Technologies

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

Today’s NYT Strands Hints, Answers and Help for Jan. 9 #677

Here are hints and answers for the NYT Strands puzzle for Jan. 9, No. 677.

Looking for the most recent Strands answer? Click here for our daily Strands hints, as well as our daily answers and hints for The New York Times Mini Crossword, Wordle, Connections and Connections: Sports Edition puzzles.

Today’s NYT Strands puzzle is a fun topic — but one of the answers describes something I’ve never heard of before. Also, some of the answers are difficult to unscramble, so if you need hints and answers, read on.

I go into depth about the rules for Strands in this story.

If you’re looking for today’s Wordle, Connections and Mini Crossword answers, you can visit CNET’s NYT puzzle hints page.

Read more: NYT Connections Turns 1: These Are the 5 Toughest Puzzles So Far

Hint for today’s Strands puzzle

Today’s Strands theme is: For cubs fans.

If that doesn’t help you, here’s a clue: Like Gentle Ben.

Clue words to unlock in-game hints

Your goal is to find hidden words that fit the puzzle’s theme. If you’re stuck, find any words you can. Every time you find three words of four letters or more, Strands will reveal one of the theme words. These are the words I used to get those hints but any words of four or more letters that you find will work:

LAIR, RAIL, CROP, LAID, BALD, DEAN, BROW, DIZZY

Answers for today’s Strands puzzle

These are the answers that tie into the theme. The goal of the puzzle is to find them all, including the spangram, a theme word that reaches from one side of the puzzle to the other. When you have all of them (I originally thought there were always eight but learned that the number can vary), every letter on the board will be used. Here are the nonspangram answers:

BLACK, BROWN, GRIZZLY, PANDA, POLAR, SPECTACLED (That last one is the one I’ve never heard of! But it’s real!)

Today’s Strands spangram

Today’s Strands spangram is BEARSINMIND. To find it, start with the B that’s five rows to the right and three letters down, then wind up, over and down the whole far-right row.

Don’t miss any of our unbiased tech content and lab-based reviews. Add CNET as a preferred Google source.

Toughest Strands puzzles

Here are some of the Strands topics I’ve found to be the toughest.

#1: Dated slang. Maybe you didn’t even use this lingo when it was cool. Toughest word: PHAT.

#2: Thar she blows! I guess marine biologists might ace this one. Toughest word: BALEEN or RIGHT.

#3: Off the hook. Again, it helps to know a lot about sea creatures. Sorry, Charlie. Toughest word: BIGEYE or SKIPJACK.

Technologies

Today’s NYT Mini Crossword Answers for Friday, Jan. 9

Here are the answers for The New York Times Mini Crossword for Jan. 9.

Looking for the most recent Mini Crossword answer? Click here for today’s Mini Crossword hints, as well as our daily answers and hints for The New York Times Wordle, Strands, Connections and Connections: Sports Edition puzzles.

Need some help with today’s Mini Crossword? The Across clues were kind of tough today. Read on for all the answers. And if you could use some hints and guidance for daily solving, check out our Mini Crossword tips.

If you’re looking for today’s Wordle, Connections, Connections: Sports Edition and Strands answers, you can visit CNET’s NYT puzzle hints page.

Read more: Tips and Tricks for Solving The New York Times Mini Crossword

Let’s get to those Mini Crossword clues and answers.

Mini across clues and answers

1A clue: Question in a late-night text
Answer: YOUUP

6A clue: Plentiful
Answer: AMPLE

7A clue: Saint ___ and Nevis (Caribbean nation)
Answer: KITTS

8A clue: Baby-bringing bird
Answer: STORK

9A clue: Take care of the tab
Answer: PAY

Mini down clues and answers

1D clue: Himalayan herbivores
Answer: YAKS

2D clue: Fail to include
Answer: OMIT

3D clue: «High five!»
Answer: UPTOP

4D clue: The «U» of UV rays
Answer: ULTRA

5D clue: Annoying to deal with
Answer: PESKY

Don’t miss any of our unbiased tech content and lab-based reviews. Add CNET as a preferred Google source.

Technologies

I Got Up Close and Personal With Boston Dynamics’ New Atlas Robot

Before Atlas takes its first steps into the world of work later this year, I found myself face-to-face with CES 2026’s most talked-about robot on the show floor.

When I say that I went hands-on with the new Boston Dynamics Atlas robot, I mean that I actually held hands with it. This humanoid robot, which CNET just awarded the Best Robot of CES Award, is one of the most advanced in the world, and I couldn’t pass up the opportunity to get up close and personal with it.

This product version of the robot, which is set to be shipped to Hyundai factories imminently to start working, has been the talk of CES this year. The specific Atlas robot I encountered was a static model that wasn’t turned on or fully operational. Our interactions were, therefore, sadly one-sided. Still, I ran my hands over its soft-touch plastic shell and gently prodded at its finger joints, wondering how it would feel if they gripped me back.

People tend to have varying feelings about humanoid robots — understandable given that they are built to some degree in our image, while also usually being stronger than us, with «brains» that we don’t fully understand. Atlas definitely evokes contradictory emotions for me — even more so when I stood face-to-face with it.

I’m in awe of the engineering, a little fearful of its capabilities, hesitant about what it could mean for the future of humanity and charmed by its design and styling. The periwinkle blue iteration of Atlas that I met on the show floor at CES 2026 almost bears more resemblance to a Dyson product than it does the industrial robots that defined Boston Dynamics’ early days, when it was best known for its work with DARPA.

«There’s a lot of really specific things about this robot that probably look a little weird,» said Zachary Jackowski, Boston Dynamics VP and general manager of Atlas. He pointed to the legs, which he described as «like nothing anyone else was doing.»

Atlas’ thighs are narrow set and in line with the torso, while the calves are wider set, attached to their upper counterparts with a circular joint. This robot is, in fact, all subtle curves and soft lines. There are no harsh edges or stark angles.

During a year when CES has been flooded with humanoid robots, Atlas definitely does stand out due to its design. It appears both less classically human and less industrial than some of its peers, while also lacking the often intimidating, featureless faces they tend to exhibit. Instead, it has two low-set cameras resembling eyes placed where you’d usually expect a mouth to be. Its face is a perfect flat circle, defined by an LED halo that gives it a somewhat Pixar lamp effect.

I asked Jackowski why Boston Dynamics decided to skew so relatively unhuman with this version of its humanoid. «Well, it’s not a human,» he said. «It projects the wrong first impression about a robot to have it pretend to be something that it’s not.»

Particularly in the early days of humanoids, he added, robots won’t have anything like human-like intelligence. People should look at it and see it for what it is — a tool for performing tasks safely and efficiently.

In fact, most of the design decisions were made to keep Atlas as simple, scalable and safe as possible, Jackowski said. I remark that there’s some irony in thinking of a humanoid robot as simple, given the complexity of the technology and development process to bring Atlas to life.

The key to making it simple, Jackowski said, is having a strong enough grasp of the technology to «accomplish the complex thing of building a humanoid robot,» but then being able to take it apart and understand that you can use fewer computers and actuators in it while achieving the same results.

And it’s essential to Boston Dynamics that Atlas is perceived as simple. After all, it’s a general-purpose humanoid, which might eventually be sent far and wide to fulfil all manner of roles. Jackowski calls it the «ultimate generalist.»

Simplicity aside, there are aspects of Atlas that Jackowski believes set it apart from other humanoids at the show. «The repairability of this robot is crazy good,» he said. «The runtime is crazy good. The strength is unlike anything.»

From working in Hyundai’s manufacturing plants, Atlas’s job trajectory is to eventually graduate to many of the same industrial environments where Boston Dynamics’ Spot robot works, before moving to bussing tables in the service industry and eventually into the home. The robot will evolve between now and then, Jackowski said. However, this could be an early glimpse of the type of humanoid that will eventually be our housemate.

That’s some way away, though, which is probably for the best. As I gaze up at Atlas, which I’d guess is around the same height as my husband, my feeling is that, however impressive Atlas is, I’m still not ready for it to move in.