Choices and the Uncertainty Principle cont.

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Read part 1 of Choices and the Uncertainty Principle here

THE reason that the laws of general relativity break down at the Big Bang is that it does not incorporate the most basic tenet of quantum theory – the uncertainty principle – the element that Einstein could never accept.

Quantum theory tells us that the very early Universe must have had a multitude of choices. It could have formed a black hole, there could have been no expansion of the Universe, the strength of gravity could have been stronger or weaker and there could have been no matter in the Universe, only radiation. All of these choices would have resulted in a still-born Universe.

The multitude of choices and resulting uncertainties form the basis of quantum theory. But the Universe, as big as it is today, is still subject to the uncertainties. It is like a gambler throwing the dice – there are a large number of possible rolls of the dice. It is interesting to note that in a large object such as the Universe, the multitude of choices average out to something we can predict. That is why we can apply Einstein’s theory so successfully to the Universe as a whole.

Scientists also refer to the multitude of choices as multiple histories. The well-known American theoretical physicist, Richard Feynman, has developed a mathematical framework to calculate the most probable outcome of multiple histories. The same formulae can be applied to determine the most likely position of an electron. Again, the closer we determine an electron’s position, the larger its velocity will be.

The uncertainties of the quantum world are not imaginary; they are real. Feynman’s multiple histories idea of the Universe is now incorporated into general relativity to form a unified theory which could be used to calculate how the Universe will develop if we know how the histories started.

Perceptions of time

What does quantum theory tell us about time in the Universe? Time does not exist in quantum theory! At least it does not exist in the sense that most of us think about it. There is no clock out there ticking no matter what happens in the Universe. Time in quantum theory is simply the measurement of a process, like the decay of radioactive matter.

Clocks developed to measure such processes cannot measure any duration of time smaller than a billionth-billionth of a second. This is more or less the size of an atom or, more precisely, the time it will take a photon to cross the size of an atom. This interpretation of time is in line with Einstein’s general relativity. Measurement of the duration of processes at the quantum level is subject to the uncertainties and fuzziness typical of quantum theory.

We cannot measure the duration of time it takes a particle to acquire a certain amount of energy. The more accurately we measure the energy, the less accurate can we measure the time it took the particle to gain the energy. This is why the formation of particles (matter) in the early Universe is subject to the uncertainty principle of quantum mechanics.

Feeling uncertain?

People do not like uncertainties and therefore most do not like quantum mechanics. As a scientist put it: “I do not like quantum mechanics, but I use it because it works”. The velocity of particles in the early Universe must have been incredibly high due to the high energy levels. If you use such a particle to determine time, you would find that a particle traveling at the speed of light gives you the age of the Universe as NIL.

All particles must have been traveling at very close to the speed of light. It becomes clear that every particle had its own time. Whose time is correct? All readings of time are correct depending on your velocity and the gravitational pull. Einstein said: “every observer’s time is correct”. There is no intrinsic unchanging time.

What is reality?

I want to end with a few thoughts about our relationship at the macroscopic level with the microscopic world. In everyday life you never see a single photon and the microscopic world seems so remote and unreal. If you think further, you realize that almost everything in our everyday world is the way it is because of the quantum world. Matter has bulk because atoms have size. The colours, textures, hardness and the transparency of materials all depend on the exclusion principle regulating the behaviour of electrons in atoms. The list could go on, but ultimately the macroscopic world is what it is because of the microscopic world.

The quantum world is not something remote. It forms part of all matter. Take this page; look at it at ever smaller distances and time scales and the apparent mad world I have described above will unfold before your eyes. The problem is, currently we can only access the quantum world theoretically because technology has not developed so far that we can access it in any other way.

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

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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.

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. Quantum 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.

However, 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.

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The evolution of stars in the universe

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THE lunar eclipse the other night got me in awe of space again. It’s amazing to think that without stars there would be no planets, no galaxies, no light and no life. Our exploding balls of gas in the sky can be thought of as giant factories or furnaces that manufacture the elements and scatter them across the universe. All the base elements that together make up planet Earth are thanks to the stars. Even the heavier elements, such as iron, have been cooked within stars and rained down on Earth. All inhabitants, including you are me, are made up of these elements. So essentially, we are all stardust. Here’s how it all began.

In the beginning…

About 380 000 years after the Big Bang, the universe consisted of gas — mainly hydrogen and helium. The universe at that time was like a giant star- forming area, where the process of fragmentation and star-forming was clearly visible. The types of stars that formed then were very different from the stars today. This was because the contents of the early universe still lacked carbon, oxygen, iron or any of the other elements that we are familiar with today.

The first generation of stars were massive — hundreds of times the mass of the sun. However, they were too hot to manufacture any metals and needed to cool in order to do so.

According to Frikkie de Bruyn, the director of the Cosmology Section of the Astronomical Society of Southern Africa­, “There is a theoretical limit to how big a star can be because of the balancing act of light, pressure and gravitational collapse. Once a star gets too big it generates so much light, heat and pressure at the core of the star that it starts blowing off the outer layers of its atmosphere faster than in falling gas due to gravitational collapse.”

The gas blowing off in the surrounding space has the affect of forming more stars. De Bruyn explains that “until that time the whole universe was opaque to light, like a very thick fog. When the first stars formed they created light, ionized the gas and made it transparent. It was almost as if a giant switch was flipped and for the first time the universe was lit up”.

These first generation stars emitted strong ultraviolet radiation and very powerful stellar winds that blasted enormous cavities in the surrounding gas. Unfortunately, we are unable to observe these first generation stars, but De Bruyn says that astronomers have been able to detect a faint, infrared glow attributed to these early stars in the universe.

The second generation stars

The super massive first generation stars were only around for a few million years, which is a relatively short life span in cosmological terms. Like the stars we stare at today, they fused together heavier elements and eventually went supernova. They did not create much carbon or oxygen at this point, but did leave behind lots of iron, explains De Bruyn.

The second generation stars, also known as population II stars, formed before the first generation stars died — formed from the gas clouds left behind when the first generation stars exploded. These population II stars were also extremely low in metals, but the overlap between their formation and the death of their ancestors, resulted in an interesting mixture of first and second generation stars.

Population II stars were smaller but slightly hotter than the stars we know today. Their metal contents gradually started to increase. However, there is a mystery, explains de Bruyn. “As far as can be established only two second generation stars were found. Astronomers refer to this as the missing G-dwarf star. Spectroscopic analysis reveal that these stars are metal poor. They are mainly to be found in globular clusters, in the halo of the Milky Way.”

Population I stars

In the disc of the Milky Way galaxy, we find metal-rich Population I stars. These beauties contain carbon, hydrogen and iron, and are capable of forming planets. This occurs when all the atoms heavier than helium start clumping together.

So we find ourselves in a metal-rich part of the galaxy. The metal contents of the earliest stars were between 200 000 and 300 000 times less than our metal-rich sun. As these stars developed and reproduced, we now have stars that are three and a half times more metal-rich than the sun. De Bruyn­ says that a very interesting area of current research in cosmology is to determine the possibility of stars having planets according to their richness in metals.

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

“You are a child of the universe no less than the trees and the stars; you have a right to be here. And whether or not it is clear to you, no doubt the universe is unfolding as it should” – Max Ehrmann, Desiderata

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