the big-bang gave the matter in the universe the energy to travel through a spatial dimension (that became the time-dimension)? This 'Time-energy' could be independent to the spatial expansion. Time could perhaps 'slow down' (or reverse) as perhaps an expanding universe eventually could; We know that gravity affects Time.

How does this new theory fit general relativity?
We know that there is no 'universal' time; Every particle and every observer has his or her own relative time. A large length of string viewed 'end-on' seems to have zero length...
When we view time from a spatial perspective then it is easy to understand why time can a vary.
If time were related to the expansion rate of the universe we would see a linear graph of stellar distances/time (using the Hubble constant). But other cosmic forces (not related to the initial big-bang) such as dark matter or dark-energy may distort the graph.

When we describe space, we tend to describe a coordinate system in three dimensions. However, the universe probably consists of at least 10 dimensions , with an extra dimension that has been isolated as a 'temporal' dimension. It could be argued that ultimately all the dimensions are fundamentally the same. And that a spatial dimension cannot be divided indefinitely small, the limiting factor would be the quantum nature of space (10^-42cm). This Planck length translates directly with the Planck-time quantum unit.

A lot of people associate time with the flow of entropy; this is only a real- world product of the interaction of Feynman-Wheeler advancing and retarding waves.

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Mysteries of time, and the multiverse

Caltech physicist Sean M. Carroll has been wrestling with the mystery of time. Most physical laws work equally well going backward or forward, yet time flows only in one direction. Writing in this month's Scientific American, Carroll suggests that entropy, the tendency of physical systems to become more disordered over time, plays a crucial role. Carroll sat down recently at Caltech to explain his theory.

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Ed ~ The Feynman-Wheeler theory of time describes how every particle emits two opposite carrier waves; a 'retarded' wave and an 'advanced' wave. The waves travel `through` time; one forward and one backwards. It is the interaction (or absorbsion) with other temporal waves that give the particles a sense of `movement` through time. When a particle absorbs a wave it also emits a retarded and advanced wave. In the original theory the density of the universe plays a critical part; in that, the retarded wave have to be (mostly) all absorbed by matter or else the interference amount drops.
It has to be said that experiments to find advanced waves have found none.
But perhaps the direction/absorbsion is decided by the boundary conditions of the universe; at one end there is the Big-bang (this reflects the wave) and the other end (future) is open (the wave cannot be reflected), and full of virtual particles.
Are these waves present in our normal 3 spatial dimensions?
They don't appear to be.

Maxwell's equations can be used to show that the electric and magnetic fields obey wave equations.

The speed c of an electromagnetic wave is determined by the constants of electricity and magnetism :
c = 1/(e_0m_0)^ = 2.998 X 10^8m/s.

Light is an electromagnetic wave: this was discovered around 1864, as soon as the equation c = 1/(e_0m_0)^ = 2.998 X 10^8m/s was discovered, since the speed of light had been accurately measured by then, and its agreement with c was not likely to be a coincidence.
Maxwell's electromagnetic wave equation permits forward and backward-in-time waves.

We could assume that they cancel each other out in our 'normal' space. But is it possible that these waves are actually travelling through compactified spatial dimension?
These compactified dimensions could be like tiny 'wormholes' that could connect to the future or past...This would allow a particle using its' retarded/advanced waves to propagate and interact/interfere with itself...
Does that imply that the Time-dimension is only an illusion?
So perhaps time does not flow; because there is nothing too flow ; Time maybe only an illusion caused by the interaction/interference of opposite waves, travelling through compactified spatial dimensions.
So what does that imply for the interaction of the 5 dimensional membranes that created the big-bang?
Time could not exist in the same sense that we would recognise; in fact we could go as far to say that 'time' did not exist 'before' the big-bang.
Time, and the arrow of time, was created at the big-bang event.

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