• Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
    Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.

The 2020 Year in Physics

erek

erek

8=D
2FA
Joined
Dec 19, 2005
Messages
17,755
"The biggest puzzle in cosmology right now has to do with the Hubble constant, a measure of the speed at which the universe is expanding. Data from the early universe predicts one value. Data from the modern universe predicts another. What might be causing the discrepancy? Cosmologists have no end of ideas, but one overlooked option is the possible existence of magnetic fields at the birth of the universe. Key evidence in favor of this hypothesis emerged when astronomers discovered the largest known magnetic field in the cosmos — 10 million light-years of magnetized space permeating the voids between galaxy clusters. Where could it have come from, if not the Big Bang itself?"

1608839209919.png


https://www.quantamagazine.org/quantas-year-in-physics-2020-20201223/
 
Dark Energy is still the theory for the expanding universe exists?

I didn't know black holes eventually evaporate? I thought they'd be around forever and eventually gobble up everything.
 
RomeoGolf87 said:
Dark Energy is still the theory for the expanding universe exists?

I didn't know black holes eventually evaporate? I thought they'd be around forever and eventually gobble up everything.
Click to expand...

Scientists Claim Dark Energy does not Exist, and Accelerated Expansion of Universe is an Illusion Caused by Gravity slowing down time

Dark energy ‘doesn’t exist’: Challenging the theory of an expanding universe​

So can't be pushing 'lumpy' Universe apart.

A group of physicists and astronomers from the University of Canterbury in Christchurch, New Zealand, are now challenging the conventional wisdom by demonstrating that the Universe is expanding in a more diversified or “lumpier” way using enhanced light-curve analysis of type Ia supernovae.

According to the research team, there is no dark energy. The new discoveries support the so-called “timescape” hypothesis of cosmic expansion. Since the differential stretching of light results from our calibration of time and distance rather than from a speeding universe, dark energy is not required in this paradigm.

Time passes quicker in such empty space than in a galaxy because gravity slows time.

According to the model, a clock in the Milky Way would run roughly 35% slower than one at an average location in vast cosmic gaps, indicating that billions more years would pass in those voids. The expansion appears to accelerate because the more expansive the empty void that extends in the Universe, the more space it yields for expansion.

Professor David Wiltshire, who led the study, said: “Our findings show that we do not need dark energy to explain why the Universe appears to expand at an accelerating rate.

“Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a Universe as lumpy as the one we live in.”

He added: “The research provides compelling evidence that may resolve some of the key questions around the quirks of our expanding cosmos.
Click to expand...

“With new data, the Universe’s biggest mystery could be settled by the decade’s end.”

https://www.techexplorist.com/dark-energy-exist-challenging-theory-expanding-universe/94988/


Dark Energy may no longer be necessary to explain the 'expanding' universe. Lumpy Matter in our galaxies slows down time (& expansion of space) while the clock (& hence space) runs faster in the voids

https://cybernews.com/science/dark-energy-universe-expansion/


In 1990s Hubble telescope found evidence that Universe expansion was accelerating. So physicists introduced concept of dark energy

In a new paper, researchers from @UCNZ argue in favour of a model that does away with #DarkEnergy

https://www.yourweather.co.uk/news/...rchers-argue-model-rules-out-dark-energy.html


When first tested in 2017, the #timescape model offered a slightly better fit than the ΛCDM (#DarkEnergy) model, but with recent observations — including data from over 1,500 supernovae cataloged by the Pantheon+ collaboration — the evidence is stronger

https://www.labrujulaverde.com/en/2...illusion-caused-by-gravity-slowing-down-time/

https://apnews.com/article/dark-energy-desi-cosmology-astronomy-7856ae96fab5cb42e6b4a6fd7c3555ec

“Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a Universe as lumpy as the one we actually live in."​
​
https://www.independent.co.uk/space/dark-energy-universe-cosmos-expansion-b2669078.html
 
Last edited:
Marees said:
Scientists Claim Dark Energy does not Exist, and Accelerated Expansion of Universe is an Illusion Caused by Gravity slowing down time

Dark energy ‘doesn’t exist’: Challenging the theory of an expanding universe​

So can't be pushing 'lumpy' Universe apart.



“With new data, the Universe’s biggest mystery could be settled by the decade’s end.”

https://www.techexplorist.com/dark-energy-exist-challenging-theory-expanding-universe/94988/


Dark Energy may no longer be necessary to explain the 'expanding' universeLumpy Matter in our galaxies slows down time (& expansion of space) while the clock (& hence space) runs faster in the voids

https://cybernews.com/science/dark-energy-universe-expansion/


In 1990s Hubble telescope found evidence that Universe expansion was acceleratingSo physicists introduced concept of dark energyIn a new paper, researchers from @UCNZ argue in favour of a model that does away with #DarkEnergy

https://www.yourweather.co.uk/news/...rchers-argue-model-rules-out-dark-energy.html


When first tested in 2017, the #timescape model offered a slightly better fit than the ΛCDM (#DarkEnergy) model, but with recent observations — including data from over 1,500 supernovae cataloged by the Pantheon+ collaboration — the evidence is stronger

https://www.labrujulaverde.com/en/2...illusion-caused-by-gravity-slowing-down-time/

https://apnews.com/article/dark-energy-desi-cosmology-astronomy-7856ae96fab5cb42e6b4a6fd7c3555ec
Click to expand...

My Layman's interpretation:

  1. Universe has been expanding since Big Bang
  2. In 1998, it was observed that the expansion of the universe was accelerating
  3. To explain this 'accelerated' expansion, a new mathematical factor viz the Dark Energy (Cosmological Constant) was introduced in Einstein's equations of gravity
  4. Now a team of NZ scientists claim that this 'acceleration' of the expansion is an artifact caused by the fact that the clock runs slower in our galaxy due to mass of stars etc
  5. As a result we may not need dark energy / cosmological constant to explain the 'acceleration' in the expansion of our universe
 
Don't neutrinos have the higgs particle? Aren't neutrinos weakly interacting particles? What's the definition of dark matter again?

I am more math than physics so tend to think about definitions when it might be more appropriate to consider what we hope to explain in terms of phenomena. But physicists should be better about well defined definitions.
 
1.1.2.3.5... said:
Don't neutrinos have the higgs particle? Aren't neutrinos weakly interacting particles? What's the definition of dark matter again?

I am more math than physics so tend to think about definitions when it might be more appropriate to consider what we hope to explain in terms of phenomena. But physicists should be better about well defined definitions.
Click to expand...
There is one type of neutrino which is a candidate for dark matter. (Dark matter = matter that is missing/needed to balance equations/observations but not yet observed so far). Also other types of objects such as WIMPs & MACHOs have been proposed.

Dark Energy is a more nebulous concept but again derived from missing numbers needed to balance our equations.
Dark Energy causes expansion of space to accelerate. If dark energy is not a constant but keeps increasing then the universe could be ripped apart one day
 
Last edited:
Marees said:
There is one type of neutrino which is a candidate for dark matter. (Dark matter = matter that is missing/needed to balance equations/observations but not yet observed so far). Also other types of objects such as WIMPs & MACHOs have been proposess
Click to expand...

wikipedia, so grain of salt..
"In principle, "dark matter" means all components of the universe which are not visible but still obey ρ ∝ a−3 . In practice, the term "dark matter" is often used to mean only the non-baryonic component of dark matter, i.e., excluding "missing baryons".[51] Context will usually indicate which meaning is intended."

Seems like neutrinos meet the technical definition, if that's correct.

That said, they don't account for missing matter and so are not (according to my reading) considered dark matter.

And there's why I stepped away from physics and stuck with math comp sci and engineering. Physics (theoretical physics anyways) lacks the rigor I prefer.
 
1.1.2.3.5... said:
Seems like neutrinos meet the technical definition, if that's correct.

That said, they don't account for missing matter and so are not (according to my reading) considered dark matter.

And there's why I stepped away from physics and stuck with math comp sci and engineering. Physics (theoretical physics anyways) lacks the rigor I prefer.
Click to expand...
While the 'technical definition" may be there, the problem neutrinos have is they move too damn fast (practically the speed of light), as a result they don't clump together, which is what observations of dark matter show. Unless there happens to be the first ever "slow" neutrinos discovered.

The thing with dark matter is it isn't one thing, black holes are dark matter, white dwarfs that are far away are dark matter, it's like looking at a forest but not realizing the majority of life is actually under the ground.

That said, dark matter and dark energy aren't in any way connected, well at least on the surface. But astrophysics really isn't my jam, I don't mind teaching astronomy to others as it's known but I do get quite a bit uncomfortable whenever questions of dark matter/dark energy come up, and it's not because I'm incapable of admitting "I don't know" I'm actually very comfortable doing that, it's that students don't tend to like that as an answer, and I don't know how to make them be at peace with something we don't know.... with the always predictable question "will something we don't know be on the final?" and my quick fire smart ass response "I'm sure a lot of what you don't know will be on the final"
 
First, I'm not the one that necro'd this almost 5yr old thread. But since someone else did: lets's say I been melting faces elsewhere with some wildly crackpot physics. Instead the usual time, space, and energy, I figure one might be simpler than three. So reimagined my pet rock of timeflow only. Perpendicular loops of flow, each with it's own trafiic jam of perpendicular gravity displacing the future of another. Space also flowing, just three loops happen to flow same rate so they don't smear. It gets vastly nuttier, but news probably ain't the right place. Differs considerably from reverse engineering top down.
 
Dark Energy is back

Ask Ethan: Can a lumpy Universe explain dark energy?​

Our Universe isn’t just expanding, the expansion is accelerating. Instead of dark energy, could a “lumpy” Universe be at fault?

Key Takeaways
  • Ever since the late 1990s, supernovae have provided the most compelling evidence for the existence of dark energy: the dominant form of energy in our cosmos, causing our Universe’s expansion to accelerate.
  • Many have tried to concoct viable alternatives that do away with dark energy altogether, with one option — David Wiltshire’s Timescape cosmology — claiming it can successfully explain observations without dark energy at all.
  • Despite the popularity of such alternatives, they fail spectacularly when confronted with the full suite of evidence about the Universe. Here’s why dark energy can’t be eliminated so easily.

the Universe is not so lumpy or clumpy that our foundational assumptions about it — that it’s isotropic and homogeneous on the largest scales — should be thrown out.

https://bigthink.com/starts-with-a-bang/lumpy-explain-dark-energy/
 
Marees said:
Physicists be like: "lets imagine a spherical cow..." (otherwise the calculations become too complex to do !!)


View: https://youtube.com/watch?v=frJy-sSriHM
Click to expand...



all models are wrong, but some are useful, and whatever your misgivings about dark energy, it certainly has proved to be useful for explaining many observations, such as the features of the cosmic microwave background and the growth of galactic structures. It will take a lot more than one paper to convince astrophysicists that dark energy should be declared dead.


https://nautil.us/these-physicists-want-to-ditch-dark-energy-1177085/
 

Scientists claim to find 'first observational evidence supporting string theory,' which could finally reveal the nature of dark energy​

News
By Andrey Feldman published yesterday
Physicists have proposed a new model of space-time that may provide the 'first observational evidence supporting string theory,' a new preprint suggests.

Their calculations suggest that, at the smallest scales, space-time behaves in a profoundly quantum way, differing drastically from the smooth, continuous structure we experience in everyday life. According to their findings, the coordinates of space-time do not "commute" — meaning the order in which they appear in equations affects the outcome. This is similar to how a particle's position and velocity behave in quantum mechanics.

One of the most striking consequences of this quantum space-time, as predicted by string theory, is that it naturally leads to cosmic acceleration. Moreover, the researchers found that the rate at which this acceleration decreases over time aligns remarkably well with the latest observations from the Dark Energy Spectroscopic Instrument (DESI).

https://www.livescience.com/physics...ould-finally-reveal-the-nature-of-dark-energy



In a new paper that was posted in the preprint database arXiv but has not been peer-reviewed, physicists Sunhaeng Hur, Djordje Minic, Tatsu Takeuchi (Virginia Tech), Vishnu Jejjala (University of the Witwatersrand), and Michael Kavic applied string theory to analyze space-time at the quantum level.

By replacing the Standard Model's description of particles with the framework from string theory, the researchers found that space-time itself is inherently quantum and noncommutative, meaning the order in which coordinates appear in equations matters.

This radical departure from classical physics allowed them to derive the properties of dark energy not just from experimental data, but directly from a fundamental physical theory. Their model not only yielded a dark energy density that closely matches observational data but also correctly predicted that this energy should decrease over time, aligning with DESI's findings.

One of the most striking aspects of their result is that the value of dark energy depends on two vastly different length scales: the Planck length, the fundamental scale of quantum gravity, which is about 10⁻³³ centimeters; and the size of the universe, which is billions of light-years across. Such a connection between the smallest and largest scales in the cosmos is highly unusual in physics and suggests that dark energy is deeply tied to the quantum nature of space-time itself.
 
I think the biggest problem in cosmology is the scale outside of our universe. I believe space was not created with the big bang, but already existed. Not only that, but time as well. If there is no time or space outside of our universe, how is there time and space in a universe without relation to the outside? Because we say there's nothing outside the bubble?
 
We're in a simulation and Dark Matter is just all of the tiny nanomachine code made to keep it all together. So small that we can't even detect them, because they're the foundational unit of existence.

You heard it here folks, do I get to sell 2 million books?
 
BravO))) said:
I think the biggest problem in cosmology is the scale outside of our universe. I believe space was not created with the big bang, but already existed. Not only that, but time as well. If there is no time or space outside of our universe, how is there time and space in a universe without relation to the outside? Because we say there's nothing outside the bubble?
Click to expand...
That's the thing there is no outside, that's the whole concept of a UNIverse, it is everything. No bubble we live in, as a result there is no outside.
 
sfsuphysics said:
That's the thing there is no outside, that's the whole concept of a UNIverse, it is everything. No bubble we live in, as a result there is no outside.
Click to expand...
I understand that, which is why I stated my thoughts. Time and gravity are linked, and for a singularity to encapsulate time, ie: no time outside the universe, implies that the singularity that caused the big bang internalized gravity, which I don't agree with.
 
Marees said:
Dark Energy is back

Ask Ethan: Can a lumpy Universe explain dark energy?​

Our Universe isn’t just expanding, the expansion is accelerating. Instead of dark energy, could a “lumpy” Universe be at fault?

Key Takeaways
  • Ever since the late 1990s, supernovae have provided the most compelling evidence for the existence of dark energy: the dominant form of energy in our cosmos, causing our Universe’s expansion to accelerate.
  • Many have tried to concoct viable alternatives that do away with dark energy altogether, with one option — David Wiltshire’s Timescape cosmology — claiming it can successfully explain observations without dark energy at all.
  • Despite the popularity of such alternatives, they fail spectacularly when confronted with the full suite of evidence about the Universe. Here’s why dark energy can’t be eliminated so easily.

the Universe is not so lumpy or clumpy that our foundational assumptions about it — that it’s isotropic and homogeneous on the largest scales — should be thrown out.

https://bigthink.com/starts-with-a-bang/lumpy-explain-dark-energy/
Click to expand...

This PBS Space Time video does a good job of explaining the timescapes alternative to the dark energy model



View: https://youtube.com/watch?v=SXg6YVcdOcA
 
Neat idea, but even says near the end that its largely incomplete with with voids not having as much time flow difference to really account for it.

That said the idea of different regions of space with different time flow on large larger scales is kind of neat. Park a quantum super duper computer in a void to do more calculations, then beam the result home... of course the time to travel would negate any advantages but some neat scifi ideas floating around there.
 
RomeoGolf87 said:
Dark Energy is still the theory for the expanding universe exists?

I didn't know black holes eventually evaporate? I thought they'd be around forever and eventually gobble up everything.
Click to expand...
Dark Energy is still something that nobody knows for sure that exists. Black holes evaporate because of Hawking radiation, but again nobody can prove this. Like most things we see in the universe, it's a prediction from physics. Dark Energy is a term used to describe what could be pulling the universe apart, but we aren't exactly sure the universe is pulling itself apart. Hawking radiation is a way to maintain the black hole information paradox. Information can never be destroyed so we have Hawking radiation to maintain this theory.

View: https://youtu.be/WNyY1ZYSzoU?si=k2dJqOkfprtyjDTs
 
DukenukemX said:
Hawking radiation is a way to maintain the black hole information paradox. Information can never be destroyed so we have Hawking radiation to maintain this theory.
Click to expand...
Actually Hawking radiation was initially nothing more than a thermodynamics argument. The relationship with information paradox came considerably later if memory serves.

Ironically though, the "nobody knows" that bugs me are the axioms like the information paradox even being a paradox, or naked singularity theorems and the like.
 
sfsuphysics said:
Actually Hawking radiation was initially nothing more than a thermodynamics argument. The relationship with information paradox came considerably later if memory serves.

Ironically though, the "nobody knows" that bugs me are the axioms like the information paradox even being a paradox, or naked singularity theorems and the like.
Click to expand...
One idea I came up with is that maybe black holes may eventually blow up. How large can a black hole get and does a larger size make them unstable? If a black hole explodes then that would fix the information paradox. It would also explain the big bang or why there's dark energy. If you got one of these monsters in the universe then the universe may start pulling towards it. The other problem is how old the universe is and I think it's infinite. It has always existed but our minds can't fathom this. If the universes future is infinite then the past is infinite. Black holes maybe the universes recycling center and if and when they explode would help create new stars.


View: https://youtu.be/EIGz1EF25cY?si=fvgJi1ya7rvRG7qf
 
DukenukemX said:
One idea I came up with is that maybe black holes may eventually blow up. How large can a black hole get and does a larger size make them unstable?
Click to expand...
You would need some mechanism to have them blow up, and consider things must go FTL to escape the event horizon there's simply no known mechanism that can possibly do it. I think the closest anyone has hypothesized is that black holes connect to white holes which spew stuff out, but there's been zero evidence of that so... yeah.

DukenukemX said:
The other problem is how old the universe is and I think it's infinite. It has always existed but our minds can't fathom this. If the universes future is infinite then the past is infinite.
Click to expand...
Not exactly a new idea, and you'd be surprised how people think. In the past when I've taught general astronomy classes and go over the Big Bang, I would stress that questions like "what happened before the Big Bang?" are illogical because time started at that point as the Big Bang was a time like singularity, so "before" just does not compute. Now that is very hard for student's minds to fathom, the idea that the Universe has always been here, that's fairly easy to grasp for people, but then again if you tell them the Universe is 13.6 billion years old they'll equally go "ok".
 
DukenukemX said:
One idea I came up with is that maybe black holes may eventually blow up. How large can a black hole get and does a larger size make them unstable? If a black hole explodes then that would fix the information paradox. It would also explain the big bang or why there's dark energy. If you got one of these monsters in the universe then the universe may start pulling towards it. The other problem is how old the universe is and I think it's infinite. It has always existed but our minds can't fathom this. If the universes future is infinite then the past is infinite. Black holes maybe the universes recycling center and if and when they explode would help create new stars.


View: https://youtu.be/EIGz1EF25cY?si=fvgJi1ya7rvRG7qf
Click to expand...

I can give you my theories on what's inside a black hole (based on classical model rather than quantum gravity model)

But be warned that I got awarded with 2 Badges Of Shame & multiple negative points when I posted this in the physics forums blog

https://www.physicsforums.com/threads/is-there-a-white-hole-inside-every-black-hole.1082533/

Here is my mental model of a blackhole
  1. Collapsing matter forms event horizon of a black hole (this is known & uncontroversial)
  2. The moment an event horizon forms
    1. A white hole is formed inside the event horizon
    2. The exterior of the black hole's event horizon gets entangled to the interior of the white hole's horizon
    3. The white hole keeps bursting out (like what DukenukemX mentioned) — but it keeps getting recreated due to the Dense mass at the centre of the black hole
    4. It is like a flickering flame. The white hole bursts but new one created in its place & this process repeats ad infinitum as long as the black hole's event horizon persists
  3. This whole thing creates multiple layers / zones in the black hole
    1. Outside the black hole's event horizon, everything appears normal — you can't distinguish between classical gravity & quantum gravity here
    2. In the immediate interior of the event horizon the space is stretched like pasta strands oriented towards the centre / white hole. You can think of this as a laminar flow with all the individual pasta space strands co-existing but aligned towards the centre / white hole
    3. The next zone is a zone of turbulence where the laminar flow of space alignment is disturbed by the distortion caused by the mass continuously spewed out by the white hole
    4. The next zone just above the white hole is continuous & complete chaos, as the mass ejected by the white hole mixes with shredded tiny bits of space time
    5. The last layer / zone is the white hole at the centre — this keeps getting rejunavated continuously as stated earlier
  4. To summarize — no Hair outside black hole's event horizon but dangling / dancing hair just inside the event horizon. As you progress further interior it just becomes more & more chaotic until you finally encounter the white hole which is in a constant bursting state but this is hidden to the outside world by the black hole's event horizon
  5. Due to hawking's radiation the black hole (it's event horizon) is constantly shrinking over a period of time. Eventually the black hole gets small enough for the event horizon to disappear. Here the white hole momentarily pops into view & destructs itself in one final moment of glory
 
Last edited:
sfsuphysics said:
You would need some mechanism to have them blow up, and consider things must go FTL to escape the event horizon there's simply no known mechanism that can possibly do it. I think the closest anyone has hypothesized is that black holes connect to white holes which spew stuff out, but there's been zero evidence of that so... yeah.


Not exactly a new idea, and you'd be surprised how people think. In the past when I've taught general astronomy classes and go over the Big Bang, I would stress that questions like "what happened before the Big Bang?" are illogical because time started at that point as the Big Bang was a time like singularity, so "before" just does not compute. Now that is very hard for student's minds to fathom, the idea that the Universe has always been here, that's fairly easy to grasp for people, but then again if you tell them the Universe is 13.6 billion years old they'll equally go "ok".
Click to expand...
Just stuck me that blowing up can happen not just with a white hole but also an anti-matter

So can I say that the (neglected) backreaction effects matter within the large densities in the interior of the black hole?

Does backreaction cause spacetime to tear apart matter at the centre of a blackhole (creating anti-matter or white hole like effects) ??
 
came across this today

quantum gravity

Old ‘Ghost’ Theory of Quantum Gravity Makes a Comeback​

By Charlie Wood
November 17, 2025
Has the secret to understanding gravity been hiding in plain sight for nearly 50 years?

When physicists first invented quantum field theory and tried to use it to ask questions about electrons and photons, their calculations went infinite because each term in a sum tried to account for a never-ending continuum of ever-smaller ripples. But a sum of infinite terms was no answer at all.​
​
this trick, known as renormalization, was a way of blurring out the smallest ripples in a field and including only their net effects. In the case of the electromagnetic field, this works because the impact of the small ripples is limited; the smaller the ripples get, the less they influence the larger ripples.​
Stelle figured out that he could modify Einstein’s equation so that space-time more closely resembled the electromagnetic field, with ripples that became less significant as they got smaller. Their overall effects could then be captured in just a few measurable constants, analogous to the electron’s charge and mass in electromagnetism. This theory of gravity, which came to be known as quadratic gravity because it contained two new terms related to the square of the curvature, was renormalizable. It made just as much sense as electromagnetism.​


The problem was that this enhanced fabric of space-time could now host three types of ripples. The first term represents the normal gravitons. But the two curvature-squared terms bring two new particles into the picture. One is inoffensive, what Stelle called a “sweet little scalar” particle. But the other is a ghoul.

An unwelcome minus sign stemming from the third term unleashes chaos. The associated particle has negative energy, so the space-time fabric actually gains energy by creating it. This means that more and more of such a particle will spontaneously appear, whipping space itself into an increasingly energetic inferno.

Worse, events involving this third particle may have a negative probability of taking place — a meaningless proposition.

Shortly after Stelle published his research in 1977(opens a new tab), physicists stumbled across a healthier quantum gravity theory called supergravity. It solved a handful of problems by positing that each known elementary particle teams up with an as-yet-undiscovered “superpartner” particle. Supergravity immediately captured the attention of theoretical physicists, including Stelle. The theory would eventually merge with string theory and dominate the field for decades.​
Interest rose in the 2010s as string theory failed to deliver the spectacular breakthroughs its early practitioners had promised, and superpartners failed to materialize in experiments at the Large Hadron Collider.​

in simple scenarios, the ghost particles don’t actually wreak the havoc physicists feared. They are so unstable, they tend to vanish before they have time to fire up the vacuum or manifest negative probabilities. The vacuum stayed calm, and probabilities continued to add up to 100% — an essential property known as unitarity.

They show up only fleetingly, over short distances. In those instants there is a heavy price to be paid, but it isn’t stability or unitarity. Rather, it’s the normally rigid ordering of cause and effect. That minus sign allows ghost particles to briefly skip backward in time, where they can influence particles that they otherwise couldn’t.

In this picture, the inexorable forward flow of time that we experience would emerge as a delicate average over lots of temporally squishy micro-moments.



View: https://youtube.com/watch?v=0xt5-FTpASM

On top of the theory’s mathematical advantages, Stelle’s “sweet little scalar” is exactly the sort of particle (and associated quantum field) that could have driven an explosive expansion of the cosmos during the Big Bang, which many cosmologists believe set up the universe we see today. In fact, the Soviet physicist Alexei Starobinsky used quadratic gravity to formulate the first theory(opens a new tab) of that initial growth spurt, termed cosmic inflation, in 1980.

Through a combination of unexpectedly friendly ghosts, the growing popularity of Starobinsky inflation, and other quantum gravity theories languishing in the doldrums, quadratic gravity has grown in popularity. Stelle’s original paper(opens a new tab) has recently been accruing more than 150 citations each year.


https://www.quantamagazine.org/old-ghost-theory-of-quantum-gravity-makes-a-comeback-20251117/
 
Last edited:
You must log in or register to reply here.
Back
Top