B Conflict between the conservation of matter and the rapid expansion of our universe

[JedediahJones]

How did you find PF?: Google search.

I looked you up on google. A facebook group on Physics rejected my posting a question on the law of conservation of matter so I unfollowed and left group. I'm now here at this forum with the attitude one may entertain an idea without agreeing to it as the saying goes. I have few answers but a lot of questions. My first question is what seems to me to be a conflict with a law of physics. The particular law is the conservation of matter which states "matter cannot be created or destroyed in an isolated system." Edwin Hubble back in 1929 noted that our universe is rapidly expanding and it continues to do so as we observe to this very day with the Hubble Telescope. I understand Lemaître, a Belgian physicist, proposed the universe originated from an atom and expands like a balloon. To this day many scientists agree that existence is not expanding into something as there is nothing beyond. Dear reader one does not have to be a fortuneteller to foresee my obvious statement and question.

The law of conservation of matter is FALSE. Therefore matter can be created and can be destroyed in an isolated system. This is freely proven by all data with the hubble telescope and other sources that are observing the rapid expansion of our universe to this very day and beyond. Our universe is our reality we are told. Nothing exists beyond it, therefore expansion cannot be getting it's materials from beyond our universe. This is what our greatest minds are telling us.

If this is true then where are the materials coming from to expand our universe, much less expand it in an ever accelerating manner? The materials for new worlds etc new systems.. have to be coming from somewhere and they are not less dense than within our current universe or that of yesteryear.

Therefore is it likely that the "law" of conservation of matter is FALSE? That matter CAN be created and therefore destroyed?

IF it is true that matter can be created and destroyed our greatest minds might want to be all over this especially in regards to any other laws or theories that are based on the untruth.

So, both cannot be true, which one is true?

 

[Ibix]

Matter can be created and destroyed. That's how nuclear reactors work.

This has nothing to do with the expansion of the universe, where the amount of matter is finite and fixed if the universe is closed and infinite if it is open or flat.

 

[PeroK]

As the universe expands, the density of the matter in the universe reduces proportionally. This is a key factor in modeling the expansion rate.

 

[PeroK]

Note that in the expanding universe distant galaxies are, in general, getting further apart. No new galaxies are being created or destroyed as part of the expansion.

 

[weirdoguy]

IF it is true that matter can be created and destroyed our greatest minds might want to be all over this especially in regards to any other laws or theories that are based on the untruth.

I'm sorry, but the fact that "matter is not conserved" is known for decades and is even taught at high-school level physics. I don't want to sound rude, but before you go on a rant on 'what our greatest minds might want to be all over', learn physics and what is known in 2025 first

 

[JedediahJones]

Note that in the expanding universe distant galaxies are, in general, getting further apart. No new galaxies are being created or destroyed as part of the expansion.

Thank you. I had not considered this possibility. However in the growing distance there would not be literally nothingness right? There would in fact be asteroids and other bits of matter scattered about in the between, and those amounts would have to come from somewhere, meaning a reduction from that same somewhere? or not?

 

[Ibix]

AI summaries of physics are uniformly terrible.

Conservation of mass doesn't even apply to chemical reactions, strictly speaking, although you'd need a ridiculously precise balance to measure it. So conservation of mass is an extremely useful approximation (good enough that it took us until early last century to notice it wasn't correct) but isn't really true.

There would in fact be asteroids and other bits of matter scattered about in the between, and those amounts would have to come from somewhere, meaning a reduction from that same somewhere? or not?

No. There's almost certainly intergalactic matter, true, but its average density reduces over time at the same rate as the volume increases - the total mass is pretty much constant.

 

[JedediahJones]

Matter can be created and destroyed. That's how nuclear reactors work.

This has nothing to do with the expansion of the universe, where the amount of matter is finite and fixed if the universe is closed and infinite if it is open or flat.

Ibix, is it true that we as a species have 0 idea if the universe is closed or open? It's just any persons guess or ..faith?

 

[JedediahJones]

AI summaries of physics are uniformly terrible.

Conservation of mass doesn't even apply to chemical reactions, strictly speaking, although you'd need a ridiculously precise balance to measure it. So conservation of mass is an extremely useful approximation (good enough that it took us until early last century to notice it wasn't correct) but isn't really true.

No. There's almost certainly intergalactic matter, true, but its average density reduces over time at the same rate as the volume increases - the total mass is pretty much constant.

Sometimes I feel like my ignorance is infinite(lol) however if you will indulge me a bit ..who is responsible for measuring this change in galactic density and using what instruments? Also, precisely how much has galactic density been reduced in the time Humanity has been aware?

 

[Ibix]

Ibix, is it true that we as a species have 0 idea if the universe is closed or open?

Current measurements don't exclude any of the three options, although if it's not flat it is very, very large.

It's just any persons guess

Our current best hypotheses suggest that the universe is driven towards flatness, so that's where the smart money is. But it remains an open question.

who is responsible for measuring this change in galactic density and using what instruments?

Telescopes. Due to the finite speed of light, when you look at things far away you see how things were a long time ago. And we can see everything moving away from us in a way consistent with a uniform expansion. And there is also evidence like the cosmic microwave background, the remains of the glow from the early hot dense state of the universe.

Also, precisely how much has galactic density been reduced in the time Humanity has been aware?

Practically no change on such a short timescale. However, as above, our telescopes let us see far back in time.

 

[PeroK]

Thank you. I had not considered this possibility. However in the growing distance there would not be literally nothingness right? There would in fact be asteroids and other bits of matter scattered about in the between, and those amounts would have to come from somewhere, meaning a reduction from that same somewhere? or not?

I'm not sure I understand the question. In Newtonian physics (space and time) and in Special Relativity spacetime is an unchanging background in which physics plays out. In General Relativity, spacetime itself has a dynamic character - spacetime itself plays a dynamic role. In particular, the universe is expanding over time. It's not expanding into otherwise empty space. When we consider the entire universe, the "expansion" is different from what we normally think of as an expansion - where a physical object expands to take up more space. In the model of the expanding universe, it's space itself that is expanding.

If the universe is spatially infinite, then it remains spatially infinite, but over time the galaxies get further apart from each other. This is not a problem to describe mathematically, although it can cause some conceptual problems if you are looking for an analogy from everyday life.

If the universe is large and finite, then it must curve in on itself. Again, mathematically this is not a problem, as four dimensional manifolds can be studied mathematically. But, again, conceptually the idea that this sort of abstract geometry applies to the space and spacetime we inhabit can be difficult to grasp.

In either case, nothing is being created or destroyed. In the simplest terms, the distance between distant objects gets larger over time. And this is the best model we have - the one that best fits the cosmologiocal data.

Note that the British cosmologist, Fred Hoyle, promoted a steady-state theory for years and did all sorts of mathematical tricks to try to make it fit the data. But, eventually, it became impossible to justify a steady-state universe, as the data mounted up against it. This is the way physics works. The Big Bang theory isn't an edict that was promoted without experimental evidence. It, like any modern physics theory, only became established once the data in support of it became difficult to refute. That said, there remain unanswered questions and the research goes on.

 

[TensorCalculus]

A common analogy is that the expansion of the universe is like a balloon being blown up (this analogy is definitely not a perfect representation how the expansion of the universe works but it's useful here) - every point gets farther apart from each other. Note that the mass of the balloon (rubber) does not change by being blown up, it just gets more and more stretched out. The rate of expansion of the universe is approximately 70km/s/Mpc (Mpc means one megaparsec - it's a unit of distance about $3.26156x10^6$ lightyears if my memory serves me right). That means 2 points will on average get 70km farther apart for every Mpc of distance between them every second (ignoring relativity, which needs to be factored in at larger distances). The key thing is that there's nothing created, everything's just being more spread out.

 

[berkeman]

A common analogy is that the expansion of the universe is like a balloon being blown up (this analogy is definitely not a perfect representation how the expansion of the universe works but it's useful here)

See this PF Insights article by @phinds for more detailed info about that analogy:

https://www.physicsforums.com/insights/balloon-analogy-good-bad-ugly/

 

[weirdoguy]

Respectfully, Google AI claims something a bit different

I don't care what AI says, and I'm not gonna discuss with it (and for your interest - it's talking about something different than you and I did).

Besides - using AI here is forbidden. Use other sources instead, books, and peer-reviewed papers.

 

[Ibix]

Note that the mass of the balloon (rubber) does not change by being blown up, it just gets more and more stretched out.

Worth pointing out that if you are making the analogy like this, the balloon is not a metaphor for space (which doesn't have any material structure to stretch in the first place). Rather, the atoms of the balloon represent galaxies, moving further and further apart.

That means 2 points will on average get 70km farther apart for every Mpc of distance between them every second (ignoring relativity, which needs to be factored in at larger distances)

I would be careful phrasing it like that. The expansion is already a relativistic phenomenon, and it would be a relativistic phenomenon in a hypothetical universe where Hubble's Law holds out to infinity. Deviation from the simple $v=Hd$ law at large distances comes about because the rate of change of the scale factor is not constant throughout the history of the universe.

 

[berkeman]

Respectfully, Google AI claims something a bit different. Is it wrong in your opinion?
AI Overview

Please check your DMs. AI chatbots are not valid references for use at PF.

 

[TensorCalculus]

Worth pointing out that if you are making the analogy like this, the balloon is not a metaphor for space (which doesn't have any material structure to stretch in the first place). Rather, the atoms of the balloon represent galaxies, moving further and further apart.

I would be careful phrasing it like that. The expansion is already a relativistic phenomenon, and it would be a relativistic phenomenon in a hypothetical universe where Hubble's Law holds out to infinity. Deviation from the simple $v=Hd$ law at large distances comes about because the rate of change of the scale factor is not constant throughout the history of the universe.

My bad, yeah I wasn't too clear on that one. Thanks for clarifying it! :D

 

[PeterDonis]

There would in fact be asteroids and other bits of matter scattered about in the between

Yes.

those amounts would have to come from somewhere

In the sense that they probably used to be part of some planetary system in some galaxy, yes. But not in the sense of just being created out of nothing. That's impossible.

There is a local conservation law in General Relativity, which is best described as a law of conservation of stress-energy. "Matter" is one component of stress-energy, but not the only one. It is possible to convert one form of stress-energy to another (for example, matter and antimatter can annihilate each other to produce radiation), but you can't just create stress-energy out of nothing, or destroy stress-energy and leave nothing behind.

 

[Nugatory]

A digression that was unhelpful to the thread and served only to make unnecessary work for the forum moderators has been removed.
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