Tag Archives: quantum fluctuation

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Virtual Particles – Spontaneous Particle Creation

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This article is from chapter 1 of my book, Unraveling the Universe’s Mysteries. Enjoy!

Spontaneous particle creation is the phenomenon of particles appearing from apparently nothing (i.e., a vacuum), hence their name “virtual particles.” However, they appear real, and cause real changes to their environment. What is a virtual particle? It is a particle that only exists for a limited time. The virtual particle obeys some of the laws of real particles, but it violates other laws. What laws do virtual particles obey? They obey two of the most critical laws of physics, the Heisenberg uncertainty principle (it is not possible to know both the position and velocity of a particle simultaneously), and the conservation energy (energy cannot be created or destroyed). What laws do they violate? Their kinetic energy, which is the energy related to their motion, may be negative. A real particle’s kinetic energy is always positive. Do virtual particles come from nothing? Apparently, but to a physicist, empty space is not nothing. Said more positively, physicists consider empty space something.

Before we proceed, it is essential to understand a little more about the physical laws mentioned in the above paragraph.

First, we will discuss the Heisenberg uncertainty principle. Most physics professors teach it in the context of attempting to simultaneously measure a particle’s velocity and position. It goes something like this:

  • When we attempt to measure a particle’s velocity, the measurement interferes with the particle’s position.
  • If we attempt to measure the particle’s position, the measurement interferes with the particles velocity.
  • Thus, we can be certain of either the particle’s velocity or the particle’s position, but not both simultaneously.

This makes sense to most people. However, it is an over simplification. The Heisenberg uncertainty principle has greater implications. It embodies the statistical nature of quantum mechanics. Quantum mechanics is a set of laws and principles that describes the behavior and energy of atoms and subatomic particles. This is often termed the “micro level” or “quantum level.” Therefore, you can conclude that the Heisenberg uncertainty principle embodies the statistical behavior of matter and energy at the quantum level. In our everyday world, which science terms the macro level, it is possible to know both the velocity and position of larger objects. We generally do not talk in terms of probabilities. For example, we can predict the exact location and orbital velocity of a planet. Unfortunately, we are not able to make similar predictions about an electron as it obits the nucleus of an atom. We can only talk in probabilities regarding the electron’s position and energy. Thus, most scientists will say that macro-level phenomena are deterministic, which means that a unique solution describes their state of being, including position, velocity, size, and other physical attributes. On the other hand, most physics will argue that micro level (quantum level) phenomena are probabilistic, which means that their state of being is described via probabilities, and we cannot simultaneously determine, for example, the position and velocity of a subatomic particle.

The second fundamental law to understand is the conservation of energy law that states we cannot create or destroy energy. However, we can transform energy. For example, when we light a match, the mass and chemicals in the match transform into heat. The total energy of the match still exists, but it now exists as heat.

Lastly, the kinetic energy of an object is a measure of its energy due to its motion. For example, when a baseball traveling at high velocity hits a thin glass window, it is likely to break the glass. This is due to the kinetic energy of the baseball. When the window starts to absorb the ball’s kinetic energy, the glass breaks. Obviously, the thin glass is unable to absorb all of the ball’s kinetic energy, and the ball continues its flight after breaking the glass. However, the ball will be going slower, since it has used some of its kinetic energy to break the glass.

With the above understandings, we can again address the question: where do these virtual particles come from? The answer we discussed above makes no sense. It is counter intuitive. However, to the best of science’s knowledge, virtual particles come from empty space. How can this be true?

According to Paul Dirac, a British physicist and Nobel Prize Laureate, who first postulated virtual particles, empty space (a vacuum) consists of a sea of virtual electron-positron pairs, known as the Dirac sea. This is not a historical footnote. Modern-day physicists, familiar with the Dirac-sea theory of virtual particles, claim there is no such thing as empty space. They argue it contains virtual particles.

This raises yet another question. What is a positron? A positron is the mirror image of an electron. It has the same mass as an electron, but the opposite charge. The electron is negatively charged, and the positron is positively charged. If we consider the electron matter, the positron is antimatter. For his theoretical work in this area, science recognizes Paul Dirac for discovering the “antiparticle.” Positrons and antiparticles are all considered antimatter.

Virtual particle-antiparticle pairs pop into existence in empty space for brief periods, in agreement with the Heisenberg uncertainty principle, which gives rise to quantum fluctuations. This may appear highly confusing. A few paragraphs back we said that the Heisenberg uncertainty principle embodies the statistical nature of energy at the quantum level, which implies that energy at the quantum level can vary. Another way to say this is to state the Heisenberg uncertainty principle gives rise to quantum fluctuations.

What is a quantum fluctuation? It is a theory in quantum mechanics that argues there are certain conditions where a point in space can experience a temporary change in energy. Again, this is in accordance with the statistical nature of energy implied by the Heisenberg uncertainty principle. This temporary change in energy gives rise to virtual particles. This may appear to violate the conservation of energy law, arguably the most revered law in physics. It appears that we are getting something from nothing. However, if the virtual particles appear as a matter-antimatter pair, the system remains energy neutral. Therefore, the net increase in the energy of the system is zero, which would argue that the conservation of energy law remains in force.

No consensus exists that virtual particles always appear as a matter-antimatter pair. However, this view is commonly held in quantum mechanics, and this creation state of virtual particles maintains the conservation of energy. Therefore, it is consistent with Occam’s razor, which states that the simplest explanation is the most plausible one, until new data to the contrary becomes available. The lack of consensus about the exact nature of virtual particles arises because we cannot measure them directly. We detect their effects, and infer their existence. For example, they produce the Lamb shift, which is a small difference in energy between two energy levels of the hydrogen atom in a vacuum. They produce the Casimir-Polder force, which is an attraction between a pair of electrically neutral metal plates in a vacuum. These are two well-known effects caused by virtual particles. A laundry list of effects demonstrates that virtual particles are real.

Close-up view of translucent blue spherical cells or microscopic organisms against a dark background.

Virtual Particles – Something from Nothing – Part 2/3

Categories, Universe Mysteries, , , , ,

This three part post is the first chapter of my book, Unraveling the Universe’s Mysteries. Here is part 2. Enjoy!

According to Paul Dirac, a British physicist and Nobel Prize Laureate, who first postulated virtual particles, empty space (a vacuum) consists of a sea of virtual electron-positron pairs, known as the Dirac sea. This is not a historical footnote. Modern-day physicists, familiar with the Dirac-sea theory of virtual particles, claim there is no such thing as empty space. They argue it contains virtual particles.

This raises yet another question. What is a positron? A positron is the mirror image of an electron. It has the same mass as an electron, but the opposite charge. The electron is negatively charged, and the positron is positively charged. If we consider the electron matter, the positron is antimatter. For his theoretical work in this area, science recognizes Paul Dirac for discovering the “antiparticle.” Positrons and antiparticles are all considered antimatter.

Virtual particle-antiparticle pairs pop into existence in empty space for brief periods, in agreement with the Heisenberg uncertainty principle, which gives rise to quantum fluctuations. This may appear highly confusing. A few paragraphs back we said that the Heisenberg uncertainty principle embodies the statistical nature of energy at the quantum level, which implies that energy at the quantum level can vary. Another way to say this is to state the Heisenberg uncertainty principle gives rise to quantum fluctuations.

What is a quantum fluctuation? It is a theory in quantum mechanics that argues there are certain conditions where a point in space can experience a temporary change in energy. Again, this is in accordance with the statistical nature of energy implied by the Heisenberg uncertainty principle. This temporary change in energy gives rise to virtual particles. This may appear to violate the conservation of energy law, arguably the most revered law in physics. It appears that we are getting something from nothing. However, if the virtual particles appear as a matter-antimatter pair, the system remains energy neutral. Therefore, the net increase in the energy of the system is zero, which would argue that the conservation of energy law remains in force.

No consensus exists that virtual particles always appear as a matter-antimatter pair. However, this view is commonly held in quantum mechanics, and this creation state of virtual particles maintains the conservation of energy. Therefore, it is consistent with Occam’s razor, which states that the simplest explanation is the most plausible one, until new data to the contrary becomes available. The lack of consensus about the exact nature of virtual particles arises because we cannot measure them directly. We detect their effects, and infer their existence. For example, they produce the Lamb shift, which is a small difference in energy between two energy levels of the hydrogen atom in a vacuum. They produce the Casimir-Polder force, which is an attraction between a pair of electrically neutral metal plates in a vacuum. These are two well-known effects caused by virtual particles. A laundry list of effects demonstrates that virtual particles are real.

The above discussions distill to three key points. First, in accordance with the Heisenberg uncertainty principle, virtual particles pop in and out of existence in a vacuum. Second, we cannot measure virtual particles directly. Third, modern science believes virtual particles are real because they cause measurable changes to their environment.

This creation of virtual particles is sometimes termed spontaneous particle creation. Spontaneous particle creation raises an intriguing question. Are there hidden dimensions? Assume the Dirac sea model is correct, and that empty space (a vacuum) consists of a sea of virtual electron-positron pairs. If you are willing to accept this assumption, where are they located? It is a reasonable question. We are dealing with a vacuum, and at the same time asserting it contains electron-positron pairs. Where are they located? A possible explanation is they are in another dimension. As mind bending as this sounds, a formidable scientific theory known as M-theory asserts reality consists of eleven dimensions, not simply the four (three spatial, one temporal) we typically encounter. M-theory is “string” theory on steroids. At this point, I suspect you may be ready to blow a time-out whistle. This theory explains one puzzle using another puzzle. Therefore, in the interest of clarity, we will take it one step at a time, and start by explaining more about M-theory. This will be a conceptual modeling of the theory.

In a sense, science has been working its way to M-theory since the discovery of atoms and subatomic particles, culminating in the discovery of the quarks (circa 1970s) as the fundamental building blocks for protons and neutrons. (Protons, neutrons, and electrons are the fundamental building blocks of atoms. Quarks are the fundamental building blocks of protons and neutrons.) In the 1980s, scientists claimed that these fundamental building blocks could be further reduced to infinitely small building blocks of vibrating energy, having only the dimension of length, termed “stings.”

Conceptually, the “strings” vibrate in multiple dimensions. The vibration of the string determines whether it appears as matter or energy. According to string theory, every form of matter or energy is the result of the string’s vibration.

By the 1990s, science recognized five different string theories, each with their own set of equations. The five string theories appeared valid, but scientists became uneasy. Surely, they could not all be right. In 1994, string theorist Edward Witten (Institute for Advanced Study), and other researchers, proposed a unifying theory called “M-theory.” The “M” stands for “membrane.” M-theory asserted that strings are one-dimensional slices of a two-dimensional membrane vibrating in eleven-dimensional space.

I understand it is hard, if not impossible, to picture an eleven-dimensional space because we live in a four-dimensional world. My picture goes something like this. The membrane (referred to as a “brane”) is like a shadow of a million spread-out toothpicks. A shadow has two dimensions, and is the brane in this analogy. Each toothpick represents a string, having only the dimension of length. In this example, we are considering the toothpicks to have no width. Next, I think about this shadow being able to float off the surface and move around the room in three-dimensional space. It continually changes position in time. That is to say at time t1, it is in one place, and at another time t2, it is in another place. In this mind-bending analogy, we have accounted for seven dimensions. A two-dimensional shadow made from one-dimensional toothpicks accounts for three dimensions. The shadow floating in three-dimensional space accounts for three additional dimensions. Now, picture the shadow floating to a specific place at a specific time. When it moves to another place, time will have passed. The shadow, changing positions in time, accounts for one additional dimension (a temporal coordinate). How do I picture the other four? I think of there being small, invisible holes in space. The shadow can slip into, move around in, and disappear from view in these holes. The holes would represent a hidden three-dimensional space accounting for another three dimensions. The shadow moving in the holes would again represent another temporal coordinate. This analogy, which may be difficult to understand, is how I picture eleven-dimensional space. We live in a four-dimensional world. It is difficult to imagine seven other hidden dimensions.

Scientists, too, have a problem with the eleven-dimensional model of reality that M-theory provides. The mathematics of M-theory is elegant, but correlating the mathematics to reality has frustrated numerous scientists. However, M-theory did accomplish one main goal. It unified the previous five spring theories into one. It demonstrated that each of the five was a specific case of M-theory. Well-known scientists, like Michio Kaku, Stephen Hawking, and Leonard Mlodinow, became proponents of M-theory, applauding its mathematical elegance, and suggesting it may be a candidate for The Theory of Everything. (The Theory of Everything would be a comprehensive scientific theory that explains the physical behavior of all matter and energy.) The one thing missing to make this picture perfect is experimental evidence. To date, we have no experimental evidence for M-theory. This does not mean M-theory is wrong or should be dismissed. Scientists continue to work on it, and experimental proof may eventually emerge.

“Fascinating,” as Mr. Spock would say on Star Trek, but where does that leave us? Why am I bringing up M-theory and hidden dimensions? The answer is that spontaneous particle creation may have a connection to the hidden dimensions of M-theory. The entire Dirac sea (a vacuum filled with particle-antiparticle pairs) may exist in the hidden dimensions predicted by M-theory. Of course, it is easy for me, a theoretical physicist, to make this assertion since we have no proof of M-theory. However, we do have experimental evidence that enables us to infer that virtual particles exist. If they do exist, where are they located? Even if they exist as pure packets of energy (quanta), where are they located? One suggestion is to look into the hidden dimensions predicted by M-theory.

Stay tuned for part 3 (conclusion)