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What Is Dark Matter? The Answer to Universe’s Greatest Mystery Could Be Axions

The saga of how an odd hypothetical particle became a star dark matter candidate.

Physics is permeated by conundrums, and in a sense, that’s what keeps the field going. These mind-bending puzzles foster a race toward truth. But of all the dilemmas, I’d say two of them unquestionably fall under priority A.

First off, when scientists look up at the sky, they consistently see stars and galaxies traveling farther from our planet, and from each other, in every direction. The universe kind of looks like a bubble blowing up, which is how we’ve come to know it’s expanding. But something doesn’t make sense.

Space doesn’t seem to have enough stuff floating around in it — stars, particles, planets and all else — for it to inflate so swiftly. In other words, the universe is expanding way faster than our physics says it can, and it’s even picking up speed as you read this. Which brings us to problem two.

Per experts’ best calculations, galaxies are spinning so incredibly quickly as everything zips around that we’d expect the spirals to behave like out-of-control merry-go-rounds flinging metal horses off the ride. There doesn’t seem to be enough stuff in the universe to anchor them together. Yet the Milky Way isn’t drifting apart.

So… what’s going on?

As blanket terms, physicists call «missing» stuff pushing the cosmos outward dark energy, and pieces holding galaxies together — presumably in a halo-like form — dark matter. Neither interacts with light or matter we can see, so they’re essentially invisible. Combined, dark matter and dark energy make up a whopping 95% of the universe.

Zeroing in on dark matter’s portion, the authors of a recent review, published in the journal Science Advances, write that «it may well consist of one or more types of fundamental particle … although part or all of it might consist of macroscopic lumps of some invisible form of matter, such as black holes.»

Black holes or not, dark matter is totally elusive. In an effort to decode its secrets, scientists have picked a handful of suspects out of the cosmic lineup, and one of the most wanted particles is an odd little speck called the axion.

The wide-eyed hypothesis of axions

You might’ve heard of the Standard Model, which is pretty much the holy grail, ever-strengthening handbook of particle physics. It outlines how every single particle in the universe works.

However, as the Science Advances review points out, some «particle physicists are restless and dissatisfied with the Standard Model because it has many theoretical shortcomings and leaves many pressing experimental questions unanswered.» More specifically for us, it leads right into a paradox regarding a well-established scientific concept dubbed CPT invariance. Aha, the physics puzzles continue.

Basically, CPT invariance states that the universe must be symmetrical when it comes to C (charge), P (parity) and T (time). For that reason, it’s also called CPT symmetry. If everything had the opposite charge, was left-handed instead of right-handed and traveled through time backward instead of forward, it states the universe should remain just the same.

For a long while, CPT symmetry seemed unbreakable. Then 1956 came around.

Long story short, scientists found something that violates the P part of CPT symmetry. It’s called the weak force, and it dictates things like neutrino collisions and element fusion in the sun. Everyone was shocked, confused and scared.

Nearly every foundational concept of physics relies on CPT symmetry.

About a decade later, researchers discovered the weak force violating C symmetry, too. Things were falling apart. Physicists could just hope and pray that even if P is violated… and CP is violated… maybe CPT still isn’t. Maybe weak forces just need the trio to uphold CPT symmetry. Thankfully, this theory seems correct. For some unknown reason, the weak force follows total CPT symmetry despite C and CP blips. Phew.

But here’s the issue. If weak forces violate CP symmetry, you’d expect strong forces to as well, right? Well, they don’t, and physicists don’t know why. This is called the strong CP problem — and precisely where things get interesting.

Neutrons — uncharged particles within atoms — abide by the strong force. Plus, allowing for simplification, their neutral charge means they violate T symmetry. And «if we find something that violates T symmetry, then it must also violate CP symmetry in such a way that the combination CPT is not violated,» the paper states. But… that’s weird. Neutrons don’t because of the strong CP problem.

And so the idea of the axion was born.

Years ago, physicists Roberto Peccei and Helen Quinn suggested adding a new dimension to the Standard Model. It involved a field of ultralight particles — axions — that explained the strong CP problem, thereby relaxing the conditions for neutrons. Axions appeared to fix everything so well that the duo’s idea became the «most popular solution to the strong CP problem,» the paper states. It was a miracle.

To be clear, axions are still hypothetical, but think about what just happened. Physicists added a new particle to the Standard Model, which outlines specks of the entire universe. What might that mean for everything else?

The key to dark matter?

Per the Peccei-Quinn theory, axions would be «cold,» or very slowly moving through space. And… the study researchers say «the existence of [dark matter] is inferred from its gravitational effects, and astrophysical observations suggest that it is ‘cold.'»

The paper also states, «there are experimental upper limits on how strongly [the axion] interacts with the visible matter.»

So, basically, axions that help explain the strong CP problem also seem to have theoretical properties that align with those of dark matter. Extremely well.

The European Council for Nuclear Research, better known as CERN, which runs the Large Hadron Collider and is leading the charge for antimatter studies, also underlines «one of the most suggestive properties of axions is that, in a natural way, they could be produced in huge numbers soon after the Big Bang. This population of axions would still be present today and could compose the dark matter of the universe.»

There you go. Axions are among the hottest topic in physics because they seem to explain so much. But once again, those sought-after bits are still hypothetical.

Will we ever find axions?

It’s been 40 years since scientists began hunting for axions.

Most of these searches are «mainly exploiting the action field interaction with the electromagnetic fields,» say the authors in that recent review published in Science Advances.

For instance, CERN developed the Axion Search Telescope, a machine built to find a hint of the particles produced in the sun’s core. Inside our star, there are strong electric fields that could potentially interact with axions — if they’re really there, that is.

But the quest has so far faced a few pretty big challenges. For one, «the particle mass is not theoretically predictable,» the authors write — that is, we have very little idea of what an axion might look like.

Right now, scientists are still searching for them while assuming a vastly wide range of masses. Recently, however, researchers offered evidence that the particle is likely between 40 and 180 microelectron volts. That’s unthinkably small, at about 1 billionth the mass of an electron.

«In addition,» the team writes, «the axion signal is expected to be very narrow … and extremely feeble due to very weak couplings to Standard Model particles and fields.» In essence, even if minuscule axions try their very best to signal their existence to us, we might miss them. Their cues could be so weak we’d barely notice.

Despite these hurdles, the axion search marches on. Most scientists argue that they must be out there somewhere but they seem too good to be true when it comes to fully explaining dark matter.

«Most experimental attempts assume that axions compose 100% of the dark matter halo,» the study authors emphasize, suggesting that perhaps there’s a way to «look into axion physics without relying on such an assumption.»

Though they may be the star of the show, what if axions are just one chapter of dark matter history?

Technologies

Nintendo Switch 2 vs. Switch 1: Every Detail Compared

The Nintendo Switch 2’s official specs aren’t too different, but the new console has a lot of upgrades on the original Switch.

The Nintendo Switch 2 may look like its predecessor, but there’s been a lot of changes to its features and under the hood. The new console has «10x the graphics performance» compared to the original Switch, says Nvidia, which built the custom processor powering the Switch 2.  

The Switch 2, with a release date on June 5, is priced at $450 alone or $500 in a bundle with Mario Kart World, the headliner of the console’s launch games. Here’s all the info on how to preorder the Switch 2.

Note that we’re mostly comparing the Switch 2 to the original Switch 1 released in March 2017, because looping in the Switch Lite and Switch OLED gets complicated.

Design

Broadly, the Switch 2 is a larger version of its predecessor, with everything looking slightly inflated: bigger footprint, bigger screen, bigger Joy-Cons. 

Original Switch: The original Switch, with Joy-Cons slotted into the side rails, is a little over 9.4 inches wide, 4 inches tall, a little over half an inch thick and weighs about 10.5 ounces (297 grams). The Joy-Cons slide into place from the top of the device’s sides, while a thin wedge of plastic pops out of the back of the console to serve as a kickstand.

The Switch also came with a dock, which the console could slot into to for recharging and outputting to a TV or large display via HDMI port.  

Switch 2: The new Switch 2 is bigger in every way, but it has the same overall shape and layout as the original. The new Joy-Cons will indeed be held in place on the console magnetically, and connect to the console via pins. The new console also sports a wide U-shaped kickstand that spans almost its entire rear width, which can be moved around to prop up the Switch 2 at a variety of angles. Nintendo says the console has more powerful speakers, which we’re looking forward to testing.

The Switch 2’s dock is largely similar in function though it has rounded edges and an internal fan to cool down the console during long game sessions. More importantly, it can output games in 4K to TVs, but only for select games. 

Joy-Cons

The Joy-Cons were a marvel when they arrived on the first Switch, and while they’re functionally similar in its successor, there have been upgrades in the Switch 2’s controllers.

Original Switch: The Switch Joy-Cons are simple but powerful controllers that slid on and off the console via plastic rails, connecting and recharging via pins on the side. Detach and they become their own micro-controllers, with little shoulder buttons to boot.

Switch 2: The new console’s Joy-Cons are larger to fit the Switch 2, and lock into the side of the console via powerful magnets — there are small inward-facing buttons to the side of ZR and ZL to detach the controllers from the console. The larger-size Joy-Cons have longer L and R outside shoulder buttons, as well as much wider SL and SR internal shoulder buttons, which are accessible when detached from the console. 

And yes, you can use the Switch 2 Joy-Cons as mice by placing their inner edges flat on a surface. During the Nintendo Direct, we saw it being used to control active action games like the wheelchair basketball-simulating DragXDrive and strategy games like Civilization VII. 

Display size

Original Switch: The original Switch has a 6.2-inch LCD screen with 1,280×720-pixel resolution, which was reasonably impressive at launch in 2017 but has been outclassed by newer handhelds with sharper displays. The Switch OLED upgraded this with a larger 7-inch display showing deeper blacks and colors, but no upgrade in resolution. The Switch Lite has a 5.5-inch LCD screen.

Switch 2: Unsurprisingly, the Switch 2’s larger size means a larger display. The new console has a 7.9-inch 1080p LCD screen that can get up to 120Hz refresh rate in handheld mode, or up to 4K when docked and outputting to a TV. 

Why no OLED display? Possibly to save on costs… or possibly to give Nintendo room to release a Switch 2 OLED version down the line.

CPU/GPU

Original Switch: The original Switch runs on an Nvidia custom Tegra X1 processor split into four ARM Cortex A57 CPU cores, and according to Hackaday, there are four extra A53 cores that aren’t used. 

Switch 2: Once again, Nintendo hasn’t released any official info on the Switch 2’s specs, even after the Nintendo Direct reveal stream — and they most the company reveals is that it has a «custom processor made by Nvidia» on the Switch 2’s official specs page. Nvidia confirmed it also has a custom GPU, claiming that the new console has «10x the graphics performance» of the Switch 1, and the custom processor’s AI-powered features include Deep Learning Super Sampling (DLSS), face tracking and background removal for video chat and real-time ray tracing.

We do still have more supposed details from previous leaks. Months ago on X (formerly Twitter), leaker Zuby_Tech posted that the Switch 2’s CPU will be an eight-core Arm Cortex A78C. They also suggested that the GPU will be an Nvidia T239 Ampere, aligning with years of similar rumors reported on by Eurogamer and others about the custom chip, which derives from Nvidia’s Tegra line of chips for smartphones and mobile devices.

RAM and storage

Original Switch. The Switch has 4GB of LPDDR4 RAM and 32GB of onboard storage, expandable up to 2TB via microSD cards in the slot beneath the kickstand.

Switch 2: Even after the reveal stream, Nintendo didn’t release official specs for RAM. Leaker Zuby_Tech posted on X back in September suggesting the Switch 2 will have 12GB of LPDDR5 RAM and 256GB of onboard storage. That leak also suggested the new console will have two internal fans, up from the single one in the original Switch. 

Nintendo did confirm that the new console will have 256GB of onboard storage, which can be expanded with special microSD Express cards — sorry, your old Switch-compatible microSD cards won’t work on the Switch 2.

Battery life

Original Switch: The original Switch packs a 4,310-mAh battery, which gives between 4.5 and 9 hours of battery life depending on screen brightness and other factors.

Switch 2: Though Nintendo didn’t release details on the Switch 2’s capacity in the reveal stream, the company does list specs on its website, showing it packs a 5,220mAh battery. While that’s notably larger than the one in its predecessor, Nintendo estimates this will only get players between an estimated 2 and 6.5 hours, depending on games played.   

Ports

Original Switch: The first Switch sports a single USB-C port out the bottom, a 3.5mm headphone jack on the top and Wi-Fi 5 plus Bluetooth 4.1 connectivity. On the top is a slot at the top for Switch game cartridges as well as the microSD slot beneath the kickstand on the rear of the console.

Switch 2: The Switch 2 retains the original’s USB-C port on the bottom and 3.5mm jack on the top while adding another USB-C port topside, and now we know what it’s for: to connect with accessories like the Nintendo Switch Camera, a webcam-like camera on a stand to let you do Nintendo’s version of FaceTiming while you play games with your friends.

Nintendo hasn’t clarified the console’s connectivity options, and rumors are scarce on the subject. 

As for cartridges, Switch 2 will play some original Switch games in physical versions. The cartridge slot is to the right of the headphone jack in the above image, which is where the slot is on the original Switch. You can tell game cartridges from the two console generations apart by color: ones for the new Switch 2 are red, while older Switch 1 games are black.

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