1) What Is Gravity Really?
We all know that gravity attracts one mass to another, but how exactly does it do that? No one really knows, but also, nobody denies that gravity exists. We just do not understand how it works. Newton's equations accurately describe gravity events here on earth. Einstein's equations accurately describe celestial events extremely accurately. Newton's equations are a simplified version of Einstein's equations, so there is no conflict between them. Bottom line - Einstein describes outer space events very well while Newton takes care of normal events (as opposed to atomic events) here on earth.
But no one can describe exactly "how" gravity works. What exactly is the mechanism that makes a rock sink to the bottom of a pool? How do stars bend light rays coming around them? Is Einstein's explanation of a curved space-time correct? See the picture to the left of the famous Steven Hawkings weightless in a very special jet during a dive that leaves passengers weightless for a short period of time. Exactly how is he lifted into weightlessness?
A popular theory is that there are gravitons, tiny massless force particles, that move back and forth between all matter and that attract each other in a gravitational field. Gravitons are extremely weak on a local scale yet extremely strong on a celestial scale. While this theory has a high intellectual appeal, after hundreds years of observation and experimentation, there is no concrete evidence that gravitons exist. Most scientists have lost faith in the reality of gravitons, but no one has a better explanation.
When Einstein introduced his General Relativity Theory in 1915, many scientists were skeptical that the sun could bend light traveling around it because light photons had no mass. According to Newton, objects with mass attracted each other, but by 1915 most scientists believed light photons had zero mass. When in 1919 Einstein was proved correct, scientists were truly amazed. Einstein explained that there was a curve in space-time around large objects like the earth and sun. See the sketch to the left. But, when a rock sinks in water, is there such a thing as a curve in water-time? Is water just a denser form of space-time? Both Newton and Einstein describe extremely well "what" gravity does, but not "how" it works. Newton until he died was very disturbed that he could not explain "how"gravity worked.
Physics is currently divided into two different worlds. One is Einstein's world of large objects governed by his set of field equations and gravity. The other world is one of micro atomic phenomenon called Quantum Mechanics which excludes gravity. Both theories have extensive histories of precise experimentation that have successfully predicted outcomes to many decimal places. Although many people have tried to combine these two theories into one "grand" theory of everything, to date no one has been able to do so.
Some Quantum enthusiasts have gone so far as to suggest that gravity may not be a fundamental force at all. It may be the offspring of the three known fundamental forces acting in some unknown way with space and time. (This seems a bit far fetched to most scientific people.) On the other hand, string theorists have been able to incorporate gravity into their mathematical theory, but there is no evidence that String Theory as a whole is correct. However, many scientists believe that String Theory will eventually evolve into the "grand" theory that all scientists are looking for.
Dr. Erik Verlinde is a respected Professor of Physics and String Theory at the University of Amsterdam and was previously at Princeton. He published a paper in 2010 and has given lectures that challenge the historical view of gravity. Verlinde suggests that gravity is somewhat like temperature. What exactly is temperature? Temperature per se does not exist. Temperature is the statistical average energy of billions of molecules in a given volume. Similarly, Verlinde suggests that gravity is the "average attraction" of one set of zillions of molecules in a given region attracting another set of zillions of molecules. In other words gravity is not a large systems phenomenon but the combined contribution of many tiny individual molecules attracting one another per an unknown rule of Quantum Physics. Such a new Quantum rule would not obsolete either Newton or Einstein theories, their equations would simply be demoted to effective field equations. Verlinde's reasoning has caused many scientists to take a hard look at gravity on a molecular basis. Currently, Quantum Mechanics does not address gravity, but almost all scientists believe that one day it will. Verlinde has set the stage for a brand new theory of gravity. See a short gravity video by Erik Verlinde here.
In a new paper, which appeared in November 2016 on the ArXiv preprint server, Verlinde shows how his theory of gravity accurately predicts the velocities by which stars rotate around the center of the Milky Way, as well as the motion of stars inside other galaxies. Also, a team led by astronomer Margot Brouwer at the Leiden Observatory, The Netherlands measured the distribution of gravity around more than 33,000 galaxies to put Verlinde's prediction to the test. She concluded that Verlinde's theory agrees well with the measured gravity distribution, but she emphasizes that dark matter could also explain the extra gravitational forces. However, the mass of dark matter is a "free parameter", which must be adjusted for each observation. But, Verlinde's theory provides a direct prediction, without any free parameters. A Verlinde limitation is that the new theory is currently only applicable to isolated, spherical and static systems, while the universe is dynamic and complex. Many real observations cannot yet be explained by the new theory, so dark matter is still in the game. Top
2) What The Heck Is Quantum Entanglement?
When a pair or group of particles can only be described with one quantum state for the whole group, and not as a collection of smaller quantum states, the particles are said to be "entangled". Entanglement between small particles happens as they push and pull on each other, even though each particle has a lot of information about the other, they do not send messages back and forth. However, the particles are always connected and behave as one. In the artist's image to the left, the two particles in front are "entangled" with the two particles in the rear, but are not in any way connected. Yet, information from the rear set affects the set in front. Is this a mystery or what?
The concept of entanglement was first put under the scientific spotlight in May of 1935, when a paper by Einstein and two associates appeared in the journal Physical Review. The paper left no doubt that it was a challenge to Niels Bohr and his vision of the subatomic world of Quantum Mechanics. Einstein called it "spooky action at a distance" which is a translation of his actual words in German. He wrote this because he did not believe that quantum particles could affect one another faster than the speed of light. Einstein believed that entanglement was proof that Quantum Theory at that time was incomplete and needed major revisions.
Suppose you have two particles, A and B, which are connected through quantum entanglement, then the properties of A and B are correlated. For example, the spin of A may be 1/2 and the spin of B may be -1/2, or vice versa. Quantum physics says that until a measurement is made, these particles are in a "superposition" of possible states. That is, the spin of A is "both" 1/2 and -1/2. (See the article on Schroedinger's Cat.) However, once you measure the spin of A, you know for sure the value of B's spin without ever having to measure it directly. If A has spin 1/2, then B's spin has to be -1/2. If A has spin -1/2, then B's spin has to be 1/2. The question at the heart of entanglement is: How does the information get communicated from particle A to particle B? This is the great "entanglement mystery".
In 1964 John Stuart Bell, a talented Irish physicist who worked at CERN, proposed a number of experiments designed to test the validity of entanglement. His tests have come to be called Bell's Theorem. Bell's tests confirmed entanglement and since then many other tests have been performed, all of which confirm Bell's Theorem and the validity of entanglement and Quantum Mechanics.
A recent test by a Chinese group of physicists was to create a pair of entangled particle photons and separate them by a distance of 15.3 kilometers (9.5 miles). The experiment involved a measurement of one photon and then timing how long it took for the other photon to be influenced. To gain sufficient data, the experiment was run continuously for 12 hours. Based on this data, an estimated minimum speed of 3 trillion metres per second, or 10,000 times the speed of light, was determined. The scientists are quite firm that this is just the "minimum speed", which was limited by their ability to measure the extremely high speeds involved. The real speed is probably infinity.
In the latest proposed distance test, here on earth European researchers would “entangle” a pair of photons and then send one of the photons up to the International Space Station (ISS) and into a detector. See the artist's illustration at the left. By examining one photon of the pair on earth and one on the ISS, scientists would be able to test the properties of quantum entanglement between particles separated by roughly 250 miles. If the photons were found to affect one another instantly across 250 miles, it would be a new record. (Previous tests have been done up to 155 miles.) It would also allow scientists to determine whether gravity has any effect on entanglement. Top
3) Dark Matter
What Evidence Is There For Dark Matter?
Dark matter is one of the biggest mysteries of modern physics. The first person to provide evidence of the presence of dark matter was astro-physicist Fritz Zwicky of Caltech in 1933. Zwicky estimated the total mass of the Coma Cluster of Galaxies based on the speed of the galaxies near its edge. He then compared that estimate to one based on the number of galaxies in the cluster. He found there was about 400 times more estimated mass than was observable. Zwicky inferred that there must be some non-visible form of matter (now called dark matter) which would provide enough mass, and therefore gravity, to hold the cluster together.
In 1975 Vera Rubin, a young female astronomer at the Department of Terrestrial Magnetism in Washington, DC, announced that based on her spectrographic data, most stars in spiral galaxies orbit at roughly the same speed. This implied that their masses were the same. These results suggested that either Newtonian Gravity does not apply universally or that more than 50% of the mass of these galaxies was dark matter. Met with much skepticism, Rubin insisted that her observations were correct. Eventually other astronomers corroborated her work and it became accepted that most galaxies were in fact dominated by "dark matter".
The image to the left is known as the Ring Of Dark Matter in the galaxy cluster Cl 0024+17. The light blue ring map of the cluster's dark matter distribution is superimposed on a Hubble image of the cluster. This Ring is one of the strongest pieces of evidence for the existence of dark matter, an unknown substance that permeates the universe.
The galaxy in the picture to the left is known as the Bullet Cluster, so named because of the red bullet shaped pocket of gas on the right side. The light blue halos (clumps) are believed to be dark matter and the red halos are hot gases. The Bullet Cluster is actually two clusters of galaxies having collided with one another. As the two clusters crossed (at a speed of about 10 million miles per hour), the luminous matter (red halos) in each cluster interacted with the luminous matter in the other cluster, causing both of them to slow down.
But the dark matter (blue halos) in each cluster did not interact at all, passing right through without disruption. This difference in interaction caused the dark matter (blue halos) to speed ahead of the luminous matter (the red gas halos), separating each cluster into two components: dark matter in the lead and luminous matter lagging behind. Most astro-physicists consider the Bullet Cluster to be the most compelling evidence that dark matter really exists and demonstrates dark matter's exotic behavior.
Dark matter is particularly elusive as it does not emit, absorb or reflect light, but makes itself apparent only through gravitational attraction. If asked what dark matter is, most scientists in the field will honestly respond that they do not know.
However, we "do" know from WMAP satellite data, that ordinary matter (made up of atoms) makes up only 4.6% of the universe (to within 0.1%). That "dark matter" (not made up of atoms) makes up 23.3% (to within 1.3%). And, that "dark energy" makes up 72.1% of the universe (to within 1.5%). So there is five times as much dark matter in the universe as there is ordinary matter if Einstein's gravity equations are true. And, there is overwhelming evidence that they are true. There does not appear to be any alternative scientific explanation that can explain dark matter on all scales, so the conclusion that dark matter exists appears unavoidable. Top
What Might Dark Matter Consist Of?
Shown in the photo at the left, taken by the Subaru Telescope in Hawaii, are 18 galaxy clusters. Each cluster contains thousands of galaxies with giant halos (clumps) of dark matter (shown in blue) inferred with the help of gravitational lensing. All the halos are flattened a bit like footballs, with their horizontal axes about twice as long as the vertical axes, regardless of the shape and distribution of their galaxy clusters.
In general, dark matter may be like ordinary matter but in some form which makes it invisible, or else it may be some exotic form of non-ordinary matter. Hypothetical normal dark matter objects are usually referred to as MACHOs - massive compact halo objects - since they are candidates for explaining dark matter within galaxy clusters.
On the other hand, dark matter may be non-ordinary matter. Hypothetical favorites among non-ordinary dark matter contenders are weakly interacting massive particles (WIMPs), predicted by supersymmetry particle theories, and axions, predicted by other promising theories.
Theoretical calculations of the amount of small mass elements formed in the early Big Bang universe indicate that the total amount of ordinary matter can be no more than ten times the amount of visible matter. This is sufficient to explain the amount of ordinary dark matter on the scale of galaxies but not enough to explain the amount of dark matter in galaxy clusters. Therefore, the existence of non-ordinary dark matter appears inescapable. However to date, no particles with invisible mass, with light able to pass through them, with gravitational pull, and with zero radiation characteristics have been discovered. Top
Weakly Interacting Massive Particles (WIMPs) are part of a hypothetical class of new particles that emerge from supersymmetry theory. Supersymmetry theory is a theory where known elementary particles have supersymmetric partner particles. The theory suggests that every fundamental matter particle has a massive shadow "force" carrier particle, and every force carrier particle has a massive shadow "matter" particle. For example, an electron has a "selectron' for a partner, a quark has a "squark".
On very rare occasion, a dark matter particle might just collide with a normal matter atom. The trick is to catch that signal amid the storm of outer space particles bombarding the earth so thickly that hundreds pass through our bodies each second. Nearly a mile underground in South Dakota, the ultra-sensitive Large Underground Xenon experiment, or LUX, is searching for evidence of dark matter. LUX is the latest of several experiments trying to discover dark matter. LUX, with a two story state of the art detector, shown at the left, is sheltered in what was once North America's deepest gold mine. Scientists are looking for a flash of something far more elusive than gold - dark matter.
Scientists utilize caverns deep inside the earth to mute the outer space particle bombardment that surrounds us. The LUX tank is filled with liquid xenon that is extremely dense and is surrounded by a 70,000 gallon shield of water. Scientists then wait for dark matter particles to hit it. Xenon is so chemically inert that electron signals from any collisions can pass freely through the liquid. These crucial signals allow scientists to eliminate noise from a true dark matter signal. Scientists will watch for a two-flash combination to occur when a dark matter particle collides with the highly purified xenon inside the detector. LUX is estimated to be at least 10 times more sensitive than all previous detectors.
Since running the detector from August, 2013 and looking for tiny flashes of light that could indicate a dark matter particle collision, LUX researchers have found no signals beyond the background noise. However, they did so at far greater sensitivities than any previous experiment and the watching continues.
In addition to LUX, experiments at the Large Hadron Collider (LHC) in CERN have also been looking for supersymmetry particles as part of their experiments using high energy collisions. Supersymmetry dark matter particles should annihilate in a very particular way which up until now have not been detected. Neither have any other light mass supersymmetry particles been detected. As of December, 2013, the data from both the Atlas and CMS detectors have ruled out supersymmetric particles up to about a thousand times the mass of a photon, a pretty hefty size. No final conclusions can be drawn until the advent of the LHC upgrade to 14 TeV (from 8 TeV) collisions that will start in 2015. However, many scientists feel that if supersymmetry exists, the lighter particles should have been seen by now. Since WIMPs are part of supersymmetry theory, confidence that WIMPs exist has also been shaken. Top
Axions are "hypothetical" tiny, tiny particles that have a mass about 500 million times lighter than an electron. Additionally, an axion has no spin, is electrically neutral, and interacts very weakly with other particles. However, axions do react gravitationally with other matter. Axion particles were originally suggested in 1977 to solve a complex problem in advanced quantum theory. However, axions have never been experimentally detected and remain purely theoretical particles. If axions do exist, zillions would have been produced just after the Big Bang and the universe should be full of them.
If the axion is as light as believed and interacts so weakly that it is nearly impossible to detect, that makes it an ideal dark matter candidate. The goal of the ADMX (Axion Dark Matter eXperiment) at the University of Washington, pictured at the left, is to detect this extraordinary small particle.
The Large Hadron Collider (LHC) at CERN, widely known for its discovery of the Higgs boson in 2012, has not yet found any evidence to support supersymmetry. LCH evidence of small mass particles from supersymmetry theory (which was expected) would have given WIMPs a boost as a dark matter candidate. This lack of supersymmetry evidence has prompted scientists to separate the search for dark matter from the search for supersymmetry. Therefore, the newest version of the ADMX is drawing substantial interest from dark matter researchers.
The aim of the Axion Dark Matter Experiment is to detect axions raining down from outer space by sensing the conversion of some axions into photons (light). The detector employs a powerful magnet surrounding a sensitive microwave receiver that is supercooled to about minus 452°F. This low temperature reduces noise and greatly increases the chance that the detector will see some axions converted to photons. The microwave receiver can be fine tuned to the mass of an axion, which also increases the possibility of detecting an axion. A "hit" will produce a very small amount of power in the receiver, which will then be recorded by the attached computers. ADMX was completed in October, 2013. The team has since begun months of testing and fine tuning the equipment before starting the hunt in earnest. For more information on ADMX and Axions visit the University Of Washington web site. Top
4) Dark Energy
Is Dark Energy Real?
When it was discovered in 1998 that the expansion of the universe was accelerating, there was no known force that could be responsible other than resurrecting Einstein's Cosmological Constant. Since a constant isn't a force, "dark energy" was the name given to the unknown force that is believed to be driving galaxies away from each other against the pull of gravity. Nothing comes close to the description of dark energy in the "Standard Model" of fundamental particles and forces developed by quantum physicists.
Dark energy has not yet been detected directly and has properties unlike anything we know. Dark energy is like an anti-gravity force, but since energy and mass are equivalent, there has to be a lot of it in the universe. While gravity pulls things together at the local level, dark energy pushes them apart on a grand scale. Its existence isn't proven, but dark energy is the best guess of most scientists to explain the acceleration of the universe. After a two-year study, scientists at the University of Portsmouth in the United Kingdom and LMU University Munich in Germany have concluded that the likelihood of dark energy's existence stands at 99.996 percent.
Results from the Galaxy Evolution eXplorer (GALEX) Survey Project along with data from the Anglo-Australian Telescope atop Siding Spring Mountain in Australia, confirm the theory that dark energy is a smooth uniform force "all across the universe" that dominates the effects of gravity. It also rules out a dark energy gravity theory which suggested that at large distances gravity reverses its role and becomes repulsive. Above is an artist's representation of how dark energy dominates gravity and space-time. Dark energy is represented by the uniform purple grid, galaxies by the white clusters, while gravity and space-time are represented by the green grid. Top
What Do We "Know" About Dark Energy?
We know that "dark energy" makes up 72.1% of the universe (to within 1.5%). We also know that that the universe's expansion rate was initially decreasing but started to increase at an accelerated rate about 6 billion years ago when the universe was about 8 billion years old. It started accelerating because as the universe expanded, the limited amount of matter in it also expanded. Therefore, the average density of matter decreased, and thus the strength of overall gravity weakened because it depends on the density of matter.
On the other hand, dark energy is presumed to have expanded as space expanded because dark energy is thought to be an intrinsic element of space itself. When the universe reached about 8 billion years of age, the density of dark energy exceeded the density of matter. As a result, the excess dark energy pressure caused the universe to begin to expand in an accelerated fashion. This is the main thesis of dark energy theory that today most physicists believe to be true.
The Caltech GALAX Survey (2006 to 2011) of 200,000 galaxies, stretching back seven billion years in cosmic time, has led to an independent confirmation of the SDSS/BOSS Survey that dark energy is driving our universe apart at accelerating speeds. See the universe expansion curve at the left.
"Sound waves" from the very early universe have left imprints in the locations of galaxies, causing galactic pairs to be nominally separated by approximately 500 million light years. These observations are a result of careful measurements of the separations between many, many pairs of galaxies. The gravitational pull of a galaxy cluster attracts other galaxies locally, but dark energy pushes them apart on a larger cosmic scale. Physicists are able to statistically average the dark energy's repulsive force measured over thousands of pairs of galaxies. See the SDSS/BOSS Survey section for a more detailed explanation of "sound wave imprints".
The GALAX findings offer additional support for the favored theory of how dark energy works - a constant force, uniformly affecting the whole universe and propelling its accelerated expansion. The amount of dark energy in the universe and its repulsive force is basically all we know for sure about dark energy. Top
Dark Energy Hypotheses:
Dark Energy Is Part Of Space Itself
This dominant theory says that "empty space" is not really empty. We know space bends and curves around large objects as in gravitational lensing. In addition, it apparently has its own inherit energy. This theory is embedded in Einstein's General Relativity equations. His original equations implied the universe was either expanding or contracting but not in a "steady state" (i.e. static). Einstein recognized this and it bothered him that his equations allowed the universe to contract, as he believed at the time that it was static. So he arbitrarily introduced a "cosmological constant" (noted as the Greek capital letter Lambda "Λ") into his equations to prevent the universe from either collapsing or accelerating, but to remain static.
Einstein's original equations did allow for more space to continuously come into existence (i.e. universe expansion) if the cosmological constant was zero. In 1929, Hubble in fact showed that the universe was actually expanding and it forced Einstein to remove his constant calling it the "biggest mistake of my life". This does not mean that space is expanding into some kind of vacuum. It means that space-time itself is growing, which means that more dark energy is also growing. As a result, this form of energy, as it grew and overcame a constant amount of gravity, eventually caused the universe to expand faster and faster. With the discovery of accelerated expansion in 1998, scientists had to re-enter "Λ" back into the equations, but this time for a different purpose. If the force of gravity is considered a positive force as it pulls things together, then the cosmological constant is a negative force as it repulses gravity. They called "Λ" dark energy for lack of a better name for an unknown force. Currently some scientists refer to this force as "negative energy" or "vacuum energy" because it it is more descriptive, but the most popular term remains "dark energy". Unfortunately, no one understands why "Λ" should "theoretically" be included in the equations, much less why it should have exactly the right value to match the observed acceleration. It is now included based on purely empirical evidence which is very acceptable as science needs to reflect reality. This is the most popular dark energy theory and is generally accepted by most physicists. Top
Quantum Vacuum Energy
Another possible explanation for how space might acquire energy comes from the "quantum theory" of matter. In quantum theory, empty space is not empty at all, but is full of energy in the form of invisible electro-magnetic waves. These waves fluctuate wildly, continuously forming temporary "virtual" particles (particle/antiparticle pairs) that then immediately annihilate each other and electrically cancel out in a time span too short to measure. (Hence our human perception of an empty vacuum.) However, the average vacuum energy is not zero, but a minimum quantity, called the "zero point" energy or "ground state" energy. Quantum theory also postulates that all particles exhibit wave behavior, so the fact that waves turn into fleeting particles and back again is not anything revolutionary. Some scientists refer to outer space as the "quantum vacuum".
However, when physicists calculate how much "vacuum energy" this would give all of empty space, the answer comes out way too large, 10^120 times larger than currently measured, that is a 10 with 120 zeros after it. No one can accept a theory that is this far off, so this theory as proposed can not be correct. However, almost all current scientists believe that today's quantum theory, while explaining most of matter extremely well, is incomplete because of this vacuum energy issue, the fact that it does not incorporate gravity and some other minor problems. Someday, somehow scientists believe these issues will be rectified by a new version of quantum theory or another completely new theory. So the basic idea of combining quantum theory with dark energy is alive going forward, but on somewhat shaky ground. Top
Acceleration Is An Illusion
Dark Flow. Alexander Kashlinsky is a cosmologist at NASA's Observational Cosmology Laboratory at the Goddard Space Flight Center in Maryland. In a series of papers over the past few years, Kashlinsky and his colleagues have shown that the region of space-time which we occupy, a huge region at least 2.5 billion light years across, is moving fast relative to the rest of the universe. Some cosmologists remain skeptical about this "dark flow," as it is called. They say that more evidence is needed to persuade everyone that this phenomenon is real. But the evidence that does exist is compelling. Based on light collected from galaxy clusters, Kashlinsky says our little region of space-time is moving at 2 million miles per hour relative to our galaxy neighbors.
Acceleration An Illusion. A new theory by Christos Tsagas, a cosmologist at Aristotle University of Thessaloniki in Greece, suggests that the accelerating expansion of the universe is merely an illusion. A false impression results from the way our particular region of the universe is moving through space. His theory says our relative motion makes it look like the universe as a whole is expanding in a accelerated fashion. While in reality, expansion is really slowing down, just as would be expected from ordinary gravity. By not taking into account the dark flow, we get the false impression that the whole of space-time has entered an accelerating phase. If you're swimming in a river with the current, you move faster than when you swim upstream against it. Tsagas argues that this is why we perceive the expansion of space-time as faster in the direction of our motion than any other direction.
Tsagas has also said the "preferred axis" alignment of the CMB with our motion is no mere coincidence. The CMB axis is another illusory effect of the "dark flow" of our space-time bubble. Tsagas explains our observations of the expansion of space-time without invoking dark energy. According to Tsagas, the acceleration of the universe in our immediate vicinity is caused by motion alone. The universe beyond our region isn't accelerating outward. Rather, it is rolling to a stop as predicted by Einstein's equations. Tsagas has shown that the universe either has dark flow or dark energy, but not both. Dark flow is by far the less mysterious of the two. While no one knows exactly what dark energy is, dark flow is just movement. Top
5) Are EmDrives Real?
In 2001, the Electromagnetic Drive (EmDrive, pictured to the left) was initially designed by English aerospace engineer Roger Shawyer (left below). The technology can be summed up as a propellant less propulsion system, meaning the engine doesn’t use fuel to cause a thrust reaction. Removing the need for fuel makes a craft substantially lighter, and therefore easier to move and cheaper to make. In addition, the hypothetical drive is able to reach extremely high speeds. Potentially getting humans to the outer reaches of the solar system in a matter of months.
Critics say that according to Newton's law of conservation of momentum, EmDrive theory cannot work because in order for a thruster to gain momentum in one direction, a propellant must be expelled in the opposite direction. However, the EmDrive is a closed system with nothing being expelled.
Shawyer claims that the EmDrive does in fact preserve the law of conservation of momentum and energy because it follows fundamental classical physics (quantum physics not involved). It bounces microwaves back and forth inside a cone-shaped metal cavity (as pictured above). A magnetron pushes the microwaves against the short end of the cone propelling the craft forward in the direction of the short end. The EmDrive will eventually allow a spacecraft to reach the moon in just four hours, Mars in 70 days, and Pluto in just 18 months.
After recent months of heated debate and leaked documents, NASA's long-awaited EmDrive paper was finally peer-reviewed and published in November of 2016 in the American Institute of Aeronautics and Astronautics' (AIAA) Journal of Propulsion and Power. It confirmed that the EmDrive propulsion system does work. Tests carried out by both NASA and independent researchers verified that the drive was able to produce 1.2 millinewtons per kilowatt of thrust in a vacuum.
The NASA team writes, "If a medium is capable of supporting acoustic oscillations, this means that the internal constituents are capable of interacting and exchanging momentum". NASA continues, "The vacuum is indeed capable of being changed as was done in the experiment. It is possible to extract work from the vacuum and thereby push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum". The next step for the EmDrive is for it to be tested in space, which is scheduled by NASA to happen in the coming months.
Scientists with the China Academy of Space Technology (CAST) claim NASA’s results "re-confirm" what they had already achieved. At a press conference in Beijing, researchers with CAST confirmed the government has been funding research into the EmDrive technology since 2010, and claimed they have developed a device that is already being tested in low-earth orbit.
Many physicists are still non-believers thinking that eventually an error will be found somewhere in the experiment proving that Newton's law for the conservation of momentum is dominant. More experiments are being planned so stay tuned.
String Theory has become quite popular among physicists because it incorporates gravity as well as the other fundamental forces. It contains no infinities and its mathematics is consistent (it all ties together nicely). Unfortunately, string theory has not yet succeeded in producing a set of conditions that correspond to the real world we live in, so it remains just a theory.
In combination with the idea of "inflation" from the Big Bang Theory, some strains of string theory have evolved containing the concept of multiverses. Multiverses suggest that there are many universes that have developed from inflationary bubbles that are different from our own Big Bang. In other words, our universe is not unique, it is just one of many universe bubbles that have evolved over time.
Universe bubble inflation according to some versions of string theory is a chaotic event in a world of many universes. Each bubble develops into a small or big universe completely independent of one another. Events that happen in one bubble cannot be observed in other bubbles. Each bubble appears as a whole universe all to itself. The assembly of all these universes has come to be called the “multiverse.”
As illustrated in the time map to the left, the "observable universe" is the light triangular area in the middle. The total width of the illustration represents our universe as a whole. We can only see and observe events within the triangle because we are limited by the speed of light which is a fixed constant. As time expands so does our field of vision, but so does the unobservable region. If one could rotate the illustration 360 degrees, the internal triangle would form a cone that would determine all that anyone could ever observe no matter what is beyond the cone.
Scientists, such as Leonard Susskind from Stanford, believe that the whole universe is at least 1,000 times greater than the observed universe. This means that there is much, much more to our own universe that we can never know about considering the limited amount we can observe.
There are even mysteries in our "observed" universe that we do not understand. One that immediately comes to mind is the "dark flow" of a huge bunch of galaxies (including our Milky Way) towards what is called "The Great Attractor". See the image below. The Attractor is a region of our visible universe about 650 million light years from the earth in the vicinity of the Shapley Supercluster behind Abel 3565. Galaxies from all directions seem to be traveling at very high velocities (speeds of about 2 million miles per hour) towards this destination. See The Great Attractor & Shapley Supercluster for more information.
However, it is not clear that the Shapley Supercluster or any other known source of gravity is big enough to cause such a huge dark flow towards The Great Attractor. Some string theorists speculate that perhaps the force that lies behind The Great Attractor comes from a nearby multiverse. The theory is that this nearby multiverse, which might have a super large mass, exerts a gravitational force on the traveling galaxies that we can not detect. While this is pure speculation (and perhaps some day dreaming) it does force one to contemplate the possibilities of some effects from sources beyond our observable universe or from an adjacent universe.
The Big Bang Theory does not address what happened before or at the instant of extreme expansion. The Big Bang addresses only events in micro, micro seconds after the Big Bang. Dr. Eric Verlinde, professor of physics and string theory at the University of Amsterdam and Princeton, says:
"It is illogical to think there was nothing and then it exploded. We use concepts like time and space, but we don’t really understand what this means microscopically. I think we will figure out that what we thought was the Big Bang was actually a different kind of event. Or maybe that we should not think that the universe really began at a particular moment and that there’s another way to describe that. In short, the universe originated from something, not from nothing. There was something there. It has something to do with dark energy and how that is related to dark matter. If we understand the equations for those components of our universe, I think we’ll also have a better understanding of how the universe began. I think it’s all about the interplay between these different forms of energy and matter. The whole idea of an expanding universe that started with a big explosion will change. You need to describe more than just the matter particles. You need to know more about what space/time is. All these things have to come together in order to be able to explain the Big Bang."