ARE there vastly many near-duplicates of you reading vastly many near-duplicates of this article in vastly many parallel universes? Is consciousness a fundamental property of all matter? Could reality be a computer simulation? Reader, I can hear your groans from here in California.

We are inclined to reject ideas like these on the grounds that they sound preposterous. And yet some of the world’s leading scientists and philosophers advocate for them. Why? And how should you, assuming you aren’t an expert, react to these sorts of hypotheses?

When we confront fundamental questions about the nature of reality, things quickly get weird. As a philosopher specialising in metaphysics, I submit that weirdness is inevitable, and that something radically bizarre will turn out to be true.

Which isn’t to say that every odd hypothesis is created equal. On the contrary, some weird possibilities are worth taking more seriously than others. Positing Zorg the Destroyer, hidden at the galactic core and pulling on protons with invisible strings, would rightly be laughed away as an explanation for anything. But we can mindfully evaluate the various preposterous-seeming ideas that deserve serious consideration, even in the absence of straightforward empirical tests.

The key is to become comfortable weighing competing implausibilities, something that we can all try – so long as we don’t expect to all arrive at the same conclusions.

Let us start by clarifying that we are talking here about questions monstrously large and formidable: the foundations of reality and the basis of our understanding of those foundations. What is the underlying structure…

YOU open a door and it hits you – a flare of warmth on your skin. You brace yourself to go inside, battling smoke and heat. Flames flicker around you as you make your way through a burning building. You find what you came for and escape. Outside, it is so cold you start to shiver, while your hands and feet go numb.

But then you remove your headset and it all stops. You just finished an incredibly realistic training exercise. None of those sensations were caused by changes in your surroundings, although they felt real. Instead, chemicals carefully selected to mimic different feelings were pumped onto your skin.

Such stimulants have long been useful for understanding touch, the most complex of all human senses. In the 1990s, studies of capsaicin, an extract of chilli peppers, and menthol, found in peppermint, helped us pin down how our bodies react to hot and cold conditions. Now, Jasmine Lu and her colleagues at the University of Chicago are using this knowledge to create chemically induced sensations, to make virtual environments astonishingly realistic.

In a technology dubbed chemical haptics, they have built a wearable device that, when placed on the skin, can cause the wearer to experience a range of sensations – hot or cold, numb or tingly – on demand. Its uses could include creating intensely realistic virtual worlds for gamers to explore or for training firefighters. But will we ever be able to fully replicate the experience of touching something real, and what might we lose if we can’t?…

ONE snowy day last year, I trekked out of Vienna, Austria, winding my way to one of the city’s graveyards to visit the final resting place of a giant of 19th-century physics. Ludwig Boltzmann’s tombstone features an imposing bust of the man, frowning down with a severe expression. And there above him, in gold lettering, is his formula for entropy. It must be one of only a few tombstones in the world adorned with an equation.

I had come for a spot of contemplation because I think Boltzmann’s century-old ideas could help solve one of the trickiest problems in physics right now: how quantum particles, which exist in a fuzzy cloud of possible states, give rise to the solid, well-defined world of snow, leaves, tombstones and everything else around us.

There have been many attempts to explain this over the years, including the outlandish idea that the other quantum possibilities play out in many other parallel universes or that they simply vanish. But my colleagues and I suspect the answer could lie with Boltzmann.

The theory he worked, called thermodynamics, is centred on entropy, a measure of how disordered things are. It explains how things cool down, power up and, crucially for our purposes, mix. It covers everyday goings-on, like milk mixing into coffee. But if we are right, its powers also extend to the quantum realm. We think those quantum possibilities are never lost at all: instead, they are just mixed so thoroughly into the cracks of reality that we can’t see them. It this is…

THE standard model of particle physics is a stunning achievement. It offers a concise description of the basic constituents of the universe, the particles and forces that make reality, that agrees with every experimental test we have thrown at it. By most measures, it is the most successful scientific theory ever devised.

But as we explore in our special feature celebrating its 50th anniversary, the standard model remains unfinished. It leaves open several profound questions, from the true nature of dark matter and dark energy to why there is more matter than antimatter in the universe.

Physicists are desperately seeking …

IMAGINE you could see through everyday objects to the stuff they are made of. If you zoomed in on the arm of a chair, say, you would see that it is made of atoms. Zoom in again and you would see that those atoms contain subatomic particles called protons, neutrons and electrons. Zooming further still, you would see that the protons and neutrons are composed of quarks.

These are the layers of reality, and this is how physicists understand the universe: by breaking everything down into its constituent parts, an approach known as reductionism. As a particle physicist, I grew up on this philosophy. It has brought physics a long way – it is how we built our current picture of matter and its workings, after all. But now, with further progress stalling, I am convinced we need to go about things differently from here.

Rather than zooming ever further inwards, I think we need to zoom out. In doing so, we may see that everything there is, including such seemingly fundamental things as space and time, fragment out of a unified whole. This might sound like philosophy or mysticism, but it is in fact a direct result of applying quantum mechanics to the entire cosmos. When you do that, you realise that the universe isn’t fundamentally made of separate parts at all, but is instead a single, quantum object.

It is a radical idea, and one we are just beginning to test experimentally. But if it is correct, it could help solve some of the …

IMAGINE approaching a Renaissance sculpture in a gallery. Even from a distance, it looks impressive. But it is only as you get close and walk around it that you begin to truly appreciate its quality: the angle of the jaw, the aquiline nose, the softness of the hair rendered in marble.

In physics, as in life, it is important to view things from more than one perspective. As we have done that over the past century, we have had plenty of surprises. It started with Albert Einstein’s theory of special relativity, which showed us that lengths of space and durations of time vary depending on who is looking. It also painted a wholly unexpected picture of the shared reality underneath – one in which space and time were melded together in a four-dimensional union known as space-time.

When quantum theory arrived a few years later, things got even weirder. It seemed to show that by measuring things, we play a part in determining their properties. But in the quantum world, unlike with relativity, there has never been a way to reconcile different perspectives and glimpse the objective reality beneath. A century later, many physicists question whether a single objective reality, shared by all observers, exists at all.

Now, two emerging sets of ideas are changing this story. For the first time, we can jump from one quantum perspective to another. This is already helping us solve tricky practical problems with high-speed communications. It also sheds light on whether any shared reality exists at the quantum level. Intriguingly, the answer seems to be no – until we start talking to each other. …

A mechanical backpack can enhance the sensation of jumping or falling in virtual reality by sliding a weight up or down.

Simulating forces on the body while in virtual reality (VR), like those you might feel in a roller coaster or a racing car, often requires bulky and expensive hardware that is unsuitable for home use.

Instead, Pedro Lopes at the University of Chicago and his colleagues have developed a backpack, called JumpMod, that can create the sensation of being pulled up or down by modifying the user’s sense of vertical momentum. “You can play lots of tricks just by playing with perception, rather than physically having these massive infrastructures,” says Lopes.

To trick the brain, JumpMod senses within milliseconds the need to give a sense of jumping or falling and then quickly moves a 2-kilogram weight up or down to achieve this.

Lopes and his colleagues used the device to create a variety of effects in a VR simulation. In one part of the game, players collected a token that enabled them to jump higher, helping them to leap over a cow. By moving the weight up as the player was lifting off the ground, JumpMod made it feel as if they were jumping higher.

In another scenario, players had to smash a pumpkin by jumping on it. By moving the weight down as the player was descending, JumpMod made it feel as if they were landing harder.

At the end of the game, the player is lifted off the ground by a bird. The weight in the backpack moved downwards to give a sense of being lifted upwards.

Lopes presented the work at the Conference on Human Factors in Computing Systems in Hamburg, Germany, on 24 April. He says the system could also be used for training people to jump more effectively through physical feedback.

It is a novel VR accessory, but it would be good to see longer-term data on its use to rule out the effect of novelty in the initial studies, says Brendan Walker at the University of Middlesex in London. It could also be more ergonomically designed to avoid putting all of the force through the rucksack straps, he says.

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Rats can move objects in virtual reality just by thinking of where they want them to go, thanks to an artificial intelligence that reads their intentions in the brain.

A mental map of our local surroundings is stored in a brain region called the hippocampus, which contains neurons called “place cells”. These cells fire different patterns of electrical impulses depending on where you are.

However, it has been unclear whether this activity in the hippocampus can be consciously controlled by imagining …

A face mask designed to enhance virtual reality can release various smells to make the simulation more immersive. It could even be used to mimic the odour of absent loved ones during virtual meetings, say its creators.

The senses of sight, sound and touch are all commonly catered for by virtual reality systems, but smell isn’t usually despite its important role in day-to-day life and in forming and recalling memories.

Xinge Yu at City University of Hong Kong says earlier smell generators were large, “clumsy” devices, which leaked odour throughout a large area and were sluggish to switch from scent to scent.

His team has created two devices that can release odours on demand. One is a flexible patch around 5 centimetres long mounted on the upper lip containing two cells, each with the ability to release one scent. The other is a face mask with a grid of nine different smells, which can also be combined to create other odours.

Each device is controlled by a small chip that communicates with computers wirelessly via Bluetooth to coordinate the release of smells as the wearer nears an odorous object in VR.

The smells are created by liquid perfumes added to containers of paraffin. When a smell is needed, the cell is heated to 50°C (122°F) with a small radiator. Because both devices are close to the nose, wearers can detect the scents within 1.5 seconds of them being switched on.

In an experiment with the face mask, 11 volunteers were able to detect different odours, including mint, jasmine, lavender and pineapple, with an average success rate of 93 per cent.

Yu says the system can make virtual reality more convincing, but could also be used to make people in different places feel closer to each other.

“By wearing the olfaction system, children could sense their absent families’ odour, and separate couples could feel each other by smelling their odours,” he says. “In terms of entertainment, users could experience various outdoor environments with different nature smells at home by VR. We think bad smells can be used as easily as pleasant smells.”

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