Faster-than-light

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Faster-than-light

Because the sphere travels faster than light, the observer sees nothing until it has already passed. Then, two images appear: one of the sphere arriving (on the right) and one of it departing (on the left).

Faster-than-light (superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light in vacuum (c). The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster.

Particles whose speed exceeds that of light (tachyons) have been hypothesized, but their existence would violate causality and would imply time travel. The scientific consensus is that they do not exist.

According to all observations and current scientific theories, matter travels at slower-than-light (subluminal) speed with respect to the locally distorted spacetime region. Speculative faster-than-light concepts include the Alcubierre drive, Krasnikov tubes, traversable wormholes, and quantum tunneling. Some of these proposals find loopholes around general relativity, such as by expanding or contracting space to make the object appear to be travelling greater than c. Such proposals are still widely believed to be impossible as they still violate current understandings of causality, and they all require fanciful mechanisms to work (such as requiring exotic matter).

Superluminal travel of non-information

Main article: Superluminal motion

In the context of this article, "faster-than-light" means the transmission of information or matter faster than c, a constant equal to the speed of light in vacuum, which is 299,792,458 m/s (by definition of the metre) or about 186,282.397 miles per second. This is not quite the same as traveling faster than light, since:

• Some processes propagate faster than c, but cannot carry information (see examples in the sections immediately following).
• In some materials where light travels at speed c/n (where n is the refractive index) other particles can travel faster than c/n (but still slower than c), leading to Cherenkov radiation (see phase velocity below).

Neither of these phenomena violates special relativity or creates problems with causality, and thus neither qualifies as faster-than-light as described here.

In the following examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity.

Daily sky motion

For an earth-bound observer, objects in the sky complete one revolution around the Earth in one day. Proxima Centauri, the nearest star outside the Solar System, is about four and a half light-years away. In this frame of reference, in which Proxima Centauri is perceived to be moving in a circular trajectory with a radius of four light years, it could be described as having a speed many times greater than c as the rim speed of an object moving in a circle is a product of the radius and angular speed. It is also possible on a geostatic view, for objects such as comets to vary their speed from subluminal to superluminal and vice versa, simply because the distance from the Earth varies. Comets may have orbits which take them out to more than 1000 AU. The circumference of a circle with a radius of 1000 AU is greater than one light day. In other words, a comet at such a distance is superluminal in a geostatic, and therefore non-inertial, frame of reference.

Light spots and shadows

If a laser beam is swept across a distant object, the spot of laser light can seem to move across the object at a speed greater than c. Similarly, a shadow projected onto a distant object seems to move across the object faster than c. In neither case does the light travel from the source to the object faster than c, nor does any information travel faster than light. No object is moving in these examples. For comparison, consider water squirting out of a garden hose as it is swung side to side: water does not instantly follow the direction of the hose.

Closing speeds

The rate at which two objects in motion in a single frame of reference get closer together is called the mutual or closing speed. This may approach twice the speed of light, as in the case of two particles travelling at close to the speed of light in opposite directions with respect to the reference frame.

Imagine two fast-moving particles approaching each other from opposite sides of a particle accelerator of the collider type. The closing speed would be the rate at which the distance between the two particles is decreasing. From the point of view of an observer standing at rest relative to the accelerator, this rate will be slightly less than twice the speed of light.

Special relativity does not prohibit this. Instead, it implies that it is wrong to use Galilean relativity to compute the velocity of one of the particles, as would be measured by an observer traveling alongside the other particle. That is, special relativity gives the correct velocity-addition formula for computing such relative velocity.

It is instructive to compute the relative velocity of particles moving at v and −v in accelerator frame, which corresponds to the closing speed of 2v > c. Expressing the speeds in units of c, β = v/c:

${\displaystyle {\beta }_{\text{rel}}=\frac{\beta +\beta }{1+{\beta }^2}=\frac{2\beta }{1+{\beta }^2}\le 1.}$

Proper speeds

If a spaceship travels to a planet one light-year (as measured in the Earth's rest frame) away from Earth at high speed, the time taken to reach that planet could be less than one year as measured by the traveller's clock (although it will always be more than one year as measured by a clock on Earth). The value obtained by dividing the distance traveled, as determined in the Earth's frame, by the time taken, measured by the traveller's clock, is known as a proper speed or a proper velocity. There is no limit on the value of a proper speed as a proper speed does not represent a speed measured in a single inertial frame. A light signal that left the Earth at the same time as the traveller would always get to the destination before the traveller would.

Phase velocities above c

The phase velocity of an electromagnetic wave, when traveling through a medium, can routinely exceed c, the vacuum velocity of light. For example, this occurs in most glasses at X-ray frequencies. However, the phase velocity of a wave corresponds to the propagation speed of a theoretical single-frequency (purely monochromatic) component of the wave at that frequency. Such a wave component must be infinite in extent and of constant amplitude (otherwise it is not truly monochromatic), and so cannot convey any information. Thus a phase velocity above c does not imply the propagation of signals with a velocity above c.

Group velocities above c

The group velocity of a wave may also exceed c in some circumstances. In such cases, which typically at the same time involve rapid attenuation of the intensity, the maximum of the envelope of a pulse may travel with a velocity above c. However, even this situation does not imply the propagation of signals with a velocity above c, even though one may be tempted to associate pulse maxima with signals. The latter association has been shown to be misleading, because the information on the arrival of a pulse can be obtained before the pulse maximum arrives. For example, if some mechanism allows the full transmission of the leading part of a pulse while strongly attenuating the pulse maximum and everything behind (distortion), the pulse maximum is effectively shifted forward in time, while the information on the pulse does not come faster than c without this effect. However, group velocity can exceed c in some parts of a Gaussian beam in vacuum (without attenuation). The diffraction causes the peak of the pulse to propagate faster, while overall power does not.

Cosmic expansion

According to Hubble's law, the expansion of the universe causes distant galaxies to appear to recede from the Earth faster than the speed of light. However, the recession speed associated with Hubble's law, defined as the rate of increase in proper distance per interval of cosmological time, is not a velocity in a relativistic sense. Moreover, in general relativity, velocity is a local notion, and there is not even a unique definition for the relative velocity of a cosmologically distant object. Faster-than-light cosmological recession speeds are entirely a coordinate effect.

There are many galaxies visible in telescopes with redshift numbers of 1.4 or higher. All of these have cosmological recession speeds greater than the speed of light. Because the Hubble parameter is decreasing with time, there can actually be cases where a galaxy that is receding from the Earth faster than light does manage to emit a signal which reaches the Earth eventually.

However, because the expansion of the universe is accelerating, it is projected that most galaxies will eventually cross a type of cosmological event horizon where any light they emit past that point will never be able to reach the Earth any time in the infinite future, because the light never reaches a point where its "peculiar velocity" towards the Earth exceeds the expansion velocity away from the Earth (these two notions of velocity are also discussed in Comoving and proper distances § Uses of the proper distance). The current distance to this cosmological event horizon is about 16 billion light-years, meaning that a signal from an event happening at present would eventually be able to reach the Earth in the future if the event was less than 16 billion light-years away, but the signal would never arrive if the event was more than 16 billion light-years away.

Astronomical observations

Apparent superluminal motion is observed in many radio galaxies, blazars, quasars, and recently also in microquasars. The effect was predicted before it was observed by Martin Rees and can be explained as an optical illusion caused by the object partly moving in the direction of the observer, when the speed calculations assume it does not. The phenomenon does not contradict the theory of special relativity. Corrected calculations show these objects have velocities close to the speed of light (relative to our reference frame). They are the first examples of large amounts of mass moving at close to the speed of light. Earth-bound laboratories have only been able to accelerate small numbers of elementary particles to such speeds.

Quantum mechanics

Certain phenomena in quantum mechanics, such as quantum entanglement, might give the superficial impression of allowing communication of information faster than light. According to the no-communication theorem these phenomena do not allow true communication; they only let two observers in different locations see the same system simultaneously, without any way of controlling what either sees. Wavefunction collapse can be viewed as an epiphenomenon of quantum decoherence, which in turn is nothing more than an effect of the underlying local time evolution of the wavefunction of a system and all of its environment. Since the underlying behavior does not violate local causality or allow faster-than-light communication, it follows that neither does the additional effect of wavefunction collapse, whether real or apparent.

The uncertainty principle implies that individual photons may travel for short distances at speeds somewhat faster (or slower) than c, even in vacuum; this possibility must be taken into account when enumerating Feynman diagrams for a particle interaction. However, it was shown in 2011 that a single photon may not travel faster than c.

There have been various reports in the popular press of experiments on faster-than-light transmission in optics — most often in the context of a kind of quantum tunnelling phenomenon. Usually, such reports deal with a phase velocity or group velocity faster than the vacuum velocity of light. However, as stated above, a superluminal phase velocity cannot be used for faster-than-light transmission of information.

Hartman effect

Main article: Hartman effect

The Hartman effect is the tunneling effect through a barrier where the tunneling time tends to a constant for large barriers. This could, for instance, be the gap between two prisms. When the prisms are in contact, the light passes straight through, but when there is a gap, the light is refracted. There is a non-zero probability that the photon will tunnel across the gap rather than follow the refracted path.

However, it has been claimed that the Hartman effect cannot actually be used to violate relativity by transmitting signals faster than c, also because the tunnelling time "should not be linked to a velocity since evanescent waves do not propagate". The evanescent waves in the Hartman effect are due to virtual particles and a non-propagating static field, as mentioned in the sections above for gravity and electromagnetism.

Casimir effect

Main article: Casimir effect

In physics, the Casimir–Polder force is a physical force exerted between separate objects due to resonance of vacuum energy in the intervening space between the objects. This is sometimes described in terms of virtual particles interacting with the objects, owing to the mathematical form of one possible way of calculating the strength of the effect. Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. Because the effect is due to virtual particles mediating a static field effect, it is subject to the comments about static fields discussed above.

EPR paradox

Main article: EPR paradox

The EPR paradox is a thought experiment of Albert Einstein, Boris Podolsky and Nathan Rosen, and is named after their surnames. In this experiment, the two measurements of an entangled state are correlated even when the measurements are distant from the source and each other. However, no information can be transmitted this way; the answer to whether or not the measurement actually affects the other quantum system comes down to which interpretation of quantum mechanics one subscribes to.

An experiment performed in 1997 by Nicolas Gisin has demonstrated quantum correlations between particles separated by over 10 kilometers. But as noted earlier, the non-local correlations seen in entanglement cannot actually be used to transmit classical information faster than light, so that relativistic causality is preserved. The situation is akin to sharing a synchronized coin flip, where the second person to flip their coin will always see the opposite of what the first person sees, but neither has any way of knowing whether they were the first or second flipper, without communicating classically. See No-communication theorem for further information. A 2008 quantum physics experiment also performed by Nicolas Gisin and his colleagues has determined that in any hypothetical non-local hidden-variable theory, the speed of the quantum non-local connection (what Einstein called "spooky action at a distance") is at least 10,000 times the speed of light.

Delayed choice quantum eraser

Main article: Delayed-choice quantum eraser

The delayed-choice quantum eraser is a version of the EPR paradox in which the observation (or not) of interference after the passage of a photon through a double slit experiment depends on the conditions of observation of a second photon entangled with the first. The characteristic of this experiment is that the observation of the second photon can take place at a later time than the observation of the first photon, which may give the impression that the measurement of the later photons "retroactively" determines whether the earlier photons show interference or not, although the interference pattern can only be seen by correlating the measurements of both members of every pair and so it cannot be observed until both photons have been measured, ensuring that an experimenter watching only the photons going through the slit does not obtain information about the other photons in an faster-than-light or backwards-in-time manner.

Superluminal communication

Main article: Superluminal communication

Faster-than-light communication is, according to relativity, equivalent to time travel. What is measured as the speed of light in vacuum (or near vacuum) is actually the fundamental physical constant c. This means that all inertial and, for the coordinate speed of light, non-inertial observers, regardless of their relative velocity, will always measure zero-mass particles such as photons traveling at c in vacuum. This result means that measurements of time and velocity in different frames are no longer related simply by constant shifts, but are instead related by Poincaré transformations. These transformations have important implications:

• The relativistic momentum of a massive particle would increase with speed in such a way that at the speed of light an object would have infinite momentum.
• To accelerate an object of non-zero rest mass to c would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time.
• Either way, such acceleration requires infinite energy.
• Some observers with sub-light relative motion will disagree about which occurs first of any two events that are separated by a space-like interval. In other words, any travel that is faster-than-light will be seen as traveling backwards in time in some other, equally valid, frames of reference, or need to assume the speculative hypothesis of possible Lorentz violations at a presently unobserved scale (for instance the Planck scale). Therefore, any theory which permits "true" FTL also has to cope with time travel and all its associated paradoxes, or else to assume the Lorentz invariance to be a symmetry of thermodynamical statistical nature (hence a symmetry broken at some presently unobserved scale).
• In special relativity the coordinate speed of light is only guaranteed to be c in an inertial frame; in a non-inertial frame the coordinate speed may be different from c. In general relativity no coordinate system on a large region of curved spacetime is "inertial", so it is permissible to use a global coordinate system where objects travel faster than c, but in the local neighborhood of any point in curved spacetime there can be defined a "local inertial frame" and the local speed of light will be c in this frame, with massive objects moving through this local neighborhood always having a speed less than c in the local inertial frame.

Justifications

Casimir vacuum and quantum tunnelling

Special relativity postulates that the speed of light in a vacuum is invariant in inertial frames. That is, it will be the same from any frame of reference moving at a constant speed. The equations do not specify any particular value for the speed of light, which is an experimentally determined quantity for a fixed unit of length. Since 1983, the SI unit of length (the meter) has been defined using the speed of light.

The experimental determination has been made in a vacuum, but the observed vacuum is not the only possible vacuum which can exist. The vacuum has energy associated with it, called simply the vacuum energy, which could perhaps be altered in certain cases. When vacuum energy is lowered, light itself has been predicted to go faster than the standard value c. This is known as the Scharnhorst effect. Such a vacuum can be produced by bringing two perfectly smooth metal plates together at near atomic diameter spacing. It is called a Casimir vacuum. Calculations imply that light will go faster in such a vacuum by a minuscule amount: a photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 10³⁶. Accordingly, there has as yet been no experimental verification of the prediction. A recent analysis argued that the Scharnhorst effect cannot be used to send information backwards in time with a single set of plates since the plates' rest frame would define a "preferred frame" for FTL signaling. However, with multiple pairs of plates in motion relative to one another the authors noted that they had no arguments that could "guarantee the total absence of causality violations", and invoked Hawking's speculative chronology protection conjecture which suggests that feedback loops of virtual particles would create "uncontrollable singularities in the renormalized quantum stress-energy" on the boundary of any potential time machine, and thus would require a theory of quantum gravity to fully analyze. Other authors argue that Scharnhorst's original analysis, which seemed to show the possibility of faster-than-c signals, involved approximations which may be incorrect, so that it is not clear whether this effect could actually increase signal speed at all.

It was later claimed by Eckle et al. that particle tunneling does indeed occur in zero real time. Their tests involved tunneling electrons, where the group argued a relativistic prediction for tunneling time should be 500–600 attoseconds (an attosecond is one quintillionth (10⁻¹⁸) of a second). All that could be measured was 24 attoseconds, which is the limit of the test accuracy. Again, though, other physicists believe that tunneling experiments in which particles appear to spend anomalously short times inside the barrier are in fact fully compatible with relativity, although there is disagreement about whether the explanation involves reshaping of the wave packet or other effects.

Give up (absolute) relativity

Because of the strong empirical support for special relativity, any modifications to it must necessarily be quite subtle and difficult to measure. The best-known attempt is doubly special relativity, which posits that the Planck length is also the same in all reference frames, and is associated with the work of Giovanni Amelino-Camelia and João Magueijo. There are speculative theories that claim inertia is produced by the combined mass of the universe (e.g., Mach's principle), which implies that the rest frame of the universe might be preferred by conventional measurements of natural law. If confirmed, this would imply special relativity is an approximation to a more general theory, but since the relevant comparison would (by definition) be outside the observable universe, it is difficult to imagine (much less construct) experiments to test this hypothesis. Despite this difficulty, such experiments have been proposed.

Spacetime distortion

Although the theory of special relativity forbids objects to have a relative velocity greater than light speed, and general relativity reduces to special relativity in a local sense (in small regions of spacetime where curvature is negligible), general relativity does allow the space between distant objects to expand in such a way that they have a "recession velocity" which exceeds the speed of light, and it is thought that galaxies which are at a distance of more than about 14 billion light-years the Earth today have a recession velocity which is faster than light. Miguel Alcubierre theorized that it would be possible to create a warp drive, in which a ship would be enclosed in a "warp bubble" where the space at the front of the bubble is rapidly contracting and the space at the back is rapidly expanding, with the result that the bubble can reach a distant destination much faster than a light beam moving outside the bubble, but without objects inside the bubble locally traveling faster than light. However, several objections raised against the Alcubierre drive appear to rule out the possibility of actually using it in any practical fashion. Another possibility predicted by general relativity is the traversable wormhole, which could create a shortcut between arbitrarily distant points in space. As with the Alcubierre drive, travelers moving through the wormhole would not locally move faster than light travelling through the wormhole alongside them, but they would be able to reach their destination (and return to their starting location) faster than light traveling outside the wormhole.

Gerald Cleaver and Richard Obousy, a professor and student of Baylor University, theorized that manipulating the extra spatial dimensions of string theory around a spaceship with an extremely large amount of energy would create a "bubble" that could cause the ship to travel faster than the speed of light. To create this bubble, the physicists believe manipulating the 10th spatial dimension would alter the dark energy in three large spatial dimensions: height, width and length. Cleaver said positive dark energy is currently responsible for speeding up the expansion rate of our universe as time moves on.

Lorentz symmetry violation

Main articles: Modern searches for Lorentz violation and Standard-Model Extension

The possibility that Lorentz symmetry may be violated has been seriously considered in the last two decades, particularly after the development of a realistic effective field theory that describes this possible violation, the so-called Standard-Model Extension. This general framework has allowed experimental searches by ultra-high energy cosmic-ray experiments and a wide variety of experiments in gravity, electrons, protons, neutrons, neutrinos, mesons, and photons. The breaking of rotation and boost invariance causes direction dependence in the theory as well as unconventional energy dependence that introduces novel effects, including Lorentz-violating neutrino oscillations and modifications to the dispersion relations of different particle species, which naturally could make particles move faster than light.

In some models of broken Lorentz symmetry, it is postulated that the symmetry is still built into the most fundamental laws of physics, but that spontaneous symmetry breaking of Lorentz invariance shortly after the Big Bang could have left a "relic field" throughout the universe which causes particles to behave differently depending on their velocity relative to the field; however, there are also some models where Lorentz symmetry is broken in a more fundamental way. If Lorentz symmetry can cease to be a fundamental symmetry at the Planck scale or at some other fundamental scale, it is conceivable that particles with a critical speed different from the speed of light be the ultimate constituents of matter.

In current models of Lorentz symmetry violation, the phenomenological parameters are expected to be energy-dependent. Therefore, as widely recognized, existing low-energy bounds cannot be applied to high-energy phenomena; however, many searches for Lorentz violation at high energies have been carried out using the Standard-Model Extension. Lorentz symmetry violation is expected to become stronger as one gets closer to the fundamental scale.

Superfluid theories of physical vacuum

Main article: Superfluid vacuum theory

In this approach, the physical vacuum is viewed as a quantum superfluid which is essentially non-relativistic, whereas Lorentz symmetry is not an exact symmetry of nature but rather the approximate description valid only for the small fluctuations of the superfluid background. Within the framework of the approach, a theory was proposed in which the physical vacuum is conjectured to be a quantum Bose liquid whose ground-state wavefunction is described by the logarithmic Schrödinger equation. It was shown that the relativistic gravitational interaction arises as the small-amplitude collective excitation mode whereas relativistic elementary particles can be described by the particle-like modes in the limit of low momenta. The important fact is that at very high velocities the behavior of the particle-like modes becomes distinct from the relativistic one – they can reach the speed of light limit at finite energy; also, faster-than-light propagation is possible without requiring moving objects to have imaginary mass.

FTL neutrino flight results

MINOS experiment

Main article: MINOS

High precision measurements from the MINOS collaboration for the flight-time of 3 GeV neutrinos yielded a speed (v/c−1)=(1.0±1.1)×10⁻⁶, that is equal to the speed of light to one part in a million.

OPERA neutrino anomaly

Main article: Faster-than-light neutrino anomaly

On September 22, 2011, a preprint from the OPERA Collaboration indicated detection of 17 and 28 GeV muon neutrinos, sent 730 kilometers (454 miles) from CERN near Geneva, Switzerland to the Gran Sasso National Laboratory in Italy, traveling faster than light by a relative amount of 2.48×10⁻⁵ (approximately 1 in 40,000), a statistic with 6.0-sigma significance. On 17 November 2011, a second follow-up experiment by OPERA scientists confirmed their initial results. However, scientists were skeptical about the results of these experiments, the significance of which was disputed. In March 2012, the ICARUS collaboration failed to reproduce the OPERA results with their equipment, detecting neutrino travel time from CERN to the Gran Sasso National Laboratory indistinguishable from the speed of light. Later the OPERA team reported two flaws in their equipment set-up that had caused errors far outside their original confidence interval: a fiber-optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast.

Tachyons

Main article: Tachyon

In special relativity, it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light. However, it might be possible for an object to exist which always moves faster than light. The hypothetical elementary particles with this property are called tachyons or tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability.

Various theorists have suggested that the neutrino might have a tachyonic nature, while others have disputed the possibility.

General relativity

General relativity was developed after special relativity to include concepts like gravity. It maintains the principle that no object can accelerate to the speed of light in the reference frame of any coincident observer. However, it permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer. One such distortion is the Alcubierre drive, which can be thought of as producing a ripple in spacetime that carries an object along with it. Another possible system is the wormhole, which connects two distant locations as though by a shortcut. Both distortions would need to create a very strong curvature in a highly localized region of space-time and their gravity fields would be immense. To counteract the unstable nature, and prevent the distortions from collapsing under their own 'weight', one would need to introduce hypothetical exotic matter or negative energy.

General relativity also recognizes that any means of faster-than-light travel could also be used for time travel. This raises problems with causality. Many physicists believe that the above phenomena are impossible and that future theories of gravity will prohibit them. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality would result in their decay. In string theory, Eric G. Gimon and Petr Hořava have argued that in a supersymmetric five-dimensional Gödel universe, quantum corrections to general relativity effectively cut off regions of spacetime with causality-violating closed timelike curves. In particular, in the quantum theory a smeared supertube is present that cuts the spacetime in such a way that, although in the full spacetime a closed timelike curve passed through every point, no complete curves exist on the interior region bounded by the tube.

Psychiatric genetics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Psychiatric_genetics 

Psychiatric genetics is a subfield of behavioral neurogenetics and behavioral genetics which studies the role of genetics in the development of mental disorders (such as alcoholism, schizophrenia, bipolar disorder, and autism). The basic principle behind psychiatric genetics is that genetic polymorphisms (as indicated by linkage to e.g. a single nucleotide polymorphism) are part of the causation of psychiatric disorders.

Psychiatric genetics is a somewhat new name for the old question, "Are behavioral and psychological conditions and deviations inherited?". The goal of psychiatric genetics is to better understand the causes of psychiatric disorders, to use that knowledge to improve treatment methods, and possibly also to develop personalized treatments based on genetic profiles (see pharmacogenomics). In other words, the goal is to transform parts of psychiatry into a neuroscience-based discipline.

Recent advances in molecular biology allowed for the identification of hundreds of common and rare genetic variations that contribute to psychiatric disorders.

Psychiatric genetics has established that most psychiatric disorders, such as schizophrenia and autism, are highly heritable and polygenic, meaning they are influenced by thousands of common genetic variants, each having a small effect on risk.

History

Research on psychiatric genetics began in the late nineteenth century with Francis Galton (a founder of psychiatric genetics) who was motivated by the work of Charles Darwin and his concept of desegregation. These methods of study later improved due to the development of more advanced clinical, epidemiological, and biometrical research tools. Better research tools were the precursor to the ability to perform valid family, twin, and adoption studies. Researchers learned that genes influence how these disorders manifest and that they tend to aggregate in families. Major recent progress in psychiatric genetics has been made possible by the advent of the 'genome-wide association study', a case-control design that compares genetic variants in very large groups of individuals with and without a diagnosis, and through large, global collaborative efforts including the wellcome trust case control consortium and psychiatric genomics consortium, among many others.

Heritability and genetics

Most psychiatric disorders are highly heritable; the estimated heritability for bipolar disorder, schizophrenia, and autism (80% or higher) is much higher than that of diseases like breast cancer and Parkinson's disease. Having a close family member affected by a mental illness is the largest known risk factor, to date. However, linkage analysis and genome-wide association studies have found few reproducible risk factors.

Heterogeneity is an important factor to consider when dealing with genetics. Two types of heterogeneity have been identified in association with psychiatric genetics: causal and clinical. Causal heterogeneity refers to a situation in which two or more causes can independently induce the same clinical syndrome. Clinical heterogeneity refers to when a single cause can lead to more than one clinical syndrome.

Several genetic risk factors have been found with the endophenotypes of psychiatric disorders, rather than with the diagnoses themselves. That is, the risk factors are associated with particular symptoms, not with the overall diagnosis. In psychiatry, endophenotypes are a way of objectively measuring certain internal processes in a reliable way that is often lacking the diseases with which they are associated. They lie in the space between genes and disease process and allow for some understanding of the biology of psychiatric diseases.

A systematic comparative analysis of shared and unique genetic factors highlighted key gene sets and molecular processes underlying six major neuropsychiatric disorders: attention deficit hyperactivity disorder, anxiety disorders, autistic spectrum disorders, bipolar disorder, major depressive disorder, and schizophrenia. This may ultimately translate into improved diagnosis and treatment of these debilitating disorders.

Methodology

Linkage, association, and microarray studies generate raw material for findings in psychiatric genetics. Copy number variants have also been associated with psychiatric conditions.

Genetic Linkage studies attempt to find a correlation between the diagnosis and inheritance of certain alleles within families who have two or more ill relatives. An analysis of a linkage study uses a wide chromosomal region, whereas a genetic association study endeavors to identify a specific DNA polymorphism, which can be a deletion, inversion, or repletion of a sequence. Case-control association studies can be used as an exploratory tool for narrowing the area of interest after preliminary mapping of a gene by a linkage study.

Genome-Wide Association Studies uncover genetic links in psychiatric disorders by analyzing the genomes of large groups of individuals, comparing genetic variants between individuals with a disorder and individuals without to identify regions associated with increased risk.

Predictive genetic testing

One hope for future genetic testing is the ability to test for presymptomatic or prenatal illnesses. This information has the potential to improve the lives of those affected with certain illnesses, specifically those like schizophrenia. If possible to test for schizophrenia before the symptoms develop, proactive interventions could be developed, or even preventative treatments. In one study, 100% of patients with bipolar disorder indicated that they would probably take a genetic test to determine they were carrying a gene associated with the disorder, if such a test existed.

Ethical issues

Francis Galton studied both desirable and undesirable behavioral and mental properties to better examine the world of genetics. His research led to his proposal of a eugenic program of birth control. His goal was to decrease the frequency of the less desirable traits that occurred throughout the population. His ideas were pursued by psychiatrists in many countries such as the United States, Germany and Scandinavia.

Genotyping and its implications are still seen as ethically controversial by many people. The ELSI (Ethical, Legal, and Social Initiative), which is part of the Human Genome Project, was created with the aim of "foster[ing] basic and applied research on the ethical, legal and social implications of genetic and genomic research for individuals, families and communities.".

Psychiatric Genetic Disorders

For many years, it was known and accepted that there were genetic linkages between psychiatric disorders and a person’s predisposition to the disorder, but only in the past few years has there really been an effort made to identify any specific genes or markers leading to disorders such as schizophrenia, ASD, bipolar disorder, and anxiety disorders. In a recent analysis, a group studied the genetic architecture of these mental illnesses at several levels of analysis. The method of analysis in this case was genomic structural equation modeling on genome-wide association studies (GWAS).  GWAS is a genetic tool that scans the entire DNA to identify pieces of the DNA associated with certain diseases or syndromes. With this data, scientists were able to sort 11 disorders into clustered groups and establish a covariance structure. They identified four correlational groups, sorting the different disorders into genetically similar sections thatbest fit the data. Factor 1 (or Group 1) consisted of anorexia nervosa, OCD, and Tourette syndrome, which were all categorized as compulsive behavior. Factor 2 involved disorders with psychotic features (schizophrenia and bipolar disorder), Factor 3 included ADHD and autism, and Factor 4 contained anxiety and major depressive disorder. These factors consisted of childhood-onset neurodevelopmental disorders and internalizing disorders, respectively. Based on various data collection, correlational studies, and computing, the groups ultimately found varying numbers of independent loci for each factor, noting 154 total hits. Independent loci are specific locations, or markers, in chromosomes that are inherited independently of each other. Eighty-nine of these independent loci were found in correlation with the psychotic disorders, highlighting 12 new loci. The internalizing disorders had 29 genome-wide significant loci identified, while the neurodevelopmental group had 8, and the compulsive disorder factor only had one major hit. Additionally, two specific markers were found: SNP rs9314056 (seen in the internalizing factor as a hit for MDD and anxiety) andthe ADH1B gene (rs4699743, seen in all four factors, although it was linked specifically with the idea that alcohol use may causally influence psychiatric risk.  

In another study, which was more interested in the identification of therapeutic treatments of mental disorders, they detailed shared pathways and genetic factors involved in overlapping and similar illnesses. While expanding on the shared pathways between neurological and mental diseases, the article introduced the idea of genetic pleiotropy, where a single gene “affects numerous phenotypic features that may appear unrelated.” One example of this is theCACNA1C gene, which has been discovered to be a risk factor for bipolar disorder, as well as migraines and epilepsy.  

An article from World Psychiatry gives a solid overview of biomarkers for many of the previously mentioned mental disorders. It begins with autism spectrum disorder, which, as of 2023, has the most genes identified as markers of any other DSM diagnosis. The article cited another study from Jakob Grove, a professor in the Department of Biomedicine at Aarhus University, and his team, for several identified loci of autism spectrum disorder, including the NEGR1, PTBP2, CADPS, KCNN2, KMT2E, and MACROD2 genes. Anxiety disorders were discussed next, highlighting the COMT (rs4680, G [val] allele), NPSR1 (rs324981, T allele), TPH1 (rs1800532, AA genotype), HTR2A (rs6313, T allele), and MAOA (uVNTR, long alleles) genes to be involved through their own gene study. Along with this, GWAS was used to note the several SNPs within the ESR1, GLRB, MYH15, NTRK2, PDE4B, RBFOX1, SATB1, TMEM132D, and TMEM106B genes, which are linked to anxiety disorders and anxiety-related traits. SNPs refer to single-nucleotide polymorphisms, which is when a single base in the DNA is changed. Finally, the article by World Psychiatry touched on the presence of the genetic markers behind mood disorders, stating that GWAS found 17 new loci for those disorders that fall in line with previously done secondary post-mortem studies.

These studies are constantly evolving, aiming to connect mental disorders with subsequent affecting genes in an effort to better understand underlying causes, early risk determinants, and possible courses of treatment. While not every aspect is understood yet, and not all markers have been identified, genetic psychiatry has made leaps and bounds from where it was even 10 years ago and continues to work towards not only the identification of these markers but potentially being able to alter them.

Discrimination against autistic people

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Discrimination_against_autistic_people 

Discrimination against autistic people involves any form of discrimination, persecution, or oppression against autistic people. Autistic people face discrimination of various kinds, both directly and indirectly, extending into a variety of settings such as the professional, educational, and clinical. Such discrimination is often initiated after other people identify the autistic person as being different from themselves, which may occur very quickly. Discrimination oftentimes presents together with associated phenomena, such as violence, assault, and social exclusion. Discrimination against autistic people is also considered a form of ableism.

Prevalence

Ireland

In 2021, Adam Harris of AsIAm said that class was a factor in reluctance of schools in wealthy areas to enrol students with special needs. He was speaking to an Oireachtas committee on education. Campaigners there called for the Education of Persons with Special Needs (Espen) Act to be fully implemented. Harris said that recent attempts to make schools in South Dublin open special needs classes resulted in most new classes being in less wealthy areas, with few in Dublin 2, Dublin 4, Dublin 6 or Dublin 6W. He said there appeared to be a "hierarchy of rights" in some wealthy schools which were open to expanding facilities for existing pupils but were against enrolling autistic pupils. He said "What they are arguing is that they have an obligation to some pupils , but that is negated if they had a disability".

Research published by charity AsIAm in 2022 showed that 6 in 10 Irish people associated autism with negatively perceived characteristics such as "not making eye contact", "difficulty making friends" and "no to little verbal communication". People were less likely to know the positive traits associated with autism, such as logical thinking, honesty and being detail-oriented. The survey found that 10% of autistic people surveyed felt workplaces were inclusive.

The Same Chance report was based on two surveys conducted on behalf of AsIAm – the first, by Core Research, assessed public attitudes toward autistic people by surveying 1,000 members of the general public. The second survey was of 944 parents, carers, and autistic people over the age of 18.

The issues raised in the second survey included accessing healthcare, education, employment, and housing.

United Kingdom

Research published in 2019 used data from more than 8,000 children in the University of London's Millennium Cohort Study, which tracks the lives of about 19,000 people born in the United Kingdom starting in 2000. Out of the children selected, 231 were autistic. The study from the Journal of Autism and Developmental Disorders found that these autistic children were more likely to engage in "two-way sibling bullying", meaning being both a victim and perpetrator of bullying.

Further research published in 2017, a meta-analysis of three studies, demonstrated that "first impressions of individuals with ASD made from thin slices of real-world social behavior by typically-developing observers are not only far less favorable across a range of trait judgments compared to controls, but also are associated with reduced intentions to pursue social interaction." The meta-analysis continues, "These patterns are remarkably robust, occur within seconds, do not change with increased exposure, and persist across both child and adult age groups." This may be why autistic people have "smaller social networks and fewer friendships, difficulty securing and retaining employment, high rates of loneliness, and an overall reduced quality of life." Smaller social networks, fewer friendships, and loneliness correlate with severe negative health outcomes. According to a paper published in the Journal of Health and Social Behavior, "Health risks associated with social isolation have been compared in magnitude to the well-known dangers of smoking cigarettes and obesity." Furthermore, according to the UK Office for National Statistics, the unemployment rate of autistic people may reach 85%, the highest rate among all disabled groups studied. It is noted that in many countries, autism is not a disability protected by anti-discrimination employment laws, and this is due to many corporations lobbying against it. Autistic adults are also more likely to face healthcare disparities, such as being unvaccinated against common diseases like tetanus and being more likely to use emergency services.

Autistic people are also less likely to graduate from secondary school, college, or other forms of higher education, further contributing to high rates of unemployment and lower quality of life. This failure to complete education can be in part attributed to a lack of support from educational institutions. In the UK, only one quarter of autistic children in state-funded schools feel happy and are thus able to achieve their maximum potential.

United States

In the United States, disabled people are victims of violent crime three times as often as non-disabled people. The Bureau of Justice Statistics does not report separately on autistic victims, but it does note that the victimization rate is especially high among those whose disabilities are cognitive. A small-sample study of Americans and Canadians found that autistic adults face a greater risk of sexual victimization than their peers. Autistic respondents were more than twice as likely to say they had been the victim of rape and over three times as likely to report unwanted sexual contact. In 2018, a large scale study found that autistic girls were almost three times more likely to be a victim of sexual abuse compared to non-autistic girls.

Discrimination in media and culture

Representation of autistic people in media has perpetuated myths about autism, including characterizing autism as shameful and burdensome for family members, advertising fake cures for autism, and publicizing the long-disproven arguments surrounding vaccines and autism. These myths are perpetuated in mass media, news media, and social media. Stigmatization of autism can also be perpetuated by advertising from autism conversion organizations, such as Autism Speaks' advertising wherein Alison Singer describes having considered murder-suicide in front of her autistic daughter or the NYU Child Study Center's advertisements where autism is personified as a kidnapper holding children for ransom.

Moreover, stimming in autistic people, which is often more intense than in non-autistic people, is frequently referred to as "distracting". Conversational tones and behaviors seen in many autistic people are often described as "rude". Stimming specifically is often targeted in therapies such as applied behavior analysis, even though it is vital to self regulation.

Physical health-related research

In the United States, recently published research shows that the National Institutes of Health (NIH) has not funded grants focused on the treatment of physical health disparity conditions, such as insomnia, cardiovascular disease, and other conditions, in autistic adults across four decades of research funding. McDonald and Scudder (2023) explicitly distinguish health-disparity conditions that affect the lives of autistic people from research grants focused on the cause, "cure", and prevention of autism. Although their research focused on autistic adults without an intellectual disability, the research did not exclude this population and found a lack of funded grants focused on the treatment of health disparity conditions for intellectually disabled autistic adults. The research describes several systemic discriminatory "nodes" of practices and policies that may contribute to the apparent discrimination in research grant funding. These include the exclusion of disability populations from groups designated for physical health disparity research grants, the designation of autism as a "primary disease;" a designation used as a rationale for some National Institutes of Health (e.g., the National Heart, Lung, and Blood Institute) to exclude research focused on autistic populations from grant funding review, and the pressure on early career researchers by academic institutions (that receive NIH funding) to either change their research topic or their population for NIH grant applications and to avoid challenging NIH policies until they are at a more advanced stage in their career.

Immigration

In the United States, the first Trump administration supported restrictive immigration policies that discriminated against autistic people. Under these policies, autistic immigrants faced deportation.

In Canada, autistic immigrants have been denied citizenship, or they have faced deportation due to the perception that they are a "burden" upon the Canadian medical system. In 2018, reforms in Canadian immigration law were announced – these reforms are supposed to make it easier for autistic and disabled immigrants to migrate to Canada.

New Zealand effectively prohibits the application for permanent residency for autistic people "where significant support is required".

Australia's health criteria have prompted criticism about its immigration policies. Australia forbids the immigration of people who would be exceptionally costly for the nation's health care or social services. Autistic people are subject to this policy.

Violence and autism

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Violence_and_autism

Various connections have been made between violence and autism within social narratives. According to public opinion, violent behavior is common for autistic individuals, but evidence does not support autism spectrum disorder (ASD) as a predisposition to delinquency or crime. In fact, autistic people are more likely to be victims of bullying, abuse, and other violence.

Violence against autistic people

14-year-old autistic adolescent girl in sensory withdrawal (or shutdown)

Autistic individuals are often victims of violence, including bullying, abuse, sexual assault and criminal acts. Violence can be physical or verbal, as illustrated by the frequent use of the word "autistic" as an insult. Autistic people, like many disabled people, are often victims of hate crimes, and many live in fear.

A 2003 study found that children diagnosed with Asperger syndrome (a since-defunct autism subtype) were more likely to be victims of violence than tormentors. Violence against non-speaking autistic people is also facilitated by the fact that they are unable to talk about it and report it: in general, the more a person is considered to be "in a weak situation", or as a "severe" case, the more vulnerable they are to violence and social exclusion. Dependence is an aggravating factor, especially if daily assistance is required for everyday activities such as meals and washing. The "seriousness" of the "disability" can thus be invoked to justify all types of violence, including murder.

In schools

Bullying is "the most common form of violence among children and adolescents", according to Park, et al. (2020). Autistic students are victims more often than other students; the prevalence of being victimized is higher than being a perpetrator of bullying.

In the family environment

The changeling myth was once used to justify the abandonment and murder of autistic babies and children by their biological families.

Familial abuse against autistic children does not appear to be more frequent than familial abuse against non-autistic children.

However, cases of infanticide, usually committed by the mother of the autistic child, have been documented. Dozens of murders have been reported in the Western press over the past decade, particularly in the Canadian press. Each murder case is treated individually, but the general motive given for each is "autism" or "living with autism". Testimony on this subject emphasizes the supposed severity of autism and the despair it is thought to generate.

A form of extreme violence, the murder of autistic people by their relatives, is justified by the bad public perception of autism, assimilated to a "lifelong pathology" that should be fought. Some of this violence results from the medical model of autism, which promotes a vision of autism as a disease to be eradicated or an abnormality to be normalized. The extreme violence is illustrated by the accounts of murderers who want to "kill autism" in the hope of making their loved ones "normal".

Social class seems to be a predisposing factor to murder, as the infanticidal mothers did not have the financial resources to receive effective support for their disabled child.

Violence caused by autistic people

According to Anne-Sophie Ferry, "Autism is not characterized by violence or outbursts of anger", though the latter sometimes results from communication difficulties or accumulated distress. Institutionalized non-speaking autistic adolescents may express violent behaviors such as spitting or biting, without understanding their actions.

Some behavioral characteristics of autistic people are wrongly interpreted as violence by those around them, including dislike of physical contact, lack of eye contact, and lack of response to parents' voices. Non-speaking autistic people may have inappropriate behavior in terms of force and impact on the other person, leading them to be characterized as violent behaviors.

Furthermore, autistic people's sensory hypersensitivities can trigger reactions that are perceived as violent. Autistic individuals may attempt to cope with sensory overload by impulsively releasing it through actions such as avoidance or clawing gestures, often without considering the potential for violence; this violence is not intended to harm others but rather as an effort to regulate their sensory experiences.

Criminal and delinquent behavior

No evidence exists suggesting an association between autism and delinquency, and the delinquency rate is lower among autistic individuals than among non-autistic individuals.

Individual cases of autistic criminals do not provide generalization of a predisposition to violence to the entire autistic community.

A psychological profile of two mass murderers sometimes considered autistic, Adam Lanza and Anders Behring Breivik, found that their actions were not explained by autism alone but rather by the intertwining of various factors, including the association between ASD and narcissistic personality disorder, which forms "a particularly 'explosive' combination that increases the risk that an autistic individual may engage in extremely violent behavior". Anders Breivik was diagnosed with Asperger syndrome, narcissistic personality disorder, and antisocial personality disorder.

Jeffrey Dahmer, a cannibalistic and necrophiliac serial murderer, was retrospectively diagnosed with Asperger syndrome in 2002, but the accuracy of that speculative diagnosis has been questioned. Mass murderer Dylann Roof was diagnosed with autistic traits and, possibly, ASD by forensic psychiatrist James Ballenger. However, similar to Dahmer's case, Roof's diagnosis has been questioned and even rejected by Roof himself, who said that he "would rather die than be labeled as autistic or mentally ill."

Social perception

Autism is associated with inappropriate behaviors, such as violence, delinquency, crime (including mass killing) in the English, French, and German media.

Robert Chapman argued in 2017 that a bias exists in the way information about violence in autism is processed: violence experienced against non-autistic people from autistic people may receive more attention, whereas violence experienced by autistic people is invisible, or considered "normal", leading to "a collective cultural failure to recognize violence against autistic people as a significant and pressing socio cultural issue".

Media portrayals of autism and violence negatively influence public opinion on autism and foster negative impressions of autistic people by linking autism with criminal behavior. For example, an analysis of 100 French and Italian works of children's and young people's literature published between 1995 and 2005 featuring a main disabled character found that autistic people are presented as violent. The film The Specials has a line that autism educators "take a beating all day". The American film The Accountant (2016), which features an obsessive, unempathetic autistic accountant operating as a contract killer, has been called offensive to autistic people, in part because of the violence it exhibits.

Beyond fictional characterizations, news sources may perpetuate the connection between autism and violence. For instance, Adam Lanza was immediately labeled as autistic in the French media on December 14, 2012. Individual cases of autistic people versed in cybercrime and terrorism have also been documented in the press.

Activists for the rights of autistic people oppose the media's tendency to link autism and violence, arguing that social discrimination is already a source of suffering for this population. Activists began to document acts of violence committed against autistic people in the 2000s, calling for a political response.