More on this book
Community
Kindle Notes & Highlights
In this quantum state they can exhibit all the weird quantum behaviors, such as being in two places at once, spinning in two directions at once, tunneling through impenetrable barriers or possessing spooky entangled connections with a distant partner.
In this way we can think of decoherence as the means by which all the material surrounding any given atom, say—what is referred to as its environment—is constantly measuring that atom and forcing it to behave like a classical particle.
In fact, to demonstrate interference patterns with single atoms, scientists pump all the air out of the apparatus and cool their equipment down to very close to absolute zero. Only by taking these extreme steps can they maintain their atoms in a quiet quantum coherent state for long enough to demonstrate the interference patterns.
So the idea that quantum coherence could be maintained in the hot, wet and molecularly turbulent environment inside a blade of grass was understandably thought to be crazy.
The watery fluid filling the cell, known as the cytoplasm, is thick and viscous; in places it’s more like a gel than a liquid.
These are protein enzymes, like those we met in the last chapter, responsible for conducting the cells’ metabolic processes, breaking down nutrients and making biomolecules such as carbohydrates, DNA, protein and fats.
Both need electrons to build biomolecules: we burn organic molecules to capture their electrons, while plants use light to burn water to capture its electrons.
Life seems to bridge the quantum and classical worlds, perched on the quantum edge.
Unlike our senses of sight and hearing, which capture information indirectly via electromagnetic waves or sound waves carried to us from an object, both taste and smell receive information directly from contact with the object detected (a molecule), bringing messages “from a material reality.
Your next inhalation will suck in several liters of this odorant-laden air that will pass through your nostrils and across the nasal epithelium, which is lined with approximately ten million olfactory neurons.
The capturing of a single limonene molecule is sufficient to trigger the opening of a tiny channel in the neuron’s cell membrane that allows a flow of positively charged calcium ions into the cell from outside. When about thirty-five limonene molecules have been captured, the subsequent flow of ions into the cell amounts to a tiny electric current of about one picoamp*5 in total.
It seemed that each olfactory neuron was not a generalist but a specialist.
They discovered that each odorant chemical activated not just one but several neurons; also, that single neurons responded to several different odorants.
But how does each receptor recognize its own set of odorant molecules, such as limonene, and not capture and bind to any one of the chemical ocean of other possible odorants that might float past the olfactory epithelium? This is the central mystery of smell.
Dyson went on to propose that what the nose detects is not the shape of an entire molecule but rather a different physical feature, namely the frequency at which the molecular bonds between its atoms vibrate.
In inelastic scattering, photons similarly lose energy to the molecular bonds they bump into, causing them to vibrate; the scattered light therefore emerges with less energy.
Reducing the energy of light lowers its frequency and shifts its color toward the blue end of the spectrum, providing Raman with his “wonderful blue opalescence.
Thus, neither odotope nor vibration theory can explain how pairs of chemicals can have different odors despite possessing the same chemical groups arranged differently on the same molecular scaffold.
Considered classically, the electrons lack the energy to jump across the insulating gap between the plates; but electrons are quantum objects and, if the gap is small enough, they can quantum tunnel across from donor to acceptor. This process is called elastic tunneling because the electrons do not gain or lose energy in the process.
If the nearest available gap in the acceptor is at lower energy, then the electron must lose some of its energy to make the jump. This process is called inelastic tunneling. But the dumped energy needs to go somewhere, otherwise the electron can’t tunnel. If a chemical is placed in the gap between the plates, then an electron can tunnel across so long as it is able to donate its excess energy to the chemical—which it can do so long as the molecules in the gap have bonds capable of vibrating at just the right frequency, corresponding to that of the dumped energy.
Turin proposed that the tunneled electron, now sitting in the acceptor site, causes the release of the tethered G protein molecular torpedo, causing the olfactory neuron to fire and thereby send a signal off toward the brain, allowing us to “experience” the scent of the orange.
Only after either odorant has fitted into its complementary receptor does it have the potential to stimulate the vibration-induced electron tunneling event to make the receptor neuron fire; but because the left-handed molecule will be firing a left-handed receptor, it will smell different from a right-handed molecule firing a right-handed receptor.
So although limonene and dipentene have the same vibrations, they have to be held by left- or right-handed olfactory receptors. The different receptors will be wired to different regions of the brain and will thereby generate different smells.
No experiment has yet directly tested whether quantum tunneling is involved in smell.
So, although considerable controversy remains, the only theory that provides an explanation of how flies and humans can distinguish the smells of normal and deuterated compounds is based on the quantum mechanical mechanism of inelastic electron tunneling.
Like us, fruit flies adjust their circadian rhythms to the cycles of light and dark.
Just like in photosynthesis, the light absorption knocks an electron out of the pigment, which leads to the generation of a signal that travels to the fly’s brain to keep its body’s clock in synch with the daily light–dark cycle.
Reppert wondered whether the cryptochrome that provided flies with the light sensitivity that helped to entrain their circadian rhythms could also be involved in their magnetoreception sense.
several researchers have since established beyond reasonable doubt that a wide range of animals have an inbuilt sensitivity to the earth’s magnetic field, giving them an acute sense of direction.
Electrons can only—in a loose sense—spin in either a clockwise or a counterclockwise direction, corresponding to what is usually referred to as spin “up” or spin “down” states. And because this is the quantum world, an electron can, when not being watched, spin in both directions at the same time
One of the consequences of the Pauli Exclusion Principle is that if two electrons are paired up in an atom or molecule and have the same energy (remember from chapter 3 that the chemical bonds that hold molecules together are made up of electrons that are shared between atoms), then they have to have opposite spin. We can then think of their spins as canceling out, and we refer to them as being in a spin singlet state, since they can only inhabit a single state. This is the normal state of pairs of electrons in atoms and most molecules.
Its technical name is nonlocality, or entanglement, and it refers to the idea that something happening “over here” can have an instantaneous effect “over there” no matter how far away “there” is.
This bizarre feature of the quantum world seems not to respect Einstein’s cosmic speed limit, for a particle in one place can instantaneously influence another, however far apart the two may be.
But remember that pairs of electrons in the same atom are always in a singlet state, which means that they have to have opposite spin at all times: one must be spin-up and the other must be spin-down. So although both electrons are in a superposition of being both up and down at the same time, in a peculiar quantum way they must, at all times, have opposite spin.
If we then decide to measure the spin state of one electron we will force it to choose which way it is spinning.
So the second electron has instantly and remotely changed its physical state from being in a superposition of spinning both ways at once to being spin-down—without being touched.
If one electron from a singlet pair sitting in the same atom jumps across into a neighboring atom, its spin can flip over so that it is now spinning in the same direction as the twin it left behind, creating a triplet spin state. However, despite now being in different atoms, the pair can still maintain their delicate entangled state in which they remain quantum mechanically coupled together. But this is the quantum world, and just because the electron that jumped out of the atom can now flip its spin, this doesn’t mean that it definitely has. Each of the two electrons will still be in a
...more
You may recall that electronic bonds between atoms are often formed by the sharing of a pair of electrons. This electron pair is always entangled and almost always in a singlet spin state: that is, the electrons have opposite spin.
We have no idea what this magnetic “seeing” looks like to birds, but since cryptochrome is an eye pigment that is potentially doing a similar job to the opsin and rhodopsin pigments that provide color vision, perhaps the birds’ view of the sky is imbued with an extra color invisible to the rest of us (just as some insects can see ultraviolet light) that maps onto the earth’s magnetic field.
So a conventional compass may be disrupted by magnetic fields oscillating at low frequencies but not at high frequencies.
The results were astonishing: a magnetic field tuned to 1.3 MHz (that is, oscillating at 1.3 million cycles per second), thousands of times weaker than even the earth’s field, could nevertheless disrupt the birds’ ability to orientate themselves. But increasing or decreasing the frequency of the field made it less effective. So the field appeared to be resonating with something vibrating at very high frequencies in the avian compass: clearly not a conventional magnetite-based compass, but something consistent with an entangled radical pair in a superposition of singlet and triplet states.
So there are still aspects of the system that remain mysterious; for example, why the robin’s compass should be so hypersensitive to oscillating magnetic fields, and how free radicals can remain entangled for long enough to make a biological difference.
A study published by a Czech group in 2009 demonstrated magnetoreception in the American cockroach and showed that, as with the European robin, it was disrupted by high-frequency oscillating magnetic fields.
So quantum compasses are probably ancient, and are likely to have provided navigational skills for the reptiles and dinosaurs that roamed the Cretaceous swamps alongside the T. rex we met in chapter 3 (remember that modern birds such as robins are descended from dinosaurs), the fish that swam the Permian seas, the ancient arthropods that crawled over or burrowed beneath the Cambrian oceans and maybe even the pre-Cambrian microbes that were the ancestors of all cellular life.
The Swedish physicist Per-Olov Löwdin was the first to point out what seems obvious in hindsight: that the protons’ position is determined by quantum, not classical, laws. So the genetic code that makes life possible is inevitably a quantum code. Schrödinger was right: genes are written in quantum letters, and the fidelity of heredity is provided by quantum rather than classical laws.
In their second paper on the structure of DNA,4 Watson and Crick suggested that a process called tautomerization, which involves the movement of protons within a molecule, could also be a cause of mutation. As I am sure you are well aware by now, any process that involves the movement of fundamental particles, like protons, can be quantum mechanical.
It is important to emphasize that DNA mutations are caused by a variety of different mechanisms, including damage caused by chemicals, ultraviolet light, radioactive decay particles, even cosmic rays.
So when the DNA polymerase enzyme scans a DNA base to determine the position of coding protons, it is carrying out a quantum measurement, no different in principle from when a physicist measures the position of a proton in the laboratory.
We have explored many of these revelations in earlier chapters, but all those we have so far discussed, from magnetic compasses to enzyme action, from photosynthesis to heredity to olfaction, can be discussed in terms of conventional chemistry and physics.
The conscious mind is able to “seize” on complex information “with various parts” so that its meaning can be grasped “in its entirety.
