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If quantum physics states matter doesn't exist when it's not being noticed, then, without life, would the universe cease to exist? Answer by Viktor T. Toth , IT pro, part-time physicist, on Quora :. This question demonstrates the dangers of trying to comprehend modern physics from popularizations.

It is absolutely not true that states of matter do not exist when they are not noticed. If someone tells you this, he is talking nonsense. The correct statement is that a quantum system usually exists in a state that is not at all like the states of the classical world. Simply put, it cannot be described by ordinary numbers. This is in contrast with classical objects, which can be described with ordinary numbers.

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That is to say, their position, their velocity, and other physical properties can be described using simple numerical values. Now it is true that there is no such thing as a truly classical object: that even people, cats, cannonballs or planets are made of a large number of quantum particles. However, in these systems, all the quantum behavior is averaged out, so to speak, so their behavior is indistinguishable from that of classical systems.

Every once in a while, some properties of a quantum system may be describable by ordinary numbers. This is precisely what happens when a quantum system interacts with a classical system; i.

Garden of Cosmic Delights

During the interaction, the quantum system is confined to an eigenstate. Let me explain this through a common thought experiment: the infamous two-slit experiment. The experiment involves an electron gun that emits electrons which can go through one of two slits before impacting a screen. We find that an interference pattern emerges on the screen; this is true even when we fire the electrons one at a time. You may have heard that this means that every single electron goes through both slits. True, but there is a better way to understand this.


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En route, however, the electron is not in a position eigenstate. It does not have a position in the classical sense at all. So yes, it goes through both slits and does many other things that classical objects just cannot do and it is wrong even to try to visualize the electron when it is in this quantum state.

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There is a temptation to linger on a story like that, to wonder if there might be a deeper order behind a life so poetically bracketed. We are content to remind ourselves that the vast majority of lives are not so celestially attuned, and go about our business in the world. But some coincidences are more troubling, especially if they implicate larger swathes of phenomena, or the entirety of the known universe.

During the past several decades, physics has uncovered basic features of the cosmos that seem, upon first glance, like lucky accidents. Theories now suggest that the most general structural elements of the universe — the stars and planets, and the galaxies that contain them — are the products of finely calibrated laws and conditions that seem too good to be true. It can be unsettling to contemplate the unlikely nature of your own existence, to work backward causally and discover the chain of blind luck that landed you in front of your computer screen, or your mobile, or wherever it is that you are reading these words.

For you to exist at all, your parents had to meet, and that alone involved quite a lot of chance and coincidence. But that is only the tiniest tip of the iceberg. Even if your parents made a deliberate decision to have a child, the odds of your particular sperm finding your particular egg are one in several billion. The same goes for both your parents, who had to exist in order for you to exist, and so already, after just two generations, we are up to one chance in 10 Carrying on in this way, your chance of existing, given the general state of the universe even a few centuries ago, was almost infinitesimally small.

You and I and every other human being are the products of chance, and came into existence against very long odds. And just as your own existence seems, from a physical point of view, to have been wildly unlikely, the existence of the entire human species appears to have been a matter of blind luck.

Stephen Jay Gould argued in that the detailed course of evolution is as chancey as the path of a single sperm cell to an egg. Evolutionary processes do not innately tend toward Homo sapiens , or even mammals. Rerun the course of history with only a slight variation and the biological outcome might have been radically different.

It can be emotionally difficult to absorb the radical contingency of humanity. Nicolaus Copernicus upended this picture in the 16th century by relocating the Earth to a slightly off-centre position, and every subsequent advance in our knowledge of cosmic geography has bolstered this view — that the Earth holds no special position in the grand scheme of things. Scientific cosmology has consigned that notion to the dustbin of history. So far, so good, right?

As tough as it is to swallow, you can feel secure in the knowledge that you are an accident and that humanity is, too. But what about the universe itself? Can it be mere chance that there are galaxies at all, or that the nuclear reactions inside stars eventually produce the chemical building blocks of life from hydrogen and helium? According to some theories, the processes behind these phenomena depend on finely calibrated initial conditions or unlikely coincidences involving the constants of nature. One could always write them off to fortuitous accident, but many cosmologists have found that unsatisfying, and have tried to find physical mechanisms that could produce life under a wide range of circumstances.

Ever since the s when Edwin Hubble discovered that all visible galaxies are receding from one another, cosmologists have embraced a general theory of the history of the visible universe. In this view, the visible universe originated from an unimaginably compact and hot state. Prior to , the standard Big Bang models had the universe expanding in size and cooling at a steady pace from the beginning of time until now. These models were adjusted to fit observed data by selecting initial conditions, but some began to worry about how precise and special those initial conditions had to be.

For example, Big Bang models attribute an energy density — the amount of energy per cubic centimetre — to the initial state of the cosmos, as well as an initial rate of expansion of space itself. The subsequent evolution of the universe depends sensitively on the relation between this energy density and the rate of expansion. Pack the energy too densely and the universe will eventually recontract into a big crunch; spread it out too thin and the universe will expand forever, with the matter diluting so rapidly that stars and galaxies cannot form.

Between these two extremes lies a highly specialised history in which the universe never recontracts and the rate of expansion eventually slows to zero. Cosmological observation reveals that the value of W for the visible universe at present is quite near to 1.

Ghostly beams

If the marble happens to be exactly at the top it will stay there, but if it is displaced even slightly from the very top it will rapidly roll faster and faster away from that special state. This is an example of cosmological fine-tuning. In order for the standard Big Bang model to yield a universe even vaguely like ours now, this particular initial condition had to be just right at the beginning. Some cosmologists balked at this idea. It might have been just luck that the Solar system formed and life evolved on Earth, but it seemed unacceptable for it to be just luck that the whole observable universe should have started so near the critical energy density required for there to be cosmic structure at all.

The strange thing about this radiation is that it is quite uniform in temperature, no matter where you measure it. One might suspect that this uniformity is due to a common history, and that the different regions must have arisen from the same source. The radiation traces back to completely disconnected parts of the initial state of the universe. The uniformity of temperature would therefore already have had to exist in the initial state of the Big Bang and, while this initial condition was certainly possible, many cosmologists feel this would be highly implausible.

I n , the American cosmologist Alan Guth proposed a different scenario for the early universe, one that ameliorated the need for special initial conditions in accounting for the uniformity of background radiation and the energy density of the universe we see around us today. At first glance, the inflationary scenario seems to solve the fine-tuning problem: by altering our story about how the universe evolved, we can make the present state less sensitive to precise initial conditions. Early attempts to devise such a mechanism were inspired by the realisation that certain sorts of field — in particular, the hypothesised Higgs field — would naturally produce inflation.

But more exact calculations showed that the sort of inflation that would arise from this Higgs field would not produce the universe we see around us today. Had the constants of nature taken slightly different values, we would not be here. Unfortunately, the phenomena to be explained, which include not just the present energy density and background radiation but also the formation and clustering of galaxies and stars, require that the inflation take a rather particular form.

The constraints are so severe that some cosmologists fear one form of fine-tuning exact initial conditions in the original Big Bang theory has just been traded for another form the precise details of the inflaton field. But the inflationary scenario fits so well with the precise temperature fluctuations of the background radiation that an inflationary epoch is now an accepted feature of the Big Bang theory.

Inflation itself seems here to stay, even while the precise mechanism for inflation remains obscure, and worryingly fine-tuned. Here we reach the edge of our understanding, and a deep, correlative uncertainty about whether there is a problem with our current explanations of the universe. As we have seen, the phenomena themselves do not wear such a designation on their sleeves. These include the masses of the fundamental particles quarks, electrons, neutrinos, etc as well as physical parameters such as the fine-structure constant that reflect the relative strength of different forces.

For example, the proton is slightly lighter than the neutron because the down quark is slightly heavier than the up, and since the proton is lighter than the neutron, a proton cannot decay into a neutron and a positron. Indeed, despite intensive experimental efforts, proton decay has never been observed at all. But if the proton were sufficiently heavier than the neutron, protons would be unstable, and all of chemistry as we know it would be radically changed.

Similarly, it has been argued that if the fine-structure constant, which characterises the strength of the electromagnetic interaction, differed by only 4 per cent, then carbon would not be produced by stellar fusion. Without a sufficient abundance of carbon, carbon-based life forms could not exist.

New findings have physicists questioning reality

This is yet another way that life as we know it could appear to be radically contingent. The details of these sorts of calculations should be taken with a grain of salt. No one could sit down and rigorously work out an entirely new physics in a weekend.


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And even granting the main conclusion, that many of the most widespread structures of the universe and many of the more detailed physical structures that support living things depend sensitively on the values of these constants — what follows?