Category Archives: Physics

A black and white image of a clock face with a spiral effect distorting the numbers and hands.

Reverse Causality – The Future Can Change the Past

Categories, Physics, Time Travel, Universe Mysteries, , , , , ,

Most people find reverse causality intriguing, but impossible. Yet, it has a strong basis in science. In my book, How to Time Travel, I discuss a number of reverse causality examples. Here are some from the book.

Twisting the Arrow of Time

The flow of time, sometimes referred to as the “arrow of time,” is a source of debate, especially among physicists. Most physicists argue that time can only move in one direction based on “causality” (i.e., the relationship between cause and effect). The causality argument goes something like this: every event in the future is the result of some cause, another event, in the past. This appears to make perfect sense, and it squares with our everyday experience. However, experiments within the last several years appear to argue reverse causality is possible. Reverse causality means the future can and does influence the past. For example, in reverse causality, the outcome of an experiment is determined by something that occurs after the experiment is done. The future is somehow able to reach into the past and affect it. Are you skeptical? Skepticism is healthy, especially in science. Let us discuss this reverse causality experiment.

In 2009, physicist John Howell of the University of Rochester and his colleagues devised an experiment that involved passing a laser beam through a prism. The experiment also involved a mirror that moved in extremely small increments via its attachment to a motor. When the laser beam was turned on, part of the beam passed through the prism, and part of the beam bounced off the mirror. After the beam was reflected by the mirror, the Howell team used “weak measurements” (i.e., measurement where the measured system is weakly affected by the measurement device) to measure the angle of deflection. With these measurements, the team was able to determine how much the mirror had moved. This part of the experiment is normal, and in no way suggests reverse causality. However, the Howell team took it to the next level, and this changed history, literally. Here is what they did. They set up two gates to make the reflected mirror measurements. After passing the beam through the first gate, the experimenters always made a measurement. After passing it through the second gate, the experimenters measured the beam only a portion of the time. If they chose not to make the measurement at the second gate, the amplitude of the deflected angle initially measured at the first gate was extremely small. If they chose to make the measurement at the second gate, the deflected angle initially measured at the first gate was amplified by a factor of 100. Somehow, the future measurement influenced the amplitude of the initial measurement. Your first instinct may be to consider this an experimental fluke, but it is not. Physicists Onur Hosten and Paul Kwiat, University of Illinois at Urbana-Champaign, using a beam of polarized light, repeated the experiment. Their results indicated an even larger amplification factor, in the order of 10,000.

The Double-Slit Experiment

There are numerous versions of the double-slit experiment. In its classic version, a coherent light source, for example a laser, illuminates a thin plate containing two open parallel slits. The light passing through the slits causes a series of light and dark bands on a screen behind the thin plate. The brightest bands are at the center, and the bands become dimmer the farther they are from the center.

The series of light and dark bands on the screen would not occur if light were only a particle. If light consisted of only particles, we would expect to see only two slits of light on the screen, and the two slits of light would replicate the slits in the thin plate. Instead, we see a series of light and dark patterns, with the brightest band of light in the center, and tapering to the dimmest bands of light at either side of the center. This is an interference pattern and suggests that light exhibits the properties of a wave, which is well accepted in the scientific community. This is termed the dual nature of light. This portion of the double-slit experiment simply exhibits the wave nature of light.

The above double-slit experiment demonstrates only one element of the paradoxical nature of light, the wave properties. The next part of the double-slit experiment continues to puzzle scientists. There are five aspects to the next part.

1. Both individual photons of light and individual atoms have been projected at the slits one at a time. This means that one photon or one atom is projected, like a bullet from a gun, toward the slits. Surely, our judgment would suggest that we would only get two slits of light or atoms at the screen behind the slits. However, we still get an interference pattern, a series of light and dark lines, similar to the interference pattern described above. Two inferences are possible:

a. The individual photon light acted as a wave and went through both slits, interfering with itself to cause an interference pattern.
b. Atoms also exhibit a wave-particle duality, similar to light, and act similarly to the behavior of an individual photon light described (in part a) above.

2. Scientists have placed detectors in close proximity to the screen to observe what is happening, and they find something even stranger occurs. The interference pattern disappears, and only two slits of light or atoms appear on the screen. What causes this? Quantum physicists argue that as soon as we attempt to observe the wavefunction of the photon or atom, it collapses. Please note, in quantum mechanics, the wavefunction describes the propagation of the wave associated with any particle or group of particles. When the wavefunction collapses, the photon acts only as a particle.

3. If the detector (in number 2 immediately above) stays in place but is turned off (i.e., no observation or recording of data occurs), the interference pattern returns and is observed on the screen. We have no way of explaining how the photons or atoms know the detector is off, but somehow they know. This is part of the puzzling aspect of the double-slit experiment. This also appears to support the arguments of quantum physicists, namely, that observing the wavefunction will cause it to collapse.

4. The quantum eraser experiment—Quantum physicists argue the double-slit experiment demonstrates another unusual property of quantum mechanics, namely, an effect termed the quantum eraser experiment. Essentially, it has two parts:

a. Detectors record the path of a photon regarding which slit it goes through. As described above, the act of measuring “which path” destroys the interference pattern.
b. If the “which path” information is erased, the interference pattern returns. It does not matter in which order the “which path” information is erased. It can be erased before or after the detection of the photons.

This appears to support the wavefunction collapse theory, namely, observing the photon causes its wavefunction to collapse and assume a single value.

5. If the detector replaces the screen and only views the atoms or photons after they have passed through the slits, once again, the interference pattern vanishes and we get only two slits of light or atoms. How can we explain this? In 1978, American theoretical physicist John Wheeler (1911–2008) proposed that observing the photon or atom after it passes through the slit would ultimately determine if the photon or atom acts like a wave or particle. If you attempt to observe the photon or atom, or in any way collect data regarding either one’s behavior, the interference pattern vanishes, and you only get two slits of photons or atoms. In 1984, Carroll Alley, Oleg Jakubowicz, and William Wickes proved this experimentally at the University of Maryland. This is the “delayed-choice experiment.” Somehow, in measuring the future state of the photon, the results were able to influence their behavior at the slits. In effect, we are twisting the arrow of time, causing the future to influence the past. Numerous additional experiments confirm this result.

Let us pause here and be perfectly clear. Measuring the future state of the photon after it has gone through the slits causes the interference pattern to vanish. Somehow, a measurement in the future is able to reach back into the past and cause the photons to behave differently. In this case, the measurement of the photon causes its wave nature to vanish (i.e., collapse) even after it has gone through the slit. The photon now acts like a particle, not a wave. This paradox is clear evidence that a future action can reach back and change the past.

Summary

The above experimental results raise questions about the “arrow of time.” It appears that under certain circumstances, the arrow of time can point in either direction, and time can flow in either direction, forward or backward. This is a scientific result. It may be hard to believe, but the above experiments have been repeated. In the case of the double-slit experiment, it has been repeated numerous times. No one has been able to provide a widely accepted explanation. Reverse causality is a true mystery of science.

 

A colorful simulation of cosmic web structure showing galaxies and dark matter distribution in the universe.

A Vacuum is Filled with Energy

Categories, Physics, Universe Mysteries, , ,

Most people think that a vacuum is empty, but it is not. It is filled with energy. This may be hard to believe, but it is a scientific fact.

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. Let’s understand these points.

  • What is the Heisenberg uncertainty principle? 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.

Therefore, a vacuum is not empty. It is filled with energy.

A view of Earth and the Moon against the blackness of space, showing Earth's blue oceans and white clouds.

Why is Earth’s Moon Leaving Us?

Categories, Physics, Threats to Humankind, Universe Mysteries, , ,

Most people don’t know this scientific fact, but the Earth’s Moon is slowing moving further from the Earth. Each year its orbit around the earth experiences a mean recession rate of 2.16 cm/year (less than an inch, since approximately 2.5 cm = 1 inch).

What causes this? As the moon’s gravity pulls on the Earth, the Earth’s gravity pulls on the moon, making the Moon slightly egg-shaped. In addition, tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon’s orbit, making the Moon’s orbit bigger and slower. Thus, not only is the orbit of the moon getting bigger, it is slowing down. Another startling fact is that the Earth’s rotation is slowing down because of the energy lost to the Moon’s orbit.

How real is this effect? To answer this question, let us consider how the Earth’s Moon was formed. Most astrophysicists contend the Moon was formed when a  proto-planet (named Theia after a Greek goddess) about the size of Mars collided with the Earth around 4.5 billion years ago. After the collision, the debris left over from the impact coalesced to form the Moon. Initially, our newly formed Moon orbited the Earth at 22,500 km (14,000 miles) away, compared with 402,336 km (~250,000 miles)  today.

This theory, regarding the Moon’s formulation and gradual recession from the Earth, has been mathematically modeled. Computer simulations of such an impact are consistent with the Earth Moon system we currently observe. There is also physical evidence. Paleontological evidence  of tidal rhythmites, also known as tidally laminated sediments, confirms the above theory. 

What is this going to mean to us on Earth? The speed at which the Moon is moving away from Earth will eventually affect life on the planet, but it will take billions of years for the effect to become significant. Given that Archaic Homo sapiens, the forerunner of anatomically modern humans, evolved between 400,000 and 250,000 years ago, and our progress from cave dwellers to space adventurers during our existence on Earth, it is likely we will have colonized new Earths long before the Moon’s orbit threatens our existence.

There are numerous scholarly papers that delineate the mathematics and palentological evidence in detail. However, they all come to essentially the same conclusion. The Moon is moving further away from the Earth each year.

Close-up of an ornate astronomical clock with zodiac signs and intricate golden details.

Five Facts about Time

Categories, Physics, ,

Here are some interesting facts to ponder about of time:

  1. There is no widely accepted scientific definition of time as a stand alone entity. The reason for this is that according the Einstein’s theory of relativity, time and space are integrated into space-time.
  2. Some physicists argue that “time” has not always existed. According to the big bang theory, the universe started as an infinitely dense small energy ball that expanded to create the universe we now observe. Since some physicist argue that time is a measure of change, before the big bang, there was no change. Hence, there was no time.
  3. Time as measured by clocks will actually slow down in a reference frame moving close to the speed of light or in a high gravitational field. This has been experimentally proven.
  4. Time on Earth is slowing down. Our human perception of time comes from the rotation of the Earth relative to the Sun. Due to tidal friction from the sun and moon, the solar day is lengthening by 1.7 milliseconds each century as the Earth’s rotation slows down.
  5. Your significant other has their own definition of time. It is called a “jiffy.” The jiffy is an undefined time interval that can mean a faction of second to an hour or more. They generally use it in the phrase, “I’ll be ready in a jiffy.”  🙂
A bright meteor streaks across the night sky above Earth, illuminating the atmosphere and ocean below.

Is There Life on Another Earth-Like Planet?

Categories, Life, Physics, Universe Mysteries, , , , ,

Let’s start our discussion by asking a simple question. Is there another Earth-like planet? The answer is yes, and it is relatively close, by galactic standards. In my book, Unraveling the Universes Mysteries (2012), I mentioned the first Earth-like planet discovered, Kepler 22b. Kepler 22b is, to the best of our scientific measurements, Earth-like. Perhaps when our grandchildren’s grandchildren read this book or one like it, it will be old hat. We will have discovered countless Earth-like planets, and perhaps our grandchildren’s grandchildren will be living on one of them.

If it is Earth-like, will it have life on it? The odds are it will. Hard to believe? It will become more believable if we examine how life spreads around in the universe. To understand this phenomenon, we will start with our own planet, which we know had life on it when the dinosaurs became extinct 65 million years ago.

From the fossil record, the extinction of the dinosaurs most likely occurred when an asteroid, approximately 10 km in diameter (about six miles wide), and weighing more than a trillion tons, hit Earth. The impact killed all surface life in its vicinity, and covered the Earth with super-heated ash clouds. Eventually, those clouds spelled doom for most life on the Earth’s surface. However, this sounds like the end of life, not the beginning. It was the end of life for numerous species on Earth, like the dinosaurs. However, the asteroid impact did one other incredible thing. It ejected billions of tons of earth and water into space. Locked within the earth and water—was life. The asteroid’s impact launched life-bearing material into space. Consider this a form of cosmic seeding, similar to the way winds on Earth carry seeds to other locations to spread life.

Where did all this life-bearing earth and water go? A scientific paper from Tetsuya Hara and colleagues, Kyoto Sangyo University in Japan, (Transfer of Life-Bearing Meteorites from Earth to Other Planets, Journal of Cosmology, 2010, Vol 7, 1731-1742), provide an insightful answer to our question. Their estimate is that the ejected material spread throughout a significant portion of the galaxy. Of course, a substantial amount of material is going to end up on the Moon, Mars, and other planets close to us. However, the surprising part is that they calculate that a significant portion of the material landed on the Jovian moon Europa, the Saturnian moon Enceladus, and even Earth-like exoplanets. It is even possible that a portion of the ejected material landed on a comet, which in turn took it for a cosmic ride throughout the galaxy. If any life forms within the material survived the relatively short journey to any of the moons and planets in our own solar system, the survivors would have had over 64 million years to germinate and evolve.

Would the life forms survive an interstellar journey? No one knows. Here, though, are incredible facts about seeds. The United States National Center for Genetic Resources Preservation has stored seeds, dry and frozen, for over forty years. They claim that the seeds are still viable, and will germinate under the right conditions. The temperature in space, absent a heat source like a star, is extremely cold. Let me be clear on this point. Space itself has no temperature. Objects in space have a temperature due to their proximity to an energy source. The cosmic microwave background, the farthest-away entity we can see in space, is about 3 degrees Kelvin. The Kelvin temperature scale is often used in science, since 0 degrees Kelvin represents the total absence of heat energy. The Kelvin temperature scale can be converted to the more familiar Fahrenheit temperature scale, as illustrated in the following. An isolated thermometer, light years from the cosmic microwave background, would likely cool to a couple of degrees above Kelvin. Water freezes at 273 degrees Kelvin, which, for reference, is equivalent to 32 degrees Fahrenheit. Once the material escapes our solar system, expect it to become cold to the point of freezing. If the material landed on a comet, the life forms could have gone into hibernation, at whatever temperature exists on the comet. If an object in space passes close to radiation (such as sunlight), its temperature can soar hundreds of degrees Kelvin. Water boils at 373 degrees Kelvin, which is equivalent to 212 degrees Fahrenheit. We have no idea how long life-bearing material could survive in such conditions. However, our study of life in Earth’s most extreme environments demonstrates that life, like Pompeii worms that live at temperatures 176 degrees Fahrenheit, is highly adaptable. We know that forms of life, lichens, found in Earth’s most extreme environments, are capable of surviving on Mars. This was experimentally proven by using the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center. It is even possible that the Earth itself was seeded via interstellar material from another planet. Our galaxy is ten billion years old. Dr. Hara and colleagues estimate that if life formed on a planet in our galaxy when it was extremely young, an asteroid’s impact on such a planet could have seeded the Earth about 4.6 billion years ago.

Would any of the life-bearing material be able to reach Kepler 22b? The trip to Kepler 22b would have taken an Earth meteorite about 30 million years to reach it. However, the amount of material reaching Kepler 22b would likely be small, due to dispersion. To understand dispersion, consider a flashlight. If you shine the light on a nearby wall, you will see a bright spot on the wall. This is due to the high number of photons that concentrate on the wall to form the bright spot. However, if you move farther away from the wall, the bright spot becomes larger and dimmer. The photons are spreading over a larger area, and are not as concentrated. If you move back far enough, the bright spot will eventually fade, and only a faint glow will be seen on the wall. This phenomenon is called dispersion. The photons being emitted from the flashlight spread apart and become less dense the farther they travel from the flashlight. This same phenomenon occurred when the dinosaur-killing asteroid ejected material from the Earth. As it traveled farther from the Earth, the ejected material began to spread further apart (disperse). Even if a portion of life-bearing material made it to Kepler 22b, the smaller meteorites may have simply burned up in its atmosphere. This is what happens on Earth. Since Kepler 22b is twice the diameter of Earth, it is likely to have a dense atmosphere. Yet, the possibility of seeding Kepler 22b with Earth’s life-bearing material is still possible. If it happened, the life forms would have had 35 million years to evolve.

This is essentially a new way of thinking about the origin of life on Earth, and on other planets. This process of spreading life between planets is known as the panspermia theory of life. Once life forms on a planet, it appears that the cosmos itself takes care of spreading it throughout the galaxy. Therefore, you may begin to conclude that life on other planets would look a lot like life on Earth. That would be unlikely, unless the planet closely resembled Earth. As we see when we study life in extreme environments on Earth, life adapts to the environment. Therefore, on a large planet where gravity might be three times greater than on Earth, the life forms would have evolved to accommodate the increased gravity. Perhaps they would be closer to the ground, and have larger legs or even no legs, like snakes. Perhaps they have larger eyes if the planet has low light. Perhaps they have no eyes, like worms, if the planet is in darkness. Science fiction writers do an excellent job of conjuring up extraterrestrial life based on the planet from which the life forms originate. You can use your imagination to draw your own conclusions on what they might look like, based on their planet of origin.