Quantum Gravity is actually a very viable alternative, and there are also numerous alternatives to the existence of dark matter, dark energy, etc, like Modified Newtonian Dynamics. The existence of multiple dimensions and alternative universes, while mathematically eloquent, has yet to be proven, but with high energy physics probing farther and farther, I think that its just a matter of time. Gravity, the weakest of the four fundamental forces is hypothesized to originate outside of normal space-time, which makes sense if you consider that singularities like black holes are the strongest source of gravity– perhaps because they have pinched themselves out of space-time and are closest to the ultimate “source” of gravity. I do believe that gravity is as out of place among the four known forces as time is among the four known dimensions– and the two are inextricably connected. Read this interesting article of Closed TimeLike Curves, which are a property of relativity and occur near black holes.

http://en.wikipedia….timelike_curves

In a Lorentzian manifold, a closed timelike curve (CTC) is a worldline of a material particle in spacetime that is “closed,” returning to its starting point. This possibility was first raised by Kurt Gödel in 1949, who discovered a solution to the equations of general relativity (GR) allowing CTCs known as the Gödel metric, and since then other GR solutions containing CTCs have been found, such as the Tipler cylinder and traversable wormholes. If CTCs exist, their existence would seem to imply at least the theoretical possibility of time travel backwards in time, raising the spectre of the grandfather paradox. Some physicists speculate that the CTCs which appear in certain GR solutions might be ruled out by a future theory of quantum gravity which would replace GR, an idea which Stephen Hawking has labeled the chronology protection conjectur

One feature of a CTC is that it opens the possibility of a worldline which is not connected to earlier times, and so the existence of events that cannot be traced to an earlier cause. Ordinarily, causality demands that each event in spacetime is preceded by its cause in every rest frame. This principle is critical in determinism, which in the language of general relativity states complete knowledge of the universe on a spacelike Cauchy surface can be used to calculate the complete state of the rest of spacetime. However, in a CTC, causality breaks down, because an event can be “simultaneous” with its cause – in some sense an event may be able to cause itself. It is impossible to determine based only on knowledge of the past whether or not something exists in the CTC that can interfere with other objects in spacetime. A CTC therefore results in a Cauchy horizon, and a region of spacetime that cannot be predicted from perfect knowledge of some past time.

http://en.wikipedia….tonian_dynamics

In physics, Modified Newtonian dynamics (MOND) is a hypothesis that proposes a modification of Newton’s law of gravity to explain the galaxy rotation problem. When the uniform velocity of rotation of galaxies was first observed, it was unexpected because Newtonian theory of gravity predicts that objects that are farther out will have lower velocities. For example, planets in the Solar System orbit with velocities that decrease as their distance from the Sun increases.

MOND was proposed by Mordehai Milgrom in 1983 as a way to model this observed uniform velocity data. [1] Milgrom noted that Newton’s law for gravitational force has been verified only where gravitational acceleration is large, and suggested that for extremely low accelerations the theory may not hold. MOND theory posits that acceleration is not linearly proportional to force at low values.

MOND stands in contrast to the more widely accepted theory of dark matter. Dark matter theory suggests that each galaxy contains a halo of an as yet unidentified type of matter that provides an overall mass distribution different from the observed distribution of normal matter. This dark matter modifies gravity so as to cause the uniform rotation velocity data.

According to the Modified Newtonian Dynamics theory, every physical process that involves small accelerations due to gravity will have an outcome different from that predicted by the simple law F=ma. Therefore, astronomers need to look for all such processes and verify that MOND remains compatible with observations, that is, within the limit of the uncertainties on the data. There is, however, a complication overlooked up to this point but that strongly affects the compatibility between MOND and the observed world: in a system considered as isolated, for example a single satellite orbiting a planet, the effect of MOND results in an increased velocity beyond a given range (actually, below a given acceleration, but for circular orbits it is the same thing) that depends on the mass of both the planet and the satellite. However, if the same system is actually orbiting a star, the planet and the satellite will be accelerated in the star’s gravitational field. For the satellite, the sum of the two fields could yield acceleration greater than a0, and the orbit would not be the same as that in an isolated system.

For this reason, the typical acceleration of any physical process is not the only parameter astronomers must consider. Also critical is the process’s environment, which is all external forces that are usually neglected. In his paper, Milgrom arranged the typical acceleration of various physical processes in a two-dimensional diagram. One parameter is the acceleration of the process itself, the other parameter is the acceleration induced by the environment.

This affects MOND’s application to experimental observation and empirical data because all experiments done on Earth or its neighborhood are subject to the Sun’s gravitational field, and this field is so strong that all objects in the Solar system undergo an acceleration greater than a0. This explains why the flattening of galaxies’ rotation curve, or the MOND effect, had not been detected until the early 1980s, when astronomers first gathered empirical data on the rotation of galaxies.

Therefore, only galaxies and other large systems are expected to exhibit the dynamics that will allow astronomers to verify that MOND agrees with observation. Since Milgrom’s theory first appeared in 1983, the most accurate data has come from observations of distant galaxies and neighbors of the Milky Way. Within the uncertainties of the data, MOND has remained valid. The Milky Way itself is scattered with clouds of gas and interstellar dust, and until now it has not been possible to draw a rotation curve for the galaxy. Finally, the uncertainties on the velocity of galaxies within clusters and larger systems have been too large to conclude in favor of or against MOND. Indeed, conditions for conducting an experiment that could confirm or disprove MOND can only be performed outside the Solar system — farther even than the positions that the Pioneer and Voyager space probes have reached[citation needed].

In search of observations that would validate his theory, Milgrom noticed that a special class of objects, the low surface brightness galaxies (LSB), is of particular interest: the radius of an LSB is large compared to its mass, and thus almost all stars are within the flat part of the rotation curve. Also, other theories predict that the velocity at the edge depends on the average surface brightness in addition to the LSB mass. Finally, no data on the rotation curve of these galaxies was available at the time. Milgrom thus could make the prediction that LSBs would have a rotation curve which is essentially flat, and with a relation between the flat velocity and the mass of the LSB identical to that of brighter galaxies.

Since then, the majority of LSBs observed has been consistent with the rotational curve predicted by MOND.[4]

An exception to MOND other than LSB is prediction of the speeds of galaxies that gyrate around the center of a galaxy cluster. Our galaxy is part of the Virgo supercluster. MOND predicts a rate of rotation of these galaxies about their center, and temperature distributions, that are contrary to observation.[5][6]

One experiment that might test MOND would be to observe the particles proposed to contribute to the greater part of the Universe’s mass; several experiments are endeavoring to do this under the assumption that the particles have weak interactions.[citation needed] Another approach to test MOND is to apply it to the evolution of cosmic structure or to the dynamics and evolution of observed galaxies.[citation needed].

A recent proposal is that MOND successfully predicts the local galactic escape speed of the Milky Way, a measure of the mass beyond the galactocentric radius of the Sun.[7]

Lee Smolin and co-workers have tried unsuccessfully to obtain a theoretical basis for MOND from quantum gravity. His conclusion is “MOND is a tantalizing mystery, but not one that can be resolved now.”[8]

If you look at the “weird” behavior of quantum particles (like quantum teleportation) or how virtual particles can literally wink in and out of existence (the Casimir Effect), the most eloquent explanation does involve random fluctuations of quantum density via folding– something that if we can control on a larger level, can open a vast source of energy for us– which we can use to probe the universe (or universes) even further. I do agree with you that the closer we think we are to the “solution” the more we realize that there is no final solution.

One of the most fascinating ideas Ive heard Hawkings come up with, besides the idea of bubble universes, each with its own set of physical laws and constants, determining form and structure, is the idea of an extra dimension of time, or imaginary time. The idea of multiple dimensions of time makes time travel much more plausible in my mind (just like multiple higher spatial dimensions makes FTL achievable by folding space-time through higher dimensions (perhaps through transversable wormholes, which might actually be possible through a spinning black hole, its centrifugal force balancing out the intense gravity near the center, allowing safe “passage”– in other words, the same way the universe expanded during its Inflationary Period– an aspect of the Big Bang theory widely accepted now– which is where the idea of Dark Flow comes from– which are objects of mass existing beyond the number of light years the universe is known to exist, detectable by their gravitational pull on closer-in objects.). And if you can travel along more than one set of coordinates in the temporal plane then you should be able to have multiple temporal streams or branches and should be able to go to the past and future without violating causality and causing paradoxes.

http://en.wikipedia…./Imaginary_time

Imaginary time is difficult to visualize. If we imagine “regular time” as a horizontal line running between “past” in one direction and “future” in the other, then imaginary time would run perpendicular to this line as the imaginary numbers run perpendicular to the real numbers in the complex plane. However, imaginary time is not imaginary in the sense that it is unreal or made-up — it simply runs in a direction different from the type of time we experience. In essence, imaginary time is a way of looking at the time dimension as if it were a dimension of space: you can move forward and backward along imaginary time, just like you can move right and left in space.

The concept is useful in cosmology because it can help smooth out gravitational singularities in models of the universe (see Hartle-Hawking state). Singularities pose a problem for physicists because these are areas where known physical laws do not apply. The Big Bang, for example, appears as a singularity in “regular time.” But when visualized with imaginary time, the singularity is removed and the Big Bang functions like any other point in spacetime.

http://en.wikipedia….ationary_theory

In physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized exponential expansion of the universe at the end of the grand unification epoch, 10−36 seconds after the Big Bang, driven by a negative-pressure vacuum energy density.[1] The term “inflation” is also used to refer to the hypothesis that inflation occurred, to the theory of inflation, or to the inflationary epoch.

While the detailed particle physics mechanism responsible for inflation is not known, the basic picture makes a number of predictions that have been confirmed by observation. Inflation is thus now considered part of the standard hot big bang cosmology. The hypothetical particle or field thought to be responsible for inflation is called the inflaton.

http://en.wikipedia.org/wiki/Wormhole

Lorentzian traversable wormholes would allow travel from one part of the universe to another part of that same universe very quickly or would allow travel from one universe to another. The possibility of traversable wormholes in general relativity was first demonstrated by Kip Thorne and his graduate student Mike Morris in a 1988 paper; for this reason, the type of traversable wormhole they proposed, held open by a spherical shell of exotic matter, is referred to as a Morris-Thorne wormhole. Later, other types of traversable wormholes were discovered as allowable solutions to the equations of general relativity, including a variety analyzed in a 1989 paper by Matt Visser, in which a path through the wormhole can be made in which the traversing path does not pass through a region of exotic matter. However in the pure Gauss-Bonnet theory exotic matter is not needed in order for wormholes to exist- they can exist even with no matter.[2] A type held open by negative mass cosmic strings was put forth by Visser in collaboration with Cramer et al.,[3] in which it was proposed that such wormholes could have been naturally created in the early universe.

Wormholes connect two points in spacetime, which means that they would in principle allow travel in time, as well as in space. In 1988, Morris, Thorne and Yurtsever worked out explicitly how to convert a wormhole traversing space into one traversing time.[4] However, it has been said a time traversing wormhole cannot take a person back to before it was made[citation needed] but this is disputed

Faster-than-light travel

Special relativity only applies locally. Wormholes allow superluminal (faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole, the time taken to traverse it would be less than the time it would take a light beam to make the journey if it took a path through the space outside the wormhole. However, a light beam traveling through the wormhole would always beat the traveler. As an analogy, running around to the opposite side of a mountain at maximum speed may take longer than walking through a tunnel crossing it.
[edit]
Time travel

A wormhole could allow time travel.[4] This could be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around. This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry.

For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth’s clock reading 2005 while the stationary mouth’s clock read 2010. A traveller who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle’s world line to form a closed loop in spacetime, known as a closed timelike curve.

It is thought that it may not be possible to convert a wormhole into a time machine in this manner; some analyses using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it, in keeping with the chronology protection conjecture. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. The debate on this matter is described by Kip S. Thorne in the book Black Holes and Time Warps. There is also the Roman ring, which is a configuration of more than one wormhole. This ring seems to allow a closed time loop with stable wormholes when analyzed using semiclassical gravity, although without a full theory of quantum gravity it is uncertain whether the semiclassical approach is reliable in this case.

Characterizing inter-universe wormholes is more difficult. For example, one can imagine a ‘baby’ universe connected to its ‘parent’ by a narrow ‘umbilicus’. One might like to regard the umbilicus as the throat of a wormhole, but the spacetime is simply connected.

By the way, going back to the discussion about Gravity, Loop Quantum Gravity seems to have some legs…

http://en.wikipedia….um_loop_gravity

Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity. Loop quantum gravity suggests that space can be viewed as an extremely fine fabric or network “weaved” of finite quantised loops of excited gravitational fields called spin networks. When viewed over time, these spin networks are called spin foam, which should not be confused with quantum foam. A major grand unified theory contender with string theory, loop quantum gravity incorporates general relativity without requiring string theory’s higher dimensions.

LQG preserves many of the important features of general relativity, while simultaneously employing quantization of both space and time at the Planck scale in the tradition of quantum mechanics. The technique of loop quantization was developed for the nonperturbative quantization of diffeomorphism-invariant gauge theory. Roughly, LQG tries to establish a quantum theory of gravity in which the very space itself, where all other physical phenomena occur, becomes quantized.

LQG is one of a family of theories called canonical quantum gravity. The LQG theory also includes matter and forces, but does not address the problem of the unification of all physical forces the way some other quantum gravity theories such as string theory do.

Earlier, I talked about how the Casimir Effect might be linked to the idea of the existence of other dimensions and universes. Quite independently of the following article, my idea was that microwormholes exist within the fabric of space-time that allow these virtual particles to transport between different dimensions and/or universes… preserving the Law of Conservation of Mass-Energy, but on a higher scale (call it the Multiverse scale if you will.) In other words, virtual particles coming into and out of existence out of nowhere dont violate conservation laws because they were teleported into and out of space time, but from our perspective they seem to wink into and out of existence– literally from nowhere and to nowhere. Imagine my surprise when I found the following piece on wiki:

http://en.wikipedia….ki/Quantum_foam

Relation to other theories

Quantum foam is theorized to be created by virtual particles of very high energy. Virtual particles appear in quantum field theory, where they arise briefly and then annihilate during particle interactions, in such a way that they affect the measured outputs of the interaction even though the virtual particles are themselves never directly observed. They can also appear and annihilate briefly in empty space, and these “vacuum fluctuations” affect the properties of the vacuum, giving it a nonzero energy known as vacuum energy, a type of zero-point energy (however, physicists are uncertain about the magnitude of this energy [3]). The Casimir effect can also be understood in terms of the behavior of virtual particles in the empty space between two parallel plates. Ordinarily quantum field theory does not deal with virtual particles of sufficient energy to curve spacetime significantly, so quantum foam is a speculative extension of these concepts which imagines the consequences of such high-energy virtual particles at very short distances and times.

The “foamy” spacetime would look like a complex turbulent storm-tossed sea. Some physicists theorize the formation of wormholes therein; speculation arising from this includes the possibility of hyperspatial links to other universes.

Advertisements