Maybe I’m misinformed about this. But I was always told matter cannot be destroyed or created. But I have been told space is constantly expanding. Is this expansion of space not made up of “matter”? Where does it come from?
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The universe is expanding because it is being filled by dark matter. Dark matter is used up time.
I feel like this is missing as an ELI5: conservation of mass is mostly a chemistry idea. Mass is conserved in a CHEMICAL REACTION. Once you start getting into weird nuclear reactions and particle physics stuff, things get weird. But in our every day lives, mass IS conserved.
Space is not matter.
The expansion of space is just a property that it has. It’s one of the mysteries we are still trying to solve.
Think of space expanding like blowing up a balloon. The balloon gets bigger as it keeps inflating. If you were to draw two dots on the surface of the balloon, no matter where you draw them, they will get further apart from each other as the balloon expands. That’s how space is expanding. Everything is getting further away from everything else, all the time.
At a small scale, gravity pulls it all back together, but at a larger scale the expansion of space means that every galaxy, every star, is rushing away from every other galaxy and every other star all the time. Eventually, trillions of years from now, expansion will make objects in space so far apart that we won’t even be able to see anything outside of our local area.
That phase commonly comes from a chemistry teacher and neglects a few key words: in a chemical reaction matter can’t be created or destroyed. Others have already explained that matter can indeed be created and destroyed; we do it all the time!
This is one of my favorite fun facts when giving tours (particle physics)
Space is just emptiness. Space isn’t made up of anything. It’s a place in which matter exists.
Energy/matter conservation laws do apply, but spacetime is a different entity that can expand/contract without violating said laws.
Stretch an uncooked pizza and the pepperoni will be further apart, imagine the pepperoni is glued onto the dough and the dough can only be broken by black holes. Eventually the stretching of the dough will break the pepperoni, and then it’s atomic particles.
The dough stretches forever and gets faster as time goes on. The heat death of the pizza is when the dough is so stretched, the particles that made up the atoms of the pepperoni are stretched too far for their interactive forces to work.
Everything is getting further apart.
Imagine you and some friends meet up in a circle in the center of a football field. Then each of you takes a step back, then another. The size of your circle is increasing with every step (eventually it will be the entire football field), but no new friends have been created. You’re just all getting further apart.
If you boil water it expands because the distance between each molecule increases with more heat applied, they energetically bounce off each other. Spacetime is made up of sub-atomic particles that ‘fizz’ in and out of existence it is not ‘matter’ as we know it, it is a framework that permits the production of matter, we can’t say they are ‘expanding into’ something like water molecules expand into air because physics doesn’t have a model for anything other than spacetime and sub-atomic particles (string theory attempts to describe the ‘reality’ of sub-atomic particles with something called ‘super-position’ which is a theory, there is no practical evidence for super-position). The most commonly accepted theory for spacetime is Quantum Field Theory: [https://en.wikipedia.org/wiki/Quantum_field_theory](https://en.wikipedia.org/wiki/Quantum_field_theory)
Spacetime appears to expand from our perspective because of the way they measure distance from observer to object being viewed, that is what Relativity means, what we see is relative to the viewers position in spacetime, our particular frame of reference. It doesn’t mean that spacetime may not appear static from a different perspective. A black hole, or more accurately a singularity, is a point in spacetime with infinite density and zero dimensions. It’s gravitational effects are what increase but it’s physical size doesn’t. We can only describe a singularity from it’s event horizon which is the boundary between known spacetime and whatever is inside, inside the event horizon known physics breaks down. There are physicists who have postulated that our universe exists inside a black hole.
There is a theory, largely rejected now, called ‘Tired Light’ that says that the redshift of light maybe the effect of light passing through spacetime rather than the emitter (the star) actually moving, in which case apparent expansion of spacetime would be an optical illusion rather than a reality. The theory was rejected because it didn’t fit all observations made of interstellar objects, but again that is not to say that there may be other reasons for those anomalies that we just don’t know about yet and recently a scientific paper was published that suggested a mix between Doppler Shift redshift and ‘Tired Light’ could explain current JWST observations.
So we have to accept the fact that we can describe what we see from our perspective but we do not absolutely know what is happening to spacetime, or whatever ‘may be’ outside of known spacetime, and we only have theoretical postulates about what exactly spacetime is.
The word ‘expanding’ is simply the most appropriate way to describe what we see from our current perspective. The theory of expansion still leaves many many questions unanswered (which is why they postulate ‘Dark Energy’, in scientific terms ‘Dark’ means ‘we have no idea what it actually is and how it is formed’ but there is no other model that fits observations better). The only thing we can say with literal certainty is that observations of stellar objects appear to have more and more Redshift the higher the resolution of the viewing equipment, from this current theory extrapolates that higher viewing resolution means greater distance and apparent Redshift / Blueshift currently only has one testable cause as far as we know, that of movement (acceleration) of the emitter relative to the viewer through spacetime.
Why assume spacetime expansion? Because otherwise some force must be pushing galaxies apart counteracting the gravity between those galaxies and galaxy clusters. The observed phenomenon described as Spacetime Expansion does not appear to be affected by gravity (unless it’s very local) because it’s effect is increasing with distance, the further away the faster the galaxies are moving away (this is what Redshift is), indeed observations suggest that at some point in the past it actually sped up, not slowed down.
It’s the model that best fits what we see according to the consensus of the scientific community, remember they were the one’s who also thought that Einsteins theory of Special Relativity was a fringe theory initially until someone went out and watched the transit of Mercury around the Sun and did some now ‘suspect calculations’ to make observation fit the theory, however Special Relativity and General Relativity have proven to be the most accurate way to describe what is observed in the universe up to now, it’s not necessarily an absolutely correct and full explanation of what is actually happening.
We know the Theory of General Relativity is incomplete because it cannot describe what we see happening with sub-atomic particles, the very stuff the observable universe is made of. There is no ‘Grand Unifying Theory’. So for questions like, what is the universe expanding into and what is causing that ever accelerating expansion despite all the gobble-dee-gook the true answer is, we just don’t know, but it appears to be expanding from our frame of reference so there must be a cause… here’s our best guess. When they say ‘It isn’t expanding in to anything’ what they are saying is we have no frame of reference outside of the known universe, so there’s no practical way to talk about it or include it in any calculations.
There’s a few things to consider. To calculate distance to other stars they use 3 methods:
Basic triangulation using angles to measure distance, this only works very locally.
Another method is the ‘Standard Candle’ method that says type 1A Supernova’s have a standard brightness so when you observe a type 1A Supernova you can see how bright it is from our perspective and from that infer distance using the Inverse Square Law – most would be surprised how few type 1A supernova’s have been observed since this theory was developed.
From this Supernova data they calculate something called Lamda which is used to calculate distance using Doppler Shift (Doppler shift shows movement, the more the light is stretched the faster the object is accelerating away from you) – per Edwin Hubble – and Einstein who said that light has a constant speed in a vacuum no matter what frame of reference it is travelling in. This Lamda ‘constant’ has been revised and revised in light of observations since it was first postulated. This also makes the assumption that physics works the same wherever you are in the universe and that what we see isn’t just a local effect, when they describe the universe as ‘Flat’, this is what they are talking about, that the universe is the same, everything behaves the same according to General Relativity principles, everywhere… it isn’t proven beyond doubt because we can’t get outside of our local spacetime region to test it, we just haven’t found any evidence to say it isn’t.
By all means find out about current consensus thinking but the thing to pay attention to are the actual observations and explanations scientists come up with for those observations and keep asking questions, keep testing assumptions. That’s the difference between science and dogma.
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