BEGINNING OF THE UNIVERSE.
WHAT is the Universe? If it is all existing matter and space considered as a whole - the cosmos, or is it a particular sphere of activity or experience. It cannot be the former, because we cannot prove that there is nothing beyond what we have seen till date. Hence we cannot claim that we see all existing matter and space. Thus, it has to be a particular sphere of activity or experience. In other words, it is a function of space-time. Since Einstein, Spacetime has been fused into one both rightly and wrongly. Rightly because both space and time are infinities and infinities coexist. Hence space and time coexist. They are inseparable like two hemispheres of a cosmic brain, joined to a single entity: space-time. but not as spacetime. Because, like two hemispheres of the brain, they have totally different properties and cannot be one and the same entity. For example, space implies the interval between two objects, which can be either fixed or variable in time. But time implies the interval between two events that are uniform throughout the universe. A second is the same interval both here, as well as in any corner in the universe. Time flows, but there is no proof that space also flows. All observations prove the contrary – space has fixed coordinates, whereas time has no fixed coordinates – it is the same flow everywhere. Thus, time is beyond the confines of space.
CONUNDRUMS RELATING TO SPECIAL RELATIVITY.
Special Relativity has confused most people. A man standing on the platform will see the other on the receding train as shrinking, though the man on the train will not experience so. He will see the man on the platform as shrinking, which is also not true. Thus, SR describes appearance – not reality. Otherwise, the photon should not move. As the length contraction would make its spatial extent zero, which is the synonym for non-existence at here-now.
According to relativity, gravitational mass is always equivalent to the inertial mass. No one knows why there should be two or more mass terms. In principle there is no reason why mi = mg: why should the gravitational charge and the inertial mass be equal? The gravitational mass mg is said to produce and respond to gravitational fields. It is said to supply the mass factor in the inverse square law of gravitation: F=Gm1m2/r2. The inertial mass mi is said to supply the mass factor in
Law: F=ma. If gravitation is proportional to g, say F=kg (because the weight of a particle depends on its
gravitational mass, i.e. mg), and acceleration is given by a, then according to Newton ’s law, ma=kg. Since according to GR, g=a,
combining both we get m=k. Here m is the so-called “inertial mass” and k is the
“gravitational mass”. But the problem is the difference between the values of G
(constant – though it might be changing: doi/10.1103/ PhysRevLett.111.101102)
and g (known to be variable). Alternatively, the inertial mass measures the “inertia”,
while the gravitational mass is the coupling strength to the gravitational
field. The gravitational mass plays the same role as the electric charge for electromagnetic
interactions, the color charge for strong interactions and the particle flavor
for weak interactions. Inertial mass mi
is the mass in Newton ’s
law F=mia. Gravitational
mass mg is the
coupling strength in the Newton ’s
law of gravitation: Fg
= (gm1m2/r2) x mg. Thus, mia = Fg = (gm1m2/r2) x mg.
The quantity gm1m2/r2 is the “gravitational
field” (say G) and mg
is the “gravitational charge”, so that one can write: F x g = mg x G, just like we
write: mi x a = q x
E for the electric field. This has nothing to do with the Brout-Englert-Higgs
Mass is the locked up energy of a body. Essentially, it is the amount of resistance that a physical object has to any change in its motion. This includes the resistance that a body has to acceleration or to directional changes. This type of mass, is called ‘inertial mass’. The EP states that the effect of gravity does not depend on the nature or internal structure of a body. Again, according to the same theory, an object must have infinite kinetic energy when it approaches the speed of light, because light has the limiting velocity. Thus, the object has infinite mass as well. An object has infinite kinetic energy when it approaches the speed of light. Since an object will increase its ‘mass’ as it speeds up. As an object increases in speed, the amount of energy it has also increases. Since mass and energy is treated as exchangeable in relativity, this energy is referred to as ‘increase in mass’. Other objects need an external agency to apply energy to get accelerated. But photons, which move at the limiting velocity, do not require such an external agency. They inherently possess this energy. Hence, they should have infinite mass. This is contrary to evidence.
Gravity does not couple to the “gravitational mass” but rather to the Ricci Tensor, which works only if space-time is flat. Ricci Tensor does not provide a full description in more than three dimensions. Schwarzschild equations for black holes, where space-time is extremely curved, uses the Riemann Tensor. Using Riemann tensor, instead of Ricci tensor to calculate energy momentum tensor in 3+1 dimensions would not lead to any meaningful results, though in most cases, the Riemann Tensor is needed before one can determine the Ricci Tensor. Thus, there is really no relation between “gravitational mass” and “inertial mass”, except in Newtonian physics. This is why photons (with zero inertial mass) are affected by gravity. Only manipulations of the Standard Model (SM) to include classical gravity (field theory in curved spacetime) leads to effects like Hawking radiation and the Unrih effect. This is where gravitation and the SM can hypothetically meet.
When answering a question, one should first determine the framework. If we assume nothing then there can be no answer. However, if we take as given that we are going to formulate theories in terms of Lagrangians then there is essentially only one mass parameter that can appear, i.e., the coefficient of the quadratic term. Thus, whatever mass is there, it is only one mass. The Higgs field clearly modifies the on-shell condition in flat space and general relativity simply says that anyone whose frame is locally flat should reproduce the same result. Thus, the Higgs field appears to modify the gravitational mass. It may also modify the inertial mass by the same amount as can be verified by analyzing some scattering diagrams. However, knowing that we are working within the context of a Lagrangian theory, the fact that inertial and gravitational mass are equal is essentially a foregone conclusion.
Similarly, the idea about an astronaut going to outer space at a very fast rate and coming back younger – is misplaced. When on Earth, the fluids in the human body are distributed unevenly because of gravity. Most fluid pools in the lower extremities, leaving very little fluid in the top of the body. But if we go to space, in the first few weeks most astronauts appear to have a puffy head and skinny legs. The fluid in their bodies redistributes evenly when gravity is not playing a significant role in their biological systems. After some time in orbit, the body adapts to the new distribution of fluids and the astronauts do not appear as puffy – it self-regulates. In the near zero relative gravity of space, muscles are not needed to support the body. Instead of maintaining the usual base of muscle mass needed for life on Earth, astronauts’ bodies tend to get rid of unnecessary tissues. Astronauts have to exercise for two hours a day on the space station to maintain a healthy amount of muscle mass. The exercise also helps prevent bone-density loss. Each month, astronauts could lose up to 1 percent of their bone density if they do not get enough exercise.
According to a report published in the magazine PLOS ONE: DOI: 10.1371/ journal.pone.0106207, there is a large discrepancy between physiological and functional thresholds about which we should be cautious when preparing for exposure to low gravity fields. The strength of gravity required from the physiological threshold for linear acceleration in up and down directions has been estimated to be 15 percent of Earth’s gravity – nearly equal to the Moon’s gravity. The perception of up-down is determined not only by gravity, but also visual information, when available, and assumptions about the orientation of the body. Here on Earth, plants and animals are exposed to the same amount of gravity as human beings. Yet, their body functions as if they are in space – distributing body fluids in an organized manner. If the flow is in the direction of growth; then humans should be reptiles – body mass distributed down like in a fluid. How to explain this?
All our biological functions are powered by heart and lungs that pump blood and oxygen. Once the heart starts beating in the mother’s womb, the process continues perpetually till death. How did the initial heartbeat, which is a sign of consciousness, begin? We measure blood pressure to know the rate and pace at which blood is pumped by the heart. This is a deterministic mechanical process leading to chain reactions throughout the body. Can the operations of organisms be described by physical laws, which are probabilistic? A mechanical replacement of organ is dependent on the adaptability of the host organism. Can it be described by pure mechanics? Can we place a heart in a robot to make it alive? Is it life? Without answering these questions, we cannot claim that an astronaut who moves at a faster pace becomes younger than those who moves slowly.
The GPS shows time dilation not because of relativity, but because of refraction of light while moving through different strata of the atmosphere and outer space, where density fluctuations vary the speed of light.
IS SPACETIME FLUID?
In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress. Fluids are a phase of matter and include liquids, gases and plasmas. ... Liquids form a free surface (that is, a surface not created by the container) while gases do not.
But turns out if you write down the equations for small wiggles in a medium – such as soundwaves in a fluid – then the equations look exactly like those of waves in a curved background.
Yes, that’s right. Sometimes, waves in fluids behave like waves in a curved space-time; they behave like waves in a gravitational field. Fluids, therefore, can be used to simulate gravity. And that’s some awesome news because this correspondence between fluids and gravity allows physicists to study situations that are otherwise experimentally inaccessible; for example, what happens near a black hole horizon or during the rapid expansion of the early universe.
This mathematical relation between fluids and gravity is known as “analog gravity.” That’s “analog” as in “analogy” not as opposed to digital. But it’s not just math. The first gravitational analogies have been created in a laboratory.
Most amazing is the work by Jeff Steinhauer at Technion, Haifa. Steinhauer used a condensate of supercooled atoms that “flows” in a potential of laser beams which simulate the black hole horizon. In his experiment, Steinhauer wanted to test whether black holes emit radiation as Stephen Hawking predicted. The temperature of real, astrophysical, black holes is too small to be measurable. But if Hawking’s calculation is right, then the fluid-analogy of black holes should radiate too.
Black holes trap light behind the “event horizon.” A fluid that simulates a black hole doesn’t trap light; instead it traps the fluid’s soundwaves behind what is called the “acoustic horizon.” Since the fluid analogies of black holes aren’t actually black, Bill Unruh suggested calling them “dumb holes.”
But whether the horizon catches light or sound, Hawking-radiation should be produced regardless, and it should appear in form of fluctuations (in the fluid or quantum matter fields, respectively) that are paired across the horizon.
Of course fluid-analogies are still different from real gravity. Mathematically, the most important difference is that the curved space-time which the fluid mimics has to be designed. It is not, unlike real gravity, an automatic reaction to energy and matter; instead, it is part of the experimental setup. However, this is a problem which, at least in principle, can be overcome with a suitable feedback loop.
The conceptually more revealing difference is that the fluid’s correspondence to a curved space-time breaks down once the experiment starts to resolve the fluid’s atomic structure. Fluids, we know, are made of smaller things. Curved space-time, for all we know at present, isn’t. But how certain are we of this? What if the fluid analogy is more than an analogy? Maybe space-time really behaves like a fluid; maybe it is a fluid. And if so, the experiments with fluid-analogies may reveal how we can find evidence for a substructure of space-time.
Some have pushed the gravity-fluid analogy even further. Gia Dvali from LMU Munich, for example, has proposed that real black holes are condensates of gravitons, the hypothetical quanta of the gravitational field. This simple idea, he claims, explains several features of black holes which have so-far puzzled physicists, notably the question how black holes manage to keep the information that falls into them.
We used to think black holes were almost featureless round spheres. But if they are instead, as Dvali says, condensates of many gravitons, then black holes can take on many slightly different configurations in which information can be stored. Even more interesting, Dvali proposes the analogy could be used to design fluids which are as efficient at storing and distributing information as black holes are. The link between condensed matter and astrophysics, hence, works both ways.
Physicists have looked for evidence of space-time being a medium for some while. For example, by studying light from distant sources, such as gamma-ray bursts, they tried to find out whether space has viscosity or whether it causes dispersion (a running apart of frequencies like in a prism). A new line of research is to search for impurities – “space-time defects” – like crystals have. So far the results have been negative. But the experiments with fluid analogies might point the way forward.
If space-time is made of smaller things, this could solve a major problem: how to describe the quantum behavior of space time. Unlike all the other interactions we know of, gravity is a non-quantum theory. This means it doesn’t fit together with the quantum theories that physicists use for elementary particles. All attempts to quantize gravity so-far have either failed or remained unconfirmed speculations. That space itself isn’t fundamental but made of other things is one way to approach the problem.
ROLE OF GRAVITY.
Gravity is responsible for stuff falling on the ground, as well as for planets moving in the sky. Scientific theories have been proposed to account for these phenomena: Newton’s theory of gravity first and Einstein’s general relativity later. Newton’s gravity is a force that acts instantaneously to pull bodies closer in virtue of their mass. In other words two massive bodies, no matter how distant, feel each other’s presence instantly and tend to get together.
Here now comes evidence. Newton’s theory has been very successful. The theory predicted, for instance, the Halley comet to be seen again in 1758. One may even think that our best scientific theories are definitely proven by experiments - Newton’s theory successfully predicted the return of the Halley comet, therefore Newton’s theory is true. Right? Well, no. It does not logically follow that Newton’s theory is true even if all experiments come out as predicted. It like someone concluding that it is snowing right now by starting with the consideration that if it's snowing then the streets will be covered with snow, and then observing that the streets are now covered with snow. This is unwarranted: it takes snow a very long time to melt, so snow could have fallen earlier in the day. Similarly, the Halley comet return is a good indication of the past success of Newton’s theory, but does not provide any guarantee of its future success.
Indeed, it later turned out that Newton’s theory was false and it was substituted by Einstein’s theory of relativity. Einstein argued that gravity is not a force but rather the effect of the modification of the fabric of space-time due to the presence of material bodies. That is, in empty space a body will go straight, but the presence of another body will bend its trajectory as if it were affected by a pulling force. Even if it is an imprecise analogy, a ball thrown on a bed where a cat is sleeping will not go straight but will rather curve towards the cat. Anyway, we cannot prove beyond any doubt a theory to be true, no matter how successful it is. It is better to say that the theory is confirmed, or more cautiously corroborated, by positive experiments: arguably, we have more reasons to believe a theory with lots of confirmatory instances than one with fewer.
Can we at least prove a theory to be false? Newton’s theory would be proven false if the predicted acceleration of falling bodies were different from the measured one, say. Indeed, Newton’s theory was falsified by experiments: the theory predicted Mercury’s orbit around the Sun would not shift forward, which instead does. Such shift was predicted by Einstein’s theory of general relativity. So, can falsification be definite? Again, no: sometimes old theories do not get replaced even if they have contrary evidence. In this case, experimental refutation of Newton’s theory was not the reason why relativity took the place of Newton’s theory in the physics books. Even if the predictions were wrong, scientists were not ready to consider Newton’s theory to be false and kept using it. After all, is it worth throwing away all the successes of such a powerful, explanatory theory just for such a small discrepancy? It could well be some experimental error. Nonetheless, eventually Newton’s theory was replaced because of theoretical, rather than empirical, reasons. Einstein proposed his theory of relativity because he found the ‘spooky action-at-a-distance’ of Newton’s theory of gravity extremely unsatisfactory. Therefore, he looked for another explanation and he found it. The bonus was that his theory could also correctly recover the shift in Mercury’s orbit that Newton’s theory could not account for.
Also, consider this other example. Gravity keeps the universe together and one of the leading early theories of the origin of the universe is the big bang theory: the universe started expanding after a huge explosion at the beginning of time. One should expect sooner or later the universe to slow down, just like the fragments of a more ‘regular’ explosion. However, recent astronomical data suggest that the fragments are getting away at increasing speed. This is a falsification of the big bang theory, which predicted deceleration. Nonetheless, sometimes, like in the case of Newton’s failure to predict Mercury’s orbital shift, rejecting falsified theories seems just too harsh. If I drop an egg on the floor and it does not break as expected, I will not claim I have refuted the current theory of gravity. Rather, I will check for false assumptions that would explain the mistaken result. Another example is that Newton’s theory predicted a different orbit for Uranus than the one observed. So the theory was, again, falsified. However, instead of rejecting Newton’s theory, astronomers questioned the assumption that there were seven planets: the existence of another planet, Neptune, would explain the observed orbit of Uranus, which they indeed later observed.
Back to the case of the accelerating universe, many astronomers decided to do the same thing: they did not refute the theory, even with contrary evidence. In a sense, they proposed that gravity has its own dark side: something, now known as dark energy, which overpowers gravity’s attraction. More precisely, they questioned the assumption that space-time has no energy in itself. One may think of this as a repulsive gravity or anti-gravity, but do not read too much into it. Notice that hidden, unquestioned, assumptions are everywhere. For instance, when using a microscope, we assume light propagates in a straight line, even if it does not. There are some situations in which this is irrelevant, but some others in which it may not. Hence, when facing empirical refutation, scientists always have the option to put the theory into question or to challenge some hidden assumption instead. In this case, astronomers could either deny the existence of dark energy and radically modify general relativity, or assume dark energy exists without modifying general relativity too much. If the former is the case, there is a sense in which there is anti-gravity; if the latter, there is not. The philosophical question therefore is: when is it reasonable for a scientist to hold on to her theory, and when is she just stubbornly in love with it?
Even if this is not the case here, I am sure you understand the gravity of the situation (pun intended!) if alternative theories are empirically equivalent. That is, in the case in which no experiment can be performed to tell them apart. This happens, for instance, between some different formulations of non-relativistic quantum mechanics. If we cannot choose which theory is correct based on the empirical results, what can help us? It is unclear: some will say super-empirical, or purely theoretical virtues, should be important. Simpler theories, for instance, should be preferred. However, what is simplicity? Why should we believe that the universe is simple?
The bottom line is therefore this: one is never able to prove or rule out a scientific theory beyond any doubt with experiments alone. That means that there will certainly be alternatives and it is unclear how theoretical virtues may help in theory selection. Having said that, I believe that scientific theories are powerful tools that can tell us about the nature of reality. Even if we cannot definitively prove they are true or false, they are either one or the other. There is something about the scientific method that allows science, as opposed to the unscientific alternatives like crystal ball gazing or tarot reading, to track truth, even if we do not know exactly what it is. Not knowing it yet does not imply we will never find out more. And not knowing what it is it does not mean that it does not work: my mum’s ignorance about the way in which a nuclear power plant works does not make the plant stop working.
So does anti-gravity exist? Either it does or it does not. We do not know yet and we will never be able to know for sure. However, science can still give fallible knowledge of the world: we sometime get things wrong but we are getting somewhere. Therefore, if you want to investigate the mysteries of gravity, as well as any other, keep studying, become a scientist and keep your philosophical eye open: the path is going to be uphill, but there is no fun without a challenge.
But it’s not a force. That was Einstein’s great discovery. How can we say that? Well because you can, at least for a while, simply make it vanish! How do you do that? Just let go! In other words, jump off a building, and you’ll feel no gravity as you fall down (hitting the Earth does not count as falling down). More gently, join a freely orbiting space station crew, and you’ll find life difficult because there will be no felt gravity to hold you down on your seat or to hold your coffee in a cup. In short, what appears to be a gravitational force actually depends, locally at least, on how you are moving. You can make it go away by allowing yourself to fall freely.
The reason this is true is because the gravitational mass of a body is the same as its inertial mass. This is what Galileo discovered, allegedly, by dropping objects of different weight from the Leaning Tower of Pisa (that experiment has since been done much more accurately by modern physicists - see this video for a feather and a ball falling at the same speed). That means that if you are in lift and the rope breaks, you and everything around you will fall at the same rate as the lift – so you will no longer feel gravity holding you to the floor of the lift. This was Einstein’s “happiest discovery”.
Gravity is now understood as being an effect of space-time curvature; in a static situation, of spatial curvature. A model is as follows: if you consider two aircraft that start off 1000 miles apart at the same instant from the Earth’s equator and they each fly at the same speed in an unchanging Northerly direction, they will get closer and closer together and will eventually collide at the North Pole. It is as if a force was pulling them together even though there was no attractive force acting between them. It was the curvature of the Earth that was the cause of this apparent force. Spacetime curvature is like that: if, for example, you let a spacecraft fall freely around the Earth at the right speed, with the engine turned off, it will arrive back exactly where it started because of the curvature of space caused by the Earth’s gravitational field. It never fired an engine to change direction but just kept going.
To really get to grips with this, you need to study tensor calculus. This is what Einstein had to learn when he was developing his theory of gravitation between 1912 and 1916 – he learnt it from a friend, and found it did exactly what was needed. The key idea is a curvature tensor: a mathematical object with 20 components (assuming spacetime is 4-dimensional, as all the evidence suggests). This resulted in the Einstein Field Equations, whereby 10 of these components (comprising the Ricci tensor) are determined at each point by the matter and energy present there, and another 10 components (comprising the Weyl tensor) are instead determined by the cumulative effects of all the matter and energy at other spacetime locations. It is the non-local effects of the Weyl tensor that convey curvature from one place to another, so letting us feel that gravitational tidal force due to the Moon on the Earth, and allowing the ripples in space-time that are gravitational waves to travel from distant colliding neutron stars and black holes to the Earth.
Einstein’s theory is a classical theory, and does not take quantum effects into account. Now most physicists assume that, at base, gravity, like all the other fields we know, is actually a quantum field. But despite stupendous efforts by a great many very talented physicists, we still don’t have a solid agreed-on theory of quantum gravity. So we don’t know the theory of gravity that would apply at the very start of the universe, or at the very end of the life of a Black Hole.
General Relativity has passed all these tests with flying colours. But some scientists, for example, are claiming you don’t need to have the huge amounts of dark matter in the universe that are suggested by standard studies – because they assume that General Relativity is correct. Maybe a modified gravitational theory, for example one in which the gravitational constant changes with space or time, might remove the need for dark matter. So many alternatives are being proposed and tested.
It is difficult to test on Earth because it is a long range force, It is dominant in the Universe on large scales because all gravitational mass is positive, unlike electricity, where there are equal numbers of positive and negatively charged particles.
We understand Einstein’s theory pretty well, despite its complexity. But that is not the end of the story. If you want to take part in the search for the ultimate answer, you will have to learn the maths (tensor calculus, maybe spinors) and the physics (variational principles and symmetry groups, for example) and then get going. No one knows what direction may lead to new and unexpected answers.
The universe is expanding, and Einstein’s theory of gravity makes a definite prediction about how the expansion rate should change over time: it should decrease, since the gravitational attraction between all the matter in the universe continually opposes the expansion.
The first time this prediction was observationally tested, around 1998, it was found to be spectacularly in error. The expansion of the universe is accelerating, not decelerating, and the acceleration has been going on for about six billion years.
How did cosmologists respond to this anomaly? If they adhered to the ideas of philosopher Karl Popper, they would have said: “Our theory of gravity has been conclusively disproved by the observations; therefore we will throw our theory out and start afresh.” In fact, they did something very different: they postulated the existence of a new, universe-filling substance which they called “dark energy”, and endowed dark energy with whatever properties were needed to reconcile the conflicting data with Einstein’s theory.
Philosophers of science are very familiar with this sort of thing (as was Popper himself). Dark energy is an example of what philosophers call an “auxiliary hypothesis”: something that is added to a theory in order to reconcile it with falsifying data. “Dark matter” is also an auxiliary hypothesis, invoked in order to explain the puzzling behavior of galaxy rotation curves.
Karl Popper first began thinking about these things around 1920, a time when intellectuals had many exciting new theories to think about: Einstein’s theory of relativity, Freud’s theory of psychoanalysis, Marx’s theory of historical materialism, etc. Popper noticed that Einstein’s theory differed from the theories of Freud and Marx in one important way. Freud and Marx (and their followers) appeared unwilling to acknowledge any counter-examples to their predictions; every observed fact was interpreted as confirmation of the theory. Whereas Einstein made definite predictions and was prepared to abandon his theory if the predictions were found to be incorrect.
Popper argued, in fact, that this difference is the essential difference between science and non-science. A scientist, Popper said, is someone who states—before a theory is tested—what observational or experimental results would falsify it. Popper’s “criterion of demarcation” is still the best benchmark we have for distinguishing science from non-science.
At the same time, Popper recognized an obvious logical flaw in his criterion. Theories, after all, are arbitrary; they are created out of thin air. What is to keep a scientist, Popper asked, from responding to an anomaly by saying: “Oh, wait, that is not the theory that I meant to test. What I actually meant to propose was a theory that contains this additional hypothesis”—a hypothesis that explains the anomalous new data. (This is precisely what some cosmologists do when they say that dark energy has been in Einstein’s theory all along.) Logically, this is perfectly kosher; but if scientists are allowed to proceed in this way - Popper realized - there could be no hope of ever separating science from non-science.
So Popper came up with a set of criteria for deciding when changes or additions to a theory were acceptable. The two most important were: (i) the modified theory must contain more content than the theory it replaces: that is, it must make some new, testable predictions; and (ii) at least some of the new predictions should be verified: the more unlikely a prediction in the light of the original theory, the stronger the corroboration of the modified theory when the prediction is shown to be correct. Popper did not simply propose these criteria; he argued for them on logical and probabilistic grounds. Popper was adamant that the total number of verified predictions was irrelevant in terms of judging the success of a theory since theories can always be adjusted to “explain” new data. All that matters, he said, are the novel predictions—predictions that no one had thought to make before the new theory came along.
How does the standard cosmological model—which contains Einstein’s theory of gravity as part of its “hard core”—fare according to the standards set by Popper? Here I can’t resist first quoting from Imre Lakatos, a student of Popper who tested and refined Popper’s criteria by comparing them with the historical record. Lakatos distinguished between what he called “progressive” and “degenerating” research programs:
"A research programme is said to be progressing as long as its theoretical growth anticipates its empirical growth, that is, as long as it keeps predicting novel facts with some success (`progressive problemshift’); it is stagnating if its theoretical growth lags behind its empirical growth, that is, as long as it gives only post-hoc explanations either of chance discoveries or of facts anticipated by, and discovered in, a rival programme (`degenerating problemshift’)."
(Lakatos invented the term ‘problemshift’ because, he said, “‘theoryshift’ sounds dreadful”.)
The standard cosmological model clearly fails to satisfy the criteria set by Lakatos for a progressive research program. Dark matter, dark energy, inflation all were added to the theory in response to unanticipated facts. None of these auxiliary hypotheses have yet been confirmed; for instance, attempts to detect dark matter particles in the laboratory have repeatedly failed. And the standard cosmological model is notoriously lacking in successful predictions; it seems always to be playing catch-up. The ability of the model to reproduce the spectrum of temperature fluctuations in the cosmic microwave background is often put forward as a notable success, but as astrophysicist Stacy McGaugh has pointed out, this success is achieved by varying the dozen or so parameters that define the model and some of those parameters are forced to have values that are stubbornly inconsistent with the values determined in other, more direct ways. This does not quite meet the standards for a successful novel prediction.
All of this would be of fairly academic interest, if not for one thing. It turns out that there exists an alternate theory (or “research program”) of gravity, which has been around since the early 1980’s, and which has quietly been racking up successful, novel predictions. As of this writing, about a dozen of its predictions—some quite startling when they were first made—have been verified observationally. And I am not aware of a single prediction from this research program that has been conclusively falsified.
I am referring here to the Milgromian research program. In 1983, Mordehai Milgrom suggested that galaxy rotation curves are flat—not because of dark matter—but because the laws of gravity and motion differ from those of Newton or Einstein in the regime of very low acceleration. Milgrom’s theory was designed to give flat rotation curves, and so the fact that it does so is not, of course, a novel prediction. But a long list of other predictions follow immediately from this single postulate. Milgrom outlined many of these predictions in his first papers from 1983 and a number of others have been pointed out since. One example: Milgrom’s postulate implies a unique, universal relation between the orbital speed in the outer parts of a galaxy, and the total mass (real, not dark) of the galaxy. No one had even thought to look for such a relation before Milgrom predicted it; no doubt because—according to the standard model—it is the dark matter, not the ordinary matter, that sets the rotation velocity. But Milgrom’s prediction has been splendidly confirmed—a beautiful example of a corroborated, novel prediction.
Milgrom’s theory is successful in another way that the standard model is not. In the early days of quantum theory, Max Planck pointed out that the convergence of various, independent determinations of Planck’s constant on 6.6 x 10-27 erg-sec was compelling evidence for a theory of quantized energy (exactly which theory of quantized energy was not yet clear). It would be almost miraculous, Planck argued, for such convergence to exist otherwise. In the same way, Milgrom has pointed out that the “acceleration constant” a0 that appears in his theory, and that marks the transition from Newtonian to non-Newtonian behavior, can be extracted from astrophysical data in many independent ways, all converging on the value ~ 1.2 x 10-10 m sec-2. As I noted above, nothing like this degree of convergence exists for the parameters that define the standard cosmological model.
What does all this mean? As a non-cosmologist, I have no stake in the correctness of any particular theory of cosmology or gravity. But I am impressed by the arguments of philosophers like Popper and Lakatos, and by the demonstrated power of their criteria to distinguish between successful theories and theories that end up on the rubbish heap. And so I am encouraged by the fact that there is a small, but growing, group of scientists who have chosen to develop Milgrom’s ideas. It is hard for me to believe that these scientists aren’t on the track of something important—quite possibly a new, and better, description of gravity.
DARK MATTER & BEYOND.
In deep underground laboratories, buried below rock and shielded from cosmic radiation, physicists have built extremely sensitive detectors aimed at solving one of the Universe’s greatest mysteries. They are awaiting signals of a new kind of particle, promised to them by cosmologists and astrophysicists: Dark Matter. The highly elusive particle is thought to dominate the mass budget of our galaxy and of the Universe as such. There should be about six times more Dark Matter than ordinary, “baryonic” matter (which includes everything from interstellar gas clouds, stars, and planets, to the screen you are reading this on, and you yourself). Dark Matter has not yet been directly detected, despite numerous experiments, their painstaking efforts to reduce background signals, and thus ever increasing sensitivity. Many researchers nevertheless remain confident that a detection is within reach. Yet some worry: what if we are chasing a phantom? What if Dark Matter does not exist?
There are several lines of argument for the existence of Dark Matter. On the scale of galaxies, the need for Dark Matter is mostly inferred from their dynamics. Disk galaxies rotate. Counting up the distribution of mass visible in a galaxy – in the form of stars and gas – we can use Newton’s law of gravity to calculate how fast the galaxy should rotate at different distances from its center (the “rotation curve”). The rotation should be faster in the center and slower with increasing distance. Yet measurements reveal that galaxies rotate faster than expected and that the rotation velocity does not drop at increasing radii. Taken at face value, this would imply that galaxies are not gravitationally bound; the gravity of their stars and gas is insufficient to keep them from flying apart. To be stable, galaxies would have to contain large amounts of unseen mass. This mass has been termed “Dark” Matter because it only interacts through gravity, but not with electromagnetic radiation.
This argument for Dark Matter implies one crucial assumption: Newton’s law of gravity applies on galactic scales. This is a long stretch. Newton’s law was uncovered on Earth, where the gravitational acceleration is 1011 times stronger than typical for galaxies, and in the Solar system, where even the most distant planet Neptune experiences a 10,000 times stronger acceleration than stars in galaxies. It is therefore far from confirmed whether Newton’s law can be extrapolated to the very low acceleration regime that galaxies live in.
This was also noticed by Israeli physicist Mordehai Milgrom. In 1983, he suggested a radically different approach to explain the high rotation speeds of galaxies. Instead of introducing Dark Matter, Milgrom proposed that the laws of gravity are different on the scale of galaxies – that Newtonian Dynamics becomes “Modified Newtonian Dynamics” (MOND). In MOND, or Milgromian Dynamics, the gravitational acceleration of a given mass is stronger than in the Newtonian case, and does not scale as 1/r2 with distance r but rather as 1/r. This explains why galaxies rotate fast without tearing themselves apart, and why the rotation curve does not drop at larger radii. Since MOND must preserve the successes of Newtonian gravity, which is very well tested in the solar system, there has to be an acceleration at which a transition occurs. This acceleration scale is called a0.
The parameter a0 is not fixed by the theory. It has to be measured. Such measurements provide a first test. Does every galaxy require the same a0, or does the parameter have to be fixed for each system independently? The former is consistent with a fundamental theory, whereas the latter would be much less convincing. It turns out that the former is indeed the case: every galaxy results in the same a0. In fact, the parameter can be measured in several independent ways, not only for different galaxies. They all point to the same value.
One hallmark of a scientific hypothesis is that it makes testable predictions. Dark Matter cosmology makes predictions for the large-scale evolution of the universe and for statistical samples of galaxies. However, it has almost no predictive power for an individual galaxy. While the rotation curve of a galaxy can be fitted by adding a distribution of Dark Matter to it, this does not work the other way around. Given just the distribution of stars and gas in a galaxy, Dark Matter models do not predict the detailed rotation curve. The visible galaxy could, in principle, be embedded in a variety of different Dark Matter distributions, all resulting in different rotation curves.
MOND, in contrast, makes precise and accurate predictions for individual galaxies. If the distribution of stars and gas in a galaxy is known, Milgrom’s law allows us to calculate what its rotation curve should look like, down to bumps and wiggles. These predictions are routinely confirmed observationally.
While a modified gravity law offers a conceptual explanation for why such predictions work, the underlying, extremely tight correlation is purely empirical and independent of MOND. It has been termed the Radial Acceleration Relation (RAR). One cannot stress enough how fascinating it is that the distribution of baryons (stars, gas) in a galaxy uniquely predicts the galaxy’s dynamics. This observational fact must be understood in any model of the Universe, especially in Dark Matter models in which such predictability is not necessarily expected.
Nevertheless, MOND does have problems if applied beyond the regime of galaxies for which it was developed. An example is galaxy clusters, large agglomerations of galaxies that even in MOND appear to require the addition of Dark Matter to be bound structures (albeit of only a factor of about two compared to the ordinary matter). A related issue is colliding galaxy clusters such as the Bullet Cluster, in which the mass distribution inferred from gravitational lensing also appears more consistent with the presence of Dark Matter than with a modified gravity interpretation. However, what is often neglected in discussing this issue is that the clusters’ collision speed is surprisingly high for Dark Matter cosmology, but more reasonable in MOND. The Bullet Cluster thus neither uniquely supports nor uniquely falsifies either of the two competing concepts.
In a sense, Dark Matter and MOND have distinct regimes of applicability. The former is more successful on larger scales, while the latter is most successful on smaller scales, being able to predict galaxy dynamics and also offering an explanation for several observed scaling relations between galaxy properties. Once we attempt to expand the models beyond their respective regimes of primary applicability, problems appear. Dark Matter models suffer from a number of “small-scale problems” on the scale of galaxies and their satellite galaxy populations. MOND cannot be successfully applied to large systems of galaxies or the universe as a whole.
This apparent complementarity could offer a way out of the current conceptual stalemate. Some physicists are developing models that join the two seemingly incompatible approaches. One example is Superfluid Dark Matter, developed by Justin Khoury at UPenn. In this model, Dark Matter around galaxies phase-transitions into a superfluid, which gives rise to a MOND-like behavior for ordinary matter, but only in this region. Interestingly, this results in some predictions that are distinct from those of both “pure” Dark Matter and MOND, making this a testable alternative born out of two competing concepts.
Laboratory searches for Dark Matter are important. They hold the potential for a groundbreaking detection confirming the hypothesis. However, detectability is not falsifiability. What if we do not succeed in detecting Dark Matter? The reason could be that Dark Matter really does not interact with ordinary matter except gravitationally, or because it does not exist. One can imagine falling for a sunk-cost fallacy in such a case, by sticking with the Dark Matter hypothesis because of the amount of resources already invested in it. To prevent such a risk, we should already be considering and developing alternative approaches. Maybe the best argument for this is the predictive power of MOND. Since this is an empirical success linking the observed distribution of stars and gas directly to their velocities, it will have to be understood in any successful model of cosmology, including those based on Dark Matter. Therefore research into models based on the modified gravity concept are a worthwhile addition to the Dark Matter approach. A diversity of ideas (as well as people) should be cherished and supported. Ultimately, building on the successes of both the Dark Matter and the modified gravity approach might offer the crucial insights necessary to unravel the composition of the universe and the nature of gravity.
How our universe has begun?
On the center of our galaxy where was born the sun by very light proto particles the very first orbital system representing “hydrogen atom” by two almost equal proto particles the force is very small almost inclining to zero (if you like can call it proto electrical force). Afterwards the “light ray” (proto field) reaches another and another masses which increases inertia of the very first “hydrogen orbital system” and the nucleus (proto proton) is shrinking because the distance to proto electron is increases. Because the proto electron is on the periphery it is shrinking slowly than the nucleus (proton). That is expansion of the universe from our position of observation – proto hydrogen and begin to differentiates the electrostatic and gravitational forces and appears the phenomenon energy itself all because of the expansion of the universe, see part II USM www.kanevuniverse.com
What is the essence of the energy in the universe itself and from where it comes from and what is its value? From page 96, 97, 98 USM www.kanevuniverse.com follows that in the beginning of springing up of Our space the full energy is equal to zero for us. Then with thickening of the micro cosmos and expanding of macro cosmos due to the asymmetry of these coefficients, which depends by our position of observation in this case our living position, we have the illusion that the energy for us is increases, because we are close to the nuclei of the atoms rather than the stars and galaxy. But the macro cosmos expands more rapidly by the same reason, so full energy in our space is again equal to zero. So it is seen that the energy is “one reality in the illusion”, as well as the world itself! See USM www.kanevuniverse.com So by this very elegant way (haw has liking to said Einstein himself) is determinates one of the most mysterious physical phenomenon in the universe!
About forces do surrounding us in our world. That is right Brian with one very important correction. In fact these three forces electrostatic gravitational and nuclear are the same force, but only the thickening of the space around us, during the expansion of the universe (actually only our galaxy) gradually forms their quantity differences and deludes us that they are three different forces. That is explained in detail on part II USM www.kanevuniverse.com Quality identity and inertial character of these three forces is explained in part I on the same site. The rest namely the polarization of the space and following there essence of the weak and strong interaction is shown here: On pages 55, 56, 57 USM www.kanevuniverse.com is shown the essence of polarization of the space and the equation of that, which is universally about the all stable fields: gravitational, electromagnetic and nuclear and explain in very simple and convincing way behavior of strong and weak interactions. In particular it is explains the belts of Jupiter and Saturn and their approximately sizes. Most important conclusion is that these belts have relativistic velocity of birth, which leads to the conclusion that these two planets are the most dangerous place on the solar system.
Another case of delusion that physicist made up about originate of the universe. The premature conclusion is based upon the data of neutrino registration deep underground (under ice) in Antarctica, where for about several years was registered some ten of cases: several high energy neutrinos and some ten cases relatively low energy neutrinos….. that are the facts! There is necessary a lot much years of confirming such cases to be sure from what directions come mainly these particles and to estimate the energy spectrum through more cases observing. So the experiment is far away from the conclusions. But some physicist instantly decided that this is evidence about “big bang” “young stars” and soon. And all these, if the physics nowadays can’t say anything about the essence of these mysterious particles called neutrino! Let me explain: According to USM www.kanevuniverse.com in the beginning when our space (universe) was started in the center of our galaxy, that started is with very first orbital system containing only two proto particles representing very first “hydrogen atom” from two almost equal proto particles with mass 1,8.10 rising to a 13 power times smaller than the mass of proton. In this moment with appearance of this very first orbital system appears the energy itself as well and this energy is almost equal to zero and the first real value appears together with the first difference between the masses of the two proto particles. And that difference appears because of the beginning of space expansion provoked by the added new masses (proto particles), which disturb the inertial balance of this very first orbital system (see part I USM). That was our universe in this very first moment. Then begin to expands the macro cosmos and begin respectively to thickening the micro cosmos, which means that the nuclear proto particle in the beginning orbital system begin to weigh more quickly than the orbiting proto particle, because the first is on the center (more close to the micro cosmos). How it is seen the two particles during movement towards the periphery of our galaxy come to our position of observation where the central particle already has the mass of proton and the orbiting one possesses mass of electron, so in our position of observation the proton has resonance radius equal to the size of proton (see USM) and the electron has resonance radius equal to the size of atom. But what has happened with expansion of the macro cosmos (our galaxy) looked at our position of observation? The resonance radius of the first proto particle in the very first orbital system (“hydrogen atom”) in fact is the size of this very first orbital system, so during the expansion of the macro cosmos this resonance radius begin to expands which means that it represents more and more lightering of the proto particle mass and when this process come to our point of observation this particle already has the mass of neutrino, see page 128 to 138 USM www.kanevuniverse.com In the formulae 125 and 126 is given the masses spectrum of electronic neutrino and the masses spectrum of muon neutrino and the explanation for that. So the high energy spectrum neutrinos actually comes from the smaller resonance radius in any galaxy (more closer belts of centripetal accelerations) and lower spectrum respectively comes from the periphery belts of centripetal accelerations again in any galaxy. So obviously observed here neutrinos has nothing to do with “big bang” and so for absurdity!
Post a Comment
let noble thoughts come to us from all around