A Cosmic Photon May Be Challenging Einstein’s Physics

Welcome to Bedtime Astronomy. Explore the wonders of the cosmos with our soothing Bedtime Astronomy podcast. Each episode offers a gentle journey through the stars, planets, and beyond, perfect for unwinding after a long day. Let's travel through the mysteries of the universe as you drift off into a peaceful slumber under the night sky.

You know, usually when something travels 2 billion light years across the universe... We expect it to obey the fundamental speed limits and, you know, the standard traffic laws of physics.

Right. You definitely think so.

But back in October 2022, something hit Earth that completely broke Albert Einstein's rules. So you are about to hear the story of a particle that, well, by all known mathematical models of the universe, it just should have been annihilated long before it ever reached our solar system.

It really is such a remarkable anomaly. We're talking about a single elementary particle of light that survived an absolutely impossible journey. Yeah. And it's now forcing astrophysicists to reconsider the structural rules of spacetime itself.

Which is wild.

It is.

Yeah.

Because the data we gathered from this event, it points to mechanisms we have theorized about for decades, but we've never actually observed them in nature before.

Wow.

OK, let's unpack this by grounding it in what actually happened on October 9th, 2022. So Earth was washed over by this massive shower of photons. From a cataclysmic explosion two billion light years away.

Right. A massive burst.

And astronomers cataloged it as GRB 21009A. But it quickly earned a much more descriptive nickname, the BOAT, which stands for the brightest of all time.

Yes, the BOAT did. And, you know, gamma ray bursts are already the most energetic explosions we know of. They're typically triggered when massive stars exhaust their nuclear fuel and just, well, collapse into black holes.

Firing out those concentrated jets of pure energy.

Exactly. But the boat, it was an outlier even among Gannery bursts. The sheer volume of photons it dumped on our solar system physically saturated our satellite detectors.

Like they couldn't even process it all. Right.

The instruments were essentially blinded by the glare. It was that intense.

Okay, but it wasn't the sheer volume that caused astrophysics departments around the world to panic, right? I mean, out of that massive deluge, there was one specific photon recorded by a facility in the Russian Caucasus called the Buxan Observatory.

Yes, down on the ground.

Right, their carpet cosmic ray detector caught a single photon carrying an astonishing 300 tera electron volts, or TV, of energy.

Yeah, and to give that number some weight for anyone familiar with particle physics... 300 TeV is exponentially higher than anything we can produce artificially.

Like here on Earth? Right.

I mean, the Large Hadron Collider in Switzerland, which is the most powerful machine humanity has ever built, it maxes out at collision energies around 13.6 TeV.

Wow.

And this was 300? Yes.

This was a single massless particle of light carrying 300 TeV. It is just a staggering concentration of energy.

Okay. So we have this 300 TeV photon, and it arrived on Earth. So the objective today is to figure out the physics behind why its survival is considered impossible and how the mechanism that allowed it to survive points to a potential crack in the theory of relativity.

Which is a huge deal.

A very huge deal. So why exactly is a 300 TeV photon considered dead on arrival under standard physics? Wait, isn't space supposed to be mostly empty vacuum? Why is this photon acting like it's navigating a crowded room?

Well, that is a really common misconception. And to understand the impossibility here, we have to completely discard the idea of an empty vacuum.

Okay, so space isn't empty.

No, not at all. Intergalactic space is actually permeated by the cosmic microwave background or the CMB.

Which is the leftover stuff from the Big Bang, right?

Exactly. It's the relic radiation from the Big Bang itself.

Yeah.

It is a persistent, dense bath of low-energy photons. filling every single cubic centimeter of the universe.

Every centimeter.

Wow.

So a photon traveling from the Boe has to basically wade through this ocean of ancient CMB photons for 2 billion years.

Yes, an incredibly long swim.

But why does that matter? I mean, photons of visible light from distant galaxies cross that ocean all the time and hit our telescopes without any issue.

They do, but the rules change drastically at ultra-high energies. See, when a standard visible light photon encounters a CMB photon, nothing happens.

They just ignore each other.

Right.

They pass right through each other without interacting. But when a photon energy crosses into that extreme care electron volt range, the cross-section for interaction fundamentally shifts.

Meaning they notice each other?

Very violently, yes. A 300 TV photon colliding with a low-energy CMB photon has enough combined energy to trigger a process called pair production.

Care production, meaning... The kinetic energy of the collision is like physically converted into mass. Yes.

Matter and antimatter specifically.

Okay.

Under Einstein's mass energy equivalence, you know, E equals MC squared, the immense energy of that 300 TV photon and the CMB photon interact and spontaneously transform into an electron and a positron.

Oh, wow.

So the original light particle is just gone.

Exactly. The original 300 KV photon ceases to exist. its energy is entirely consumed in the creation of those two new particles, which then just veer off in different directions along magnetic field lines.

Okay, let me make sure I'm visualizing this correctly. A 300 TV photon traveling through the CMB is basically an arrow flying through an incredibly dense forest.

That's a good way to picture it.

But it's not just trying to avoid hitting a solid tree. If it even grazes a leaf, The fundamental physical laws of the universe force the arrow to instantaneously turn into two entirely different objects. Say, two birds that just fly away and the arrow just vanishes completely.

Yes. That framing captures the unavoidable nature of the mechanism perfectly. I mean, the mathematical probability of a 300 TV photon traveling 2 billion light years without triggering pair production is essentially zero.

Zero. Because there are just too many leaves in the forest.

Exactly. The distance is simply too immense, and the density of the CMB is too high. The photon should have been absorbed by the universe long before it reached the Milky Way.

But the Boksan Observatory has the data. The carpet detector caught it. So if we rule out a broken detector, we have to figure out how it bypassed this unavoidable annihilation.

We do.

And from what I understand, the initial attempt to solve this relied on a theoretical framework involving something called axion-like particles, or ALPs.

Yes, ALPs. And they are hypothetical ultralight particles that are often proposed as candidates for dark matter.

Okay, dark matter, right.

Yeah, but the fascinating part of ALP theory for our photon is that it allows for a temporary state change. The theory proposes that when a high-energy photon passes through a sufficiently strong intergalactic magnetic field, it can actually spontaneously oscillate into an axion-like particle.

Wait, how does a photon just change its state? I mean, it's a particle of light. It doesn't have a choice in the matter.

Well, it doesn't make a choice, right?

Yeah.

It reacts purely to environmental forces. The oscillation is driven by the interaction between the photon's electromagnetic properties and the external magnetic field.

Okay.

So the stronger the field, the higher the probability the photon alters its fundamental state.

It sounds like light passing through a specialized prism or... Maybe even like water vapor, like if the conditions, you know, the temperature and pressure in the atmosphere are just right. Invisible vapor condenses into a physical raindrop.

That's actually a great analogy.

And then when the atmospheric conditions change again, it evaporates back into invisible vapor.

The phase change analogy works very well here. Under the influence of those intergalactic magnetic fields, the photon essentially condenses into an ALP. And now the crucial detail is that ALPs do not interact with the cosmic microwave background.

Oh, because they aren't photons anymore, so the rule doesn't apply to them.

Exactly. They are completely immune to pair production.

So it tends like a fugitive putting on a disguise to sneak past a massive line of security checkpoints. They can coast right through the CMB ocean without turning into an electron and a positron.

Yes, they just slip right past the guards. And then as the ALP approaches the Milky Way... It encounters our galaxy's own localized magnetic field.

Which takes the disguise off.

Right.

It triggers the reverse oscillation. The ALP converts back into a high-energy photon just in time to hit the Earth's atmosphere and register on the carpet detector.

I mean, it's an incredibly elegant workaround for the universe. But since astrophysicists were still scratching their heads over this specific photon, I'm assuming this phase change doesn't actually solve the problem for the Biot.

Unfortunately, no. It solves the problem for photons carrying a few tens of tera-electron volts. The required magnetic field strengths and particle masses, they balance out perfectly for those lower energies.

But not for our 300 TV photon.

Right. 300 TV is simply too energetic. To force a photon of that massive magnitude to oscillate into an ALP and stay in that form long enough to cross 2 billion light years, you would need intergalactic magnetic fields installed. Far stronger than anything that actually exists in the universe.

Ah, I see.

The math just falls apart completely.

So the disguise doesn't fit.

It really doesn't.

If the environment can't force the water vapor to become a rain drought, we are basically back to square one. The photon remained a 300 TV photon, meaning it had to face the CMB ocean, meaning it should have been destroyed by pair production. Unless, of course, the rules of pair production themselves are flawed.

And this is the exact realization... that led Giorgio Galanti from the National Institute for Astrophysics and Marco Roncadeli from the National Institute for Nuclear Physics in Italy to propose a radical new model. Okay, now we're getting to the new science.

Right. They published a study in Physical Review Letters that combined the ALP theory with a violation of one of physics' most sacred principles, which is Lorentz invariance.

Okay, let's break that down because Lorentz invariance is heavy stuff. If I recall correctly from basic physics, it's a foundational pillar of Albert Einstein's special relativity.

Yes, it is.

It basically says the laws of physics, including the speed of light and how events unfold in space time, they remain identical for all observers, regardless of their constant velocity or orientation in space.

That is the core of it, yes. Lorentz invariance is the fundamental symmetry of nature. It is what keeps the universe predictable.

Okay.

But certain advanced models of quantum gravity have suggested for years that at absolute extreme energy scales, you know, approaching what we call the Planck energy, spacetime might not be the smooth, continuous fabric that Einstein described.

What would it be instead?

It might be quantized, or what physicists call foamy. Foamy spacetime? Okay, if spacetime is foamy at those extremes, Lorentz invariance might warp. But how does warping spacetime actually stop our 300 TV photon from colliding with the CMB photon and turning into an electron-positron pair?

It shifts the energetic threshold required for pair production to actually occur.

Oh, I see.

Under standard Lorentz invariance, a 300 TV photon hitting a CMB photon always meets the kinetic energy requirement to create that electron and positron. It's a guarantee.

Right.

But if Lorentz invariance is violated at extreme energies... due to the foamy structure of spacetime, the mathematics governing that interaction fundamentally altered.

So the goalposts move.

Exactly, the goalposts move. The threshold for pair production gets pushed much higher. So the 300 TD photon no longer has the necessary correct energy to trigger the creation of matter and antimatter when it hits the CMB.

Wow.

Because it can no longer interact under these bent rules, the universe effectively becomes transparent to it. It slips through untouched. And researchers describe this altered state of spacetime as, as providing a fast lane for the ultra-high energy photon.

Okay, so they merged the ALP phase change theory with this Lorentz invariance violation to explain how it survived. But hold on, I need to push back on something here.

Sure.

You just called it a fast lane where the universe becomes transparent. But I also know that this specific 300 TV photon arrived at Earth about an hour later than the rest of the gamma ray burst.

That's right, it did.

If it is in a fast lane, why is it late? That sounds like a massive detour, not a fast lane.

That is an excellent catch. And the term fast lane can definitely be misleading if we only think about velocity.

Right.

When physicists use that phrase in this context, they mean an unobstructed survival path, a lane where you don't crash into the CMB.

Yeah.

But mathematically, navigating that survival path does exact a toll on the particle's travel time.

Because of the phase change into the ALP.

Partly, yes. Remember, the Galantian-Rochedelli model is a combination of both theories. So the photon is oscillating into an axion-like particle in the presence of magnetic fields. And while standard photons are completely massless and travel at exactly the speed of light, ALPs theoretically have a microscoping amount of mass.

Right. Okay. And anything with mass, even a tiny fractional amount, cannot travel at the speed of light. It has to travel slightly slower.

Precisely. And if you combine that microscopic mass with the violation of Lorentz invariance, where the very structure of phony spacetime alters how high-energy particles propagate, you get a cumulative drag effect over a distance of 2 billion light-years.

It adds up over time.

Exactly. And the true genius of Galantine-Roccadelli's combined mathematical model is that it didn't just retroactively explain the photon's survival. It made a strict forward prediction about this drag.

Oh, really?

Yes.

It calculated that if this dual mechanism occurred— The 300 TV photon should have been delayed by roughly one hour compared to the standard low-energy photons from the exact same burst.

Here's where it gets really interesting. Because we actually have observational data to back that up, right? The Large High-Altitude Air Shower Observatory in China, LAASO, they were monitoring the boat burst as well.

They were, yes. LAASO detected the initial massive deluge of lower-energy photons. And those photons didn't need to change into ALPs or rely on relativity violations because they weren't energetic enough to trigger pair production anyway.

They just flew right under the radar.

Exactly. They sailed through the CMB, normally at speed of light, and they arrived in a massive synchronized wave. Then the researchers checked the timestamps across different observatories. Roughly one hour after that primary wave hit LA Aso, the carpet detector at Baxan registered the 300 TVO photons.

The exact delay predicted by the model. Yes.

The alignment of the observational data with the theoretical prediction is what makes this so incredibly compelling. We're looking at one elegant framework that solves two distinct anomalies simultaneously. It explains the evasion of pair production and it nails the specific one-hour delay.

That is just mind-blowing. But I do have to ask, with all this talk of Lorentz invariance being violated, does this mean Einstein was just flat-out wrong? Do we have to throw out relativity?

What's fascinating here is that We definitely aren't throwing out Einstein.

Okay, good to know.

Relativity is still the most robust framework we have for macrophysics. It still dictates the orbit of planets, the expansion of the cosmos, and, you know, the synchronization of our GPS satellites.

So it still works for the big stuff.

Exactly.

Right.

What Galanti and Roccadelli are proposing is that relativity is an incomplete picture at the absolute extreme edges of quantum mechanics. It's basically a localized exception that only activates under unimaginable energy conditions.

An asterisk on relativity, not an eraser.

That is a perfect way to put it, yes.

An asterisk. So what does this all mean for you and me? I mean, for anyone listening, why does an hour-late photon from a distant explosion matter to our understanding of reality?

Well, it matters because of the profound limitations we face in studying quantum gravity. To experimentally test theories about how spacetime behaves at these extreme subatomic levels... We would need particle accelerators capable of generating energies we can barely fathom.

Way bigger than the one in Switzerland.

Oh, massively bigger. A machine that powerful would likely need to be larger than the Earth itself. We simply cannot build it.

But we don't have to build it if the universe is running the experiment for us.

That is the crucial takeaway. The cosmos is a natural, unbridled laboratory. By observing cataclysmic events like the bow out, We are granted access to energy scales that test the extreme limits of our physical laws.

We just have to be watching at the right time.

Exactly. We are watching the universe stress test itself. Every time a particle like this arrives, it delivers data from a realm of physics we could never access on our own.

It really is profound. I mean, we started with a particle traveling through a dense cosmic ocean for 2 billion years. It bypassed the annihilation of pair production by relying on a spontaneous phase change. navigated a warped immersion of space-time that shifted the goalposts of relativity, and then arrived exactly one hour late to prove the math right.

It's quite a resume for one particle.

It really is. It shows us that the universe is far stranger, and the laws of physics are far more flexible than we ever assumed.

It reinforces the reality that our understanding of the universe is still evolving. When we push physical laws to their absolute boundaries, they reveal intricate layers of mechanics we have yet to fully comprehend.

It leaves me with one final thought to mull over long after this discussion ends. If a single burst of extreme energy from billions of years ago can briefly warp the fundamental rules of spacetime and shift the thresholds of physical reality just to ensure its own survival, what other seemingly absolute laws of the universe might temporarily bend when pushed to their absolute limits? And the really wild question, if we ever fully map these extreme exceptions to the rules, could humanity one day learn to harness those loopholes for ourselves?

A Cosmic Photon May Be Challenging Einstein’s Physics

Kapitelklicken springt direkt hin

Shownotes

Transkriptvom Podcast bereitgestellt · Zeitmarken springen hin