Dark matter and entropy

[Interested amateur]

I'm a first time poster, work in communications (I do not consider myself a scientist but I'm fascinated by science) and I'd like to get the opinion of people who know what they're talking about. I’ve been thinking about dark matter and entropy.

My idea is that dark matter might not be a new particle at all, but instead matter from an older universe that has gone through or is going through heat death. In this framing, our universe is expanding into the fossilized remains of previous universes, whose matter still exerts gravitational influence but no longer interacts with light.

Would current cosmological models rule out this kind of “fossil universe” idea? And if matter in different stages of entropic decay could exist alongside ours, how would we expect it to interact with normal / detectable matter? I also reasoned that the expansion of the fossil universe(s) we're expanding into might be driving the accelerating expansion of our universe but I'm not going to push my luck with this idea .

I’d love to hear how trained astrophysicists would evaluate this kind of speculation. I'm also conscious that I'm not a trained scientist but I'm genuinely curious about your opinions and I've been impressed by the level of discussion around the other topics posted to this group that I've read.

 

[Pinball1970]

I'm a first time poster, work in communications (I do not consider myself a scientist but I'm fascinated by science) and I'd like to get the opinion of people who know what they're talking about. I’ve been thinking about dark matter and entropy.

My idea is that dark matter might not be a new particle at all, but instead matter from an older universe that has gone through or is going through heat death. In this framing, our universe is expanding into the fossilized remains of previous universes, whose matter still exerts gravitational influence but no longer interacts with light.

Would current cosmological models rule out this kind of “fossil universe” idea? And if matter in different stages of entropic decay could exist alongside ours, how would we expect it to interact with normal / detectable matter? I also reasoned that the expansion of the fossil universe(s) we're expanding into might be driving the accelerating expansion of our universe but I'm not going to push my luck with this idea .

I’d love to hear how trained astrophysicists would evaluate this kind of speculation. I'm also conscious that I'm not a trained scientist but I'm genuinely curious about your opinions and I've been impressed by the level of discussion around the other topics posted to this group that I've read.

Hi there, I'm a tech not a scientist either and I am also interested in science/physics.

Heat death involves matter decaying to radiation IIRC. The expanding universe (which may not be accelerating) will eventually stretch out the radiation till there is no longer any information, wavelength, frequency so nothing will ever change.

I am not sure what that would look like, if it would be detectable, if there is no information and everything is equilibrium probably not.
There is video of this, Brian Cox does the actual heat death part. Roger Penrose says mathematically that end state would be similar to a big bang scenario.
I don't know that would work, it is called CCC, Conformal Cyclic Cosmology.

 

[Pinball1970]

This is the short version, four minutes.

 

[Interested amateur]

Yes!!! I was watching the Brian Cox documentary and that's what inspired me. I had it stuck in my mind that particles in the early stages of heat death might exert a gravitational influence but not be detectible (not enough energy to release light). Obviously, our universe hasn't existed long enough for matter to enter into this state so the only alternative I could think of was that our universe is expanding within a much older one. The stumbling block I've hit is how would our universe emerge from the embers of a dying universe but from the very basic reading I've done it could be caused by fluctuations at a quantum level??? Whilst incredibly rare, given the vast timescales of particle heat death, a quantum fluctuation that could produce a big bang might become a probable rather than a possible occurrence. After all, isn't it more likely that something comes from something rather than something from absolute nothing? Trouble is, I'm completely untrained and this all exists in my head and not based in a sound mathematical reasoning.

 

[Pinball1970]

Yes!!! I was watching the Brian Cox documentary and that's what inspired me. I had it stuck in my mind that particles in the early stages of heat death might exert a gravitational influence but not be detectible (not enough energy to release light). Obviously, our universe hasn't existed long enough for matter to enter into this state so the only alternative I could think of was that our universe is expanding within a much older one. The stumbling block I've hit is how would our universe emerge from the embers of a dying universe but from the very basic reading I've done it could be caused by fluctuations at a quantum level??? Whilst incredibly rare, given the vast timescales of particle heat death, a quantum fluctuation that could produce a big bang might become a probable rather than a possible occurrence. After all, isn't it more likely that something comes from something rather than something from absolute nothing? Trouble is, I'm completely untrained and this all exists in my head and not based in a sound mathematical reasoning.

The heat death is a possible scenario and what happened before a certain time in the universe is also speculative.
Some cosmologists think the Universe most likely is eternal, I think Alan Guth is one of those, he came up with inflation theory.
Discussing this on other forums it was suggested that the universe is spatially infinite but temporarily finite which is not easy to get ones head around!

 

[Interested amateur]

It makes perfect sense. But then I suppose we're confronted with the question what is the universe. Can a universe be called a universe even after heat death when all that remains are ripples in the quantum substrata. Even a trillion trillion years is miniscule when compared to the vastness of infinity and as entropy grinds to an inexorable halt, does time. I know they're different but they're intrinsically linked - does time end as the universe fades to nothingness. I suppose the question that then pops into my head becomes; does the universe keep expanding infinitely in a closed system of maximum entropy. Is expansion a result of internal process (when all physical processes have ended) or external influence. Given that so much energy is unaccounted for (think it's 68% or there abouts), then my guess would be an external influence. Additionally, from my near obsessive watching of documentaries, I'm led to believe that dark energy is evenly distributed and that being the case, I reasoned that we're expanding within another universe that's also expanding. My query about whether dark matter and "fossil" matter being one and the same conveniently fits my narrative (and it really is just an interesting story at this point) but I've no idea if it holds any basis in observed cosmology but it would seem to be easily testable and disprovable.

 

[Pinball1970]

what is the universe

All that exists.

does time end as the universe fades to nothingness. I suppose the question that then pops into my head

There would be no way to measure time since there would be no systems. No earth and sun, no pulsars, no Caesium clocks and no beings with watches.

does time end as the universe fades to nothingness. I suppose the question that then pops into my head

If that is the fate of the universe then I would say yes.

but it would seem to be easily testable and disprovable.

How would you measure it?

 

[exchemist]

Yes!!! I was watching the Brian Cox documentary and that's what inspired me. I had it stuck in my mind that particles in the early stages of heat death might exert a gravitational influence but not be detectible (not enough energy to release light). Obviously, our universe hasn't existed long enough for matter to enter into this state so the only alternative I could think of was that our universe is expanding within a much older one. The stumbling block I've hit is how would our universe emerge from the embers of a dying universe but from the very basic reading I've done it could be caused by fluctuations at a quantum level??? Whilst incredibly rare, given the vast timescales of particle heat death, a quantum fluctuation that could produce a big bang might become a probable rather than a possible occurrence. After all, isn't it more likely that something comes from something rather than something from absolute nothing? Trouble is, I'm completely untrained and this all exists in my head and not based in a sound mathematical reasoning.

It looks to me as if the idea of dark matter being just ordinary matter that is too cold to radiate does not hold water. Obviously, this would have been one of the first ideas astronomers had to account for the rotation curve anomalies. But cold baryonic (i.e. conventional) matter would be backlit by stars behind it and would scatter light passing through it. This is not observed. Also, the theory of genesis of the elements would predict that if this were conventional baryonic matter, there should be a corresponding extra amount of hydrogen and helium, contrary to what is observed.

The relevant passage in the Wiki article is this one:

However, multiple lines of evidence suggest the majority of dark matter is not baryonic:

• Sufficient diffuse, baryonic gas or dust would be visible when backlit by stars.
• The theory of Big Bang nucleosynthesis predicts the observed abundance of the chemical elements. If there are more baryons, then there should also be more helium, lithium and heavier elements synthesized during the Big Bang.[109][110]Agreement with observed abundances requires that baryonic matter makes up between 4–5% of the universe's critical density. In contrast, large-scale structure and other observations indicate that the total matter density is about 30% of the critical density.[76]
• Astronomical searches for gravitational microlensing in the Milky Way found at most only a small fraction of the dark matter may be in dark, compact, conventional objects (MACHOs, etc.); the excluded range of object masses is from half the Earth's mass up to 30 solar masses, which covers nearly all the plausible candidates.[111][112][113][114][115][116]
• Detailed analysis of the small irregularities (anisotropies) in the cosmic microwave background by WMAP and Planckindicate that around five-sixths of the total matter is in a form that only interacts significantly with ordinary matter or photons through gravitational effects.[117]

From: https://en.wikipedia.org/wiki/Dark_matter

So I don't think the idea of a cold remnant of conventional matter, left over from a previous universe that has thermally run down, can be a good explanation.

 

[exchemist]

Hi there, I'm a tech not a scientist either and I am also interested in science/physics.

Heat death involves matter decaying to radiation IIRC. The expanding universe (which may not be accelerating) will eventually stretch out the radiation till there is no longer any information, wavelength, frequency so nothing will ever change.

I am not sure what that would look like, if it would be detectable, if there is no information and everything is equilibrium probably not.
There is video of this, Brian Cox does the actual heat death part. Roger Penrose says mathematically that end state would be similar to a big bang scenario.
I don't know that would work, it is called CCC, Conformal Cyclic Cosmology.

Is that right? How can matter decay to radiation?

I thought the matter just cools down so that everything is at the same temperature, in equilibrium with the effective black body "temperature" of the background radiation, so no thermodynamically driven change can take place.

 

[Interested amateur]

Is that right? How can matter decay to radiation?

I thought the matter just cools down so that everything is at the same temperature, in equilibrium with the effective black body "temperature" of the background radiation, so no thermodynamically driven change can take place.

Thank you for your excellent post! I remember reading about the 2nd law of thermodynamics ages ago (I went out with a girl who was studying astrophysics in university for a while). From what I remember entropy always increases in a closed system so eventually all matter ultimately gets converted into radiation. You're right that all matter gets colder but beyond that, matter itself loses cohesion as entropy continues to increase. Eventually all that remains is diffuse radiation. It's the state of maximum entropy. My original post is based on reading whether matter undergoing heat death retains mass enough to gravitationally interact with surrounding matter yet is undetectable due to it's inability to interact with light. I should say, I'm not referring to dead black holes & planets or even dust, I'm thinking of matter that's broken down into particles like protons, neutrinos & electrons that have mass but wouldn't interact with normal matter. In a stand alone universe this process has no impact & the universe simply evaporates into radiation after trillions & trillions of years. I'm not keen on the idea of a big rip but I'm a bigger fan of a big freeze and because of the time scales involved in evaporating matter down into it's constituent particles, in a young universe like ours you wouldn't expect to see any matter of this kind produced naturally. But if our universe was expanding into another much older one you might. I need to read through your counter point in detail. It's fascinating and thanks for taking the time to reply. Here's a video about heat death that I found that I keep thinking about:

.

 

[Pinball1970]

Is that right? How can matter decay to radiation?

Here are some possible mechanisms, proto decay has not been experimentally observed yet.

Proton decay - Wikipedia

en.wikipedia.org

Here is a quick search on the some of the projects involving proton decay.

IMB (Irvine-Michigan-Brookhaven): A past water-Cherenkov detector in the USA that set early limits on the proton lifetime and famously detected neutrinos from Supernova 1987A.
KamiokaNDE: A Japanese water-Cherenkov experiment that also set limits and detected supernova neutrinos; its successor is a leading current experiment.

Super-Kamiokande (Super-K): The currently largest operating water-Cherenkov detector in Japan, which provides the most stringent constraints on the proton lifetime to date.

Hyper-Kamiokande (Hyper-K): An upgraded, significantly larger water-Cherenkov detector currently under construction in Japan, with data taking expected to begin in 2027. Proton decay search is one of its primary objectives.

DUNE (Deep Underground Neutrino Experiment): A future liquid argon detector in the US which has proton decay search among its key goals.

JUNO (Jiangmen Underground Neutrino Observatory): A liquid scintillator detector under construction in China that also has the possibility to search for proton decay.

 

[exchemist]

Thank you for your excellent post! I remember reading about the 2nd law of thermodynamics ages ago (I went out with a girl who was studying astrophysics in university for a while). From what I remember entropy always increases in a closed system so eventually all matter ultimately gets converted into radiation. You're right that all matter gets colder but beyond that, matter itself loses cohesion as entropy continues to increase. Eventually all that remains is diffuse radiation. It's the state of maximum entropy. My original post is based on reading whether matter undergoing heat death retains mass enough to gravitationally interact with surrounding matter yet is undetectable due to it's inability to interact with light. I should say, I'm not referring to dead black holes & planets or even dust, I'm thinking of matter that's broken down into particles like protons, neutrinos & electrons that have mass but wouldn't interact with normal matter. In a stand alone universe this process has no impact & the universe simply evaporates into radiation after trillions & trillions of years. I'm not keen on the idea of a big rip but I'm a bigger fan of a big freeze and because of the time scales involved in evaporating matter down into it's constituent particles, in a young universe like ours you wouldn't expect to see any matter of this kind produced naturally. But if our universe was expanding into another much older one you might. I need to read through your counter point in detail. It's fascinating and thanks for taking the time to reply. Here's a video about heat death that I found that I keep thinking about:

.

Is there anything to suggest baryons decay into radiation though? I thought the proton and the electron were considered to be stable.

The Second Law of TD says that entropy, which is a term for how spread out thermal energy is, tends to a maximum. It says nothing about particle decay. The implication is that eventually everything will be at the same temperature.

Protons and electrons most certainly do interact with light, because they are electrically charged and have spin, which gives them a megnetic moment. So they will interact with electromagnetic radiation, which includes radio waves, infra red radiation, visible and UV light, X-rays, etc.

That's the point really. Normal matter, whether hot or cold, will emit, absorb or just scatter radiation, because it is made of charged magnetic particles.

 

[exchemist]

Here are some possible mechanisms, proto decay has not been experimentally observed yet.

Proton decay - Wikipedia

en.wikipedia.org

Here is a quick search on the some of the projects involving proton decay.

IMB (Irvine-Michigan-Brookhaven): A past water-Cherenkov detector in the USA that set early limits on the proton lifetime and famously detected neutrinos from Supernova 1987A.
KamiokaNDE: A Japanese water-Cherenkov experiment that also set limits and detected supernova neutrinos; its successor is a leading current experiment.

Super-Kamiokande (Super-K): The currently largest operating water-Cherenkov detector in Japan, which provides the most stringent constraints on the proton lifetime to date.

Hyper-Kamiokande (Hyper-K): An upgraded, significantly larger water-Cherenkov detector currently under construction in Japan, with data taking expected to begin in 2027. Proton decay search is one of its primary objectives.

DUNE (Deep Underground Neutrino Experiment): A future liquid argon detector in the US which has proton decay search among its key goals.

JUNO (Jiangmen Underground Neutrino Observatory): A liquid scintillator detector under construction in China that also has the possibility to search for proton decay.

But doesn't this really say there are theoretical grounds for believing the proton to be intrinsically stable, whereas all theories suggesting the contrary so far lack experimental support?

And then there is the electron. My understanding is this is thought to be stable as well.

So heat death would in that case be just thermodynamic run-down, not particle decay.

 

[Pinball1970]

lack experimental support?

I do not have a view particularly I just assumed this was part of the heat death scenario.
No mass remaining just "a sea of photons" in equilibrium.
There are several ways it could happen theoretically and there are projects to detect it.

That is as much as I know.

 

[Pinball1970]

I will add that with three projects under construction as well as the three existing detectors, some physicists seem motivated enough to be looking and these types of projects are not cheap to build and maintain.

 

[exchemist]

I do not have a view particularly I just assumed this was part of the heat death scenario.
No mass remaining just "a sea of photons" in equilibrium.
There are several ways it could happen theoretically and there are projects to detect it.

That is as much as I know.

I think a sea of photons and leptons, (i.e. including electrons and I suppose positrons for electrical charge balance), if the proton is not after all stable, as according to the Standard Model it is predicted to be.

From the quick reading I have done it looks as if some Grand Unified Theories would like the proton not to be stable. But so far none of these theories works! So right now I can't see how one can justify assuming protons will eventually decay in a heat death scenario. I suspect journo hype to make it seem more dramatically terminal - but maybe that's just my cynicism about these quasi-metaphysical speculations.

 

[Derek.H.]

Cosmo-Folk ,
It is suggested above that an expanding universe (ours) eventually runs into universes which "died" long ago .
The difficulty with this is that if said universes still contain any particles , we should experience a constant rain of directional and inexplicable relativistic particles , this possibly including matter aggregates (dust) if said universes were young enough .
Additionally , if the abovementioned universes were well past "heat-death" , then we should still experience a constant and directional stream of extremely high-energy electromagnetic-radiation , this/these with no other plausible explanation than that they are evidencing a high-speed universal collision .
Given that we are now well into the age of advanced imaging and radiation-detection , it seems likely that were the above extant , we would already have found evidence to that effect . The dearth of said evidence speaks volumes about the likelihood of the various "Cosmic-Cycling" paradigms being accurate , though it cannot eliminate these possible scenarios , as we have no idea what the relevant detection parameters should be .

*So , to encapsulate the above critique in facile layman's terminology :
"Why no cosmic poo-poo ?"

 

[TheVat]

My idea is that dark matter might not be a new particle at all, but instead matter from an older universe that has gone through or is going through heat death. In this framing, our universe is expanding into the fossilized remains of previous universes, whose matter still exerts gravitational influence but no longer interacts with light.

You're getting some good answers - I just want to add that leftover matter from such an older universe would still be, at minimum, leptons and therefore detectable. Also, per Poincare's recurrence theorem, a spontaneous entropy decrease could occur and from a fluctuation then jump-start another new universe. I guess this would change a thermodynamic heat death to a heat long nap.

 

[exchemist]

Cosmo-Folk ,
It is suggested above that an expanding universe (ours) eventually runs into universes which "died" long ago .
The difficulty with this is that if said universes still contain any particles , we should experience a constant rain of directional and inexplicable relativistic particles , this possibly including matter aggregates (dust) if said universes were young enough .
Additionally , if the abovementioned universes were well past "heat-death" , then we should still experience a constant and directional stream of extremely high-energy electromagnetic-radiation , this/these with no other plausible explanation than that they are evidencing a high-speed universal collision .
Given that we are now well into the age of advanced imaging and radiation-detection , it seems likely that were the above extant , we would already have found evidence to that effect . The dearth of said evidence speaks volumes about the likelihood of the various "Cosmic-Cycling" paradigms being accurate , though it cannot eliminate these possible scenarios , as we have no idea what the relevant detection parameters should be .

*So , to encapsulate the above critique in facile layman's terminology :
"Why no cosmic poo-poo ?"

Without subscribing to what is being proposed in the OP, I’d have thought that the remnants of any previous heat-dead universe would be cold and very diffuse. Why do you think there would be high energy radiation?

 

[Pinball1970]

I think a sea of photons and leptons, (i.e. including electrons and I suppose positrons for electrical charge balance), if the proton is not after all stable, as according to the Standard Model it is predicted to be.

I found this w.r.t. the fate of Leptons at the heat death.

• Electrons: These are stable and are expected to persist indefinitely.
• Neutrinos: These are also stable and, due to their very low mass and weak interactions, will simply drift apart.
• Muons and Tau particles: These are heavy, unstable leptons that rapidly decay into electrons and neutrinos over very short timescales, long before the heat death scenario.