Tag Archives: Stephen Hawking

The Quantum Universe and the Uncertainty Principle

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Guest post by Frikkie de Bruyn

SUPPOSE you want to order breakfast in a restaurant and the waiter gives you a menu of thousands of different choices. Some of the choices may be closer to what you want to order but every choice is subject to a probability that you may or may not get it. One choice may offer you bacon prepared in thousands of different ways, another an egg prepared in thousands of different ways. Every probability is subject to a chance that you may or may not get it.

You wonder if you’re still on Earth and leave the restaurant in disgust. What’s going on? This is an example of quantum logic and uncertainty.

Heisenberg Uncertainty Principle (Image: www.chmcs.tumblr.com)In the quantum world, this logic reigns supreme. At the quantum level, the principle of uncertainty manifests itself in the form of quantum fluctuations. These may be seen as fluctuations in the energy levels and the formation of virtual particles and anti-particles annihilating within the limits set by the uncertainty principle. The greater the energy fluctuations, the greater the energy borrowed by the virtual particles. This means that the times for the energy to be repaid by the particles are getting shorter and shorter.

However, generally provided that these exchanges take place in times between the Compton time (10-23 s) and the Planck time (10-43 s) all is well. This is important for the very early Universe as we shall see below. We are not aware of this apparently chaotic scene because of what some scientists calls decoherence.

Traveling in an aircraft high above the ocean you are oblivious to the high waves on the ocean far below because your eyes cannot see the waves at that altitude. The same happens to uncertainties at the quantum level. You may not be aware of the quantum fluctuations and uncertainties, but it is very real indeed. All computers use the tunneling effect at the quantum level; without it there will be no computers. But what has this to do with the Universe?

If we follow Einstein’s equations to the end, the Universe started out from a point of infinite density, gravity and temperature. This is the conclusion Prof. Stephen Hawking and Dr. Roger Penrose reached and for which Hawking received his Doctorate. They also concluded that the size of the Universe in the beginning must have been smaller than the nucleus of an atom, in other words, a quantum object.

In quantum mechanics there are, however, no infinities! Hawking further reached the conclusion that the principles and laws of general relativity break down at the Big Bang. He realized why these apparent discrepancies between general relativity and quantum mechanics occurred and he subsequently conceded that it was wrong to apply general relativity to a quantum object, since Einstein’s equations cannot handle the incredible densities, gravity and temperature at the quantum level.

We must replace the word ‘infinities’ with ‘incredible’ and we have to conclude that the Universe started out as a quantum object subject to all the uncertainties, laws and principles of quantum mechanics.

The quantum object from which the Universe originated can be described as a primordial quantum vacuum. A chance quantum fluctuation, also described as false vacuum energy, released an incredible amount of energy causing the Universe to expand exponentially. Hawking described the origin of the energy as the quantum vacuum having borrowed the energy from gravity, meaning that there is no need for the energy to be repaid in the present epoch of the Universe. Was there a minimum size of the Universe at the Big Bang? Quantum mechanics tells us that there probably was; the Planck length of 10-33 cm. But we have to be careful.

How can we know?

We cannot determine experimentally if that size even exists and what the energy levels will be. Even if it does exist then the energy levels were probably so high that any chance fluctuation could have pushed it over the limit to form a black hole. Current theoretical research seems to point more and more to the probability that the very early Universe had a minimum size. But it must be emphasized that temperature, gravity and densities were so enormously high that it cannot be recreated in even the most advanced particle accelerators on Earth.

The very early Universe can therefore only be theoretically studied. Any conclusions that the very early Universe may or may not have had a minimum size are always subject to the uncertainties of quantum mechanics. It will nevertheless be of considerable significance if the conclusions turn out to be correct.

Continue Reading …

Frikkie de Bruyn is the Director of the Cosmology
Section of the Astronomical Society of Southern Africa

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Perceptions of Time – Frikkie de Bruyn

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TIME: It’s not as simple as it seems

IF you were abducted by aliens and asked to describe Earth’s air in a language you understood, how would you describe it? It would be equally difficult to describe left and right without any points of reference. The same hypothetical can be applied to time — that dimension we all thought we knew until we were asked to describe it.

It’s natural to think of time as a linear progression. Experience will tell us that we live and we die; that the season’s come and go; that the sun rises and it sets. All these have a beginning and an end. Astronomical ClockQuantum physicists will argue differently — that time is far more precarious than we are conditioned to believe. When asked the question “what happened before the Big Bang?” physicists will most likely scoff at the notion and argue that space and time itself did not exist before the Big Bang. Without time, the notion of “before” becomes meaningless. It would be like asking “what’s south of the South Pole” if the Earth was the only object we knew existed.

But there’s no escaping our notion of time. Everything we do or experience takes place at a specific time and point in space. We all “experience” time, but can we ever be sure that it exists, out there, independent of our experience? Cosmologist, Frikkie de Bruyn, offers some insight into the precarious nature of time to help us better understand its nature.

“Time is experienced in two fundamental ways, explains de Bruyn. It seems to flow like a river, the seconds, days and years passing relentlessly. Our perception of time is also characterised by a succession of moments with a clear distinction between past, present and future.”

We can all confidently say that we have knowledge about out past experiences, but not of the future. However, at any given point in time, our past and future are connected to what we describe as the “now”. Some go as far as to argue that all that exists is the “now”.

Time as Linear or Cyclic
These perceptions of time are closely related to the idea of time being either linear or cyclic. It’s natural to assume that time is linear, with clearly defined beginnings and ends to most human experiences and unique events. “It is like a giant ruler, stretching back into the past marked in scale of years, decades and centuries and it stretches away into the future,” explains de Bruyn. The Big Bang theory also uses this “progressive” perception of time.

Day BreakHowever, cosmologists like de Bruyn will argue that most of the time, time appears to be cyclical and not necessarily progressive. Cycles occurring in nature, such as the days, seasons and years can be used to support this perception. Time therefore becomes “the element in which natural events occur,” says de Bruyn.

We have always been limited by our language when it comes to describing something like perception of time, yet it nonetheless remains central to our modern lives. GPS devices would not exist without pinpoint accuracy in timing, computers and networks wouldn’t work and we couldn’t have landed a man safely on the moon.

Changes in perception of time
The invention of the clock and subsequently the watch brought about a new awareness of time. “Our minds process information from clocks and ‘interpret’ that information as ‘being time’”, explains de Bruyn. Another greatly significant revolution in our perception of time was Einstein’s theory of relativity.

“The Newtonian perception of time as separate and independent, ticking away irrespective of human activities, was replaced by the ‘personalised’ relative interpretation of time. Every person had his own time”, says de Bruyn.

At a more cosmological level, we now also know that time slows down as we approach velocities close to the speed of light. Stephen Hawking even described time as coming to a complete end within a black hole.

Einstein’s relativity theory also allowed us to think of time as a measure of the separation of events in space — clearly connected to change. However, time does not exist in the sense of objects and changes. “It is a human invention that provides a mental tool to measure change, and change means events separated in space”, explains de Bruyn.

It should be difficult for anyone to consider time as a human invention; that our concept of time is so closely related to space — the spatial separation of objects and change. It’s even more difficult to comprehend, that outside of this context, time simply has no existence.

It makes one wonder: if we discovered the secret to timeless longevity, where death was not feared as the end, would we still be so obsessed with time?

Source: Frikkie de Bruyn, Director of the Cosmology Section of the Astronomical Society of Southern Africa.