Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

When I was at school the “nothing “ between the nucleus and the edge of a cell was called the cytoplasm.

Or do you mean the nothing between the nucleus and the edge of an atom?

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

Did he mean the “Nothing between the nucleus and the edge of the atom”?

I would suggest that the various kinds of “nothing” are due to “Nothing” being a versatile word.

“There is nothing in the bucket” – the bucket has no water, but contains air.
“There is nothing in the vacuum of space” – there is no matter, but there is still energy.
“There is nothing between the nucleus of an atom and the electron shell” – there may be no matter or energy, but there is still’space-time’
“The nothing that the universe is expanding into” – The universe is not expanding into anything. No matter, no energy, no ‘space-time’. Nothing.

yes atom… my mistyping.

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

gack! what a poor choice of terms – space isn’t ‘expanding’ into anything

Carmen_Sandiego said:

Did he mean the “Nothing between the nucleus and the edge of the atom”?

I would suggest that the various kinds of “nothing” are due to “Nothing” being a versatile word.

“There is nothing in the bucket” – the bucket has no water, but contains air.
“There is nothing in the vacuum of space” – there is no matter, but there is still energy.
“There is nothing between the nucleus of an atom and the electron shell” – there may be no matter or energy, but there is still’space-time’
“The nothing that the universe is expanding into” – The universe is not expanding into anything. No matter, no energy, no ‘space-time’. Nothing.

so.. nothing comes from some nothings, but something may come from other nothings and other nothings are really nothing, as in the absence of something.

diddly-squat said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

gack! what a poor choice of terms – space isn’t ‘expanding’ into anything

so it’s not nothing, it’s ‘not anything’

Arts said:

diddly-squat said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell is different to the nothing that space is expanding into”

are there different types of nothing?
how many types of nothing are there?
how are they different?

gack! what a poor choice of terms – space isn’t ‘expanding’ into anything

so it’s not nothing, it’s ‘not anything’

it’s the ‘into’ bit that causes the most confusion… space is expanding, but it isn’t expanding in the sense that it is growing to fill some otherwise unoccupied volume.

Moreover, the ruler that defines the size of the universe isn’t getting longer, it’s the the distance between the notches that is getting larger (but even that is a pretty crappy analogy)

diddly-squat said:

Arts said:

diddly-squat said:

gack! what a poor choice of terms – space isn’t ‘expanding’ into anything

so it’s not nothing, it’s ‘not anything’

it’s the ‘into’ bit that causes the most confusion… space is expanding, but it isn’t expanding in the sense that it is growing to fill some otherwise unoccupied volume.

Moreover, the ruler that defines the size of the universe isn’t getting longer, it’s the the distance between the notches that is getting larger (but even that is a pretty crappy analogy)

it’s expanding within the space it currently occupies?

Arts said:

diddly-squat said:

Arts said:

so it’s not nothing, it’s ‘not anything’

it’s the ‘into’ bit that causes the most confusion… space is expanding, but it isn’t expanding in the sense that it is growing to fill some otherwise unoccupied volume.

Moreover, the ruler that defines the size of the universe isn’t getting longer, it’s the the distance between the notches that is getting larger (but even that is a pretty crappy analogy)

it’s expanding within the space it currently occupies?

Think about space as an infinite volume… as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing.

diddly-squat said:

Arts said:

diddly-squat said:

it’s the ‘into’ bit that causes the most confusion… space is expanding, but it isn’t expanding in the sense that it is growing to fill some otherwise unoccupied volume.

Moreover, the ruler that defines the size of the universe isn’t getting longer, it’s the the distance between the notches that is getting larger (but even that is a pretty crappy analogy)

it’s expanding within the space it currently occupies?

Think about space as an infinite volume… as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing.

so the universe is just getting fatter?

>so the universe is just getting fatter?

Au contraire, it’s becoming less dense with time.

Arts said:

diddly-squat said:

Arts said:

it’s expanding within the space it currently occupies?

Think about space as an infinite volume… as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing.

so the universe is just getting fatter?

no, same amount of mass… for a given (intergalactic) volume the energy density is decreasing over time

I don’t know of any evidence that the Universe is not expanding into something.

diddly-squat said:

Arts said:

diddly-squat said:

Think about space as an infinite volume… as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing.

so the universe is just getting fatter?

no, same amount of mass… for a given (intergalactic) volume the energy density is decreasing over time

ok. this doesn’t make any real sense.

Arts said:

diddly-squat said:

Arts said:

so the universe is just getting fatter?

no, same amount of mass… for a given (intergalactic) volume the energy density is decreasing over time

ok. this doesn’t make any real sense.

Of course not, it’s astrophysics.

The Rev Dodgson said:

I don’t know of any evidence that the Universe is not expanding into something.

Thank you Rev… 8/

nor is there any evidence to suggest it isn’t – fact is we are causally disconnected from anything outside out Hubble Volume, so for the most part this is conversation mere CTM

The Rev Dodgson said:

I don’t know of any evidence that the Universe is not expanding into something.

Show us some sign of the something it might be expanding into, and it might be worth debating.

Arts said:

diddly-squat said:

Arts said:

so the universe is just getting fatter?

no, same amount of mass… for a given (intergalactic) volume the energy density is decreasing over time

ok. this doesn’t make any real sense.

the mass doesn’t change… the universe isn’t “putting on weight” so to speak… but if we look at a discrete volume (let’s call that volume our visible universe – it’s everything we can see) the energy density (a fancy way of describing the stuff matter is made up of) of this volume is decreasing. That is there is a tendency towards less energy density per unit volume over time.

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

>ok. this doesn’t make any real sense.

Picture a white screen, which is the early, dense universe. As it expands, little black dots of empty space appear amongst all the white, and gradually grow wider. Move further away from the screen and you see the white bits eventually turn into little white dots which move further apart as the black increases. It’s becoming less dense as it expands, because more and more empty space opens up.

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

There don’t appear to be any edges. The expansion of space causes more empty space to be created inside the universe. It doesn’t need to come from somewhere outside.

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

dude… here’s the bender… there no edges

Bubblecar said:

>ok. this doesn’t make any real sense.

Picture a white screen, which is the early, dense universe. As it expands, little black dots of empty space appear amongst all the white, and gradually grow wider. Move further away from the screen and you see the white bits eventually turn into little white dots which move further apart as the black increases. It’s becoming less dense as it expands, because more and more empty space opens up.

that did it…

thanks Bubblecar.

diddly-squat said:

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

dude… here’s the bender… there no edges

And “ Oh my God! It’s full of stars!”

Bubblecar said:

The Rev Dodgson said:

I don’t know of any evidence that the Universe is not expanding into something.

Show us some sign of the something it might be expanding into, and it might be worth debating.

What do you mean?

How could there be any sign of something we can’t observe?

>>more empty space to be CREATED

I see.

Bubblecar said:

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

There don’t appear to be any edges. The expansion of space causes more empty space to be created inside the universe. It doesn’t need to come from somewhere outside.

Neither do there appear to be not any edges.

We don’t know whether there are any edges or not.

The Rev Dodgson said:

Bubblecar said:

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

There don’t appear to be any edges. The expansion of space causes more empty space to be created inside the universe. It doesn’t need to come from somewhere outside.

Neither do there appear to be not any edges.

We don’t know whether there are any edges or not.

the ‘white screen’ could be almost infinite?

:)

>Neither do there appear to be not any edges.

If we can’t see any, it makes sense to try to build models that don’t have any. This has been done and the models work, and fit with our observations. There’s nothing wrong with speculation but to be taken seriously you’d have to design models in which the “edges” are physically described and properly accounted for etc.

The Rev Dodgson said:

Bubblecar said:

Arts said:

the bits of the universe are getting further apart, but the edges may or may not be moving into something, which may or may not be nothing or the absence of something.

There don’t appear to be any edges. The expansion of space causes more empty space to be created inside the universe. It doesn’t need to come from somewhere outside.

Neither do there appear to be not any edges.

We don’t know whether there are any edges or not.

Maybe it’s time to distinguish between our model of the universe and what ultimately may be the reality of the situation.

The current model of the universe proposes a space defined by an infinite, unbounded volume.

it’s a difficult concept to get the mind around.. I think we humans like to know that there’s an end point.

Arts said:

it’s a difficult concept to get the mind around.. I think we humans like to know that there’s an end point.

Oui, we live in a finite world- everything around us dies at some point so to have “nothing” is an alien concept.

Bubblecar said:

>Neither do there appear to be not any edges.

If we can’t see any, it makes sense to try to build models that don’t have any. This has been done and the models work, and fit with our observations. There’s nothing wrong with speculation but to be taken seriously you’d have to design models in which the “edges” are physically described and properly accounted for etc.

Our visible universe is very clearly defined by an edge, past that it’s open to speculation and may or may not be influenced by the assumption that the behavior of the bits we can’t see is the same as the behavior of the bits we can.

Arts said:

it’s a difficult concept to get the mind around.. I think we humans like to know that there’s an end point.

I think mostly people like to ‘believe’ what they can mentally visualise

>Our visible universe is very clearly defined by an edge

Yes but we understand the nature of that edge, which is an empirical constraint that effects any observer, wherever they are. It’s not the same as the idea that the universe is expanding into something external.

Bubblecar said:

>Our visible universe is very clearly defined by an edge

Yes but we understand the nature of that edge, which is an empirical constraint that effects any observer, wherever they are. It’s not the same as the idea that the universe is expanding into something external.

tots

…except I should have said affects, not effects :)

Bubblecar said:

>Neither do there appear to be not any edges.

If we can’t see any, it makes sense to try to build models that don’t have any. This has been done and the models work, and fit with our observations. There’s nothing wrong with speculation but to be taken seriously you’d have to design models in which the “edges” are physically described and properly accounted for etc.

The models fit equally well with a very large Universe with edges.

The models provide no evidence for whether the Universe has edges or not.

To state that the universe does not have edges (or boundaries, as I’d prefer to call them) as a statement supported by observational evidence is just wrong.

Why are people so reluctant to accept that we don’t know, and have no way of knowing?

diddly-squat said:

The current model of the universe proposes a space defined by an infinite, unbounded volume.

There is no one model of the Universe.

Our observations and models give zero evidence as to whether the Universe is finite or infinite, and if it is finite whether it has special boundaries or not.

>The models fit equally well with a very large Universe with edges.

What are your edges made of, in what way do they delineate a distinction between “the universe” and something that isn’t the universe, where did they come from etc? The models without edges don’t have to address any such questions, but the models with edges do. And AFAIA you’ve never made any attempt to provide any of those details.

The Rev Dodgson said:

Why are people so reluctant to accept that we don’t know, and have no way of knowing?

I’m less sure people are reluctant, well I’m not at least, to accept that we simply “don’t know for sure”… but in the mean time we need a model for the universe so we can continue to make predictions and then test those predictions against observation. It’s just the way science rolls…

The Rev Dodgson said:

diddly-squat said:

The current model of the universe proposes a space defined by an infinite, unbounded volume.

There is no one model of the Universe.

Our observations and models give zero evidence as to whether the Universe is finite or infinite, and if it is finite whether it has special boundaries or not.

OK… I agree that there are several models that may be, at the very least, equally likely. But I’d be surprised if most astrophysicists didn’t have a preferred model.

diddly-squat said:

Arts said:

it’s a difficult concept to get the mind around.. I think we humans like to know that there’s an end point.

I think mostly people like to ‘believe’ what they can mentally visualise

that’s interesting.

Bubblecar said:

>The models fit equally well with a very large Universe with edges.

What are your edges made of, in what way do they delineate a distinction between “the universe” and something that isn’t the universe, where did they come from etc? The models without edges don’t have to address any such questions, but the models with edges do. And AFAIA you’ve never made any attempt to provide any of those details.

We have no way of knowing these things. How could we have with no way of observing them?

There are any number of possibilities that would be consistent with what we can observe.

For instance, matter might just reduce in density to zero, in a similar way to the atmosphere around a planet.

The Rev Dodgson said:

Why are people so reluctant to accept that we don’t know, and have no way of knowing?

we like to know…

diddly-squat said:

The Rev Dodgson said:

… but in the mean time we need a model for the universe so we can continue to make predictions and then test those predictions against observation. It’s just the way science rolls…

We need a model for what we can observe.

Making up a model for what we can’t observe, and insisting that that is the way it is, is anti-productive to say the least.

Arts said:

The Rev Dodgson said:

Why are people so reluctant to accept that we don’t know, and have no way of knowing?

we like to know…

But we shouldn’t pretend we know things we don’t know.

I’m not suggesting for one moment that the models we have are complete and perfectly accurate etc. It’s just that if you want to suggest alternatives, they have to be as detailed and mathematically sound as the current preferred models.

As for the real universe, I suspect we’ll never have empirical access to enough of it to be able to achieve a complete cosmology.

Arts said:

diddly-squat said:

Arts said:

it’s a difficult concept to get the mind around.. I think we humans like to know that there’s an end point.

I think mostly people like to ‘believe’ what they can mentally visualise

that’s interesting.

the problem is that abstract concepts are unintuitive by their very nature

as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing
—————————
What is the scientific definition of “not bound gravitationally”?

Bubblecar said:

I’m not suggesting for one moment that the models we have are complete and perfectly accurate etc. It’s just that if you want to suggest alternatives, they have to be as detailed and mathematically sound as the current preferred models.

As for the real universe, I suspect we’ll never have empirical access to enough of it to be able to achieve a complete cosmology.

I’m not suggesting an alternative.

I’m saying that current models say nothing about whether the Universe is finite or infinite, and if it is finite whether it has spacial boundaries.

The Rev Dodgson said:

Arts said:

The Rev Dodgson said:

Why are people so reluctant to accept that we don’t know, and have no way of knowing?

we like to know…

But we shouldn’t pretend we know things we don’t know.

There are known unknowns.

The Rev Dodgson said:

diddly-squat said:

The Rev Dodgson said:

… but in the mean time we need a model for the universe so we can continue to make predictions and then test those predictions against observation. It’s just the way science rolls…

We need a model for what we can observe.

Making up a model for what we can’t observe, and insisting that that is the way it is, is anti-productive to say the least.

Now you’re just being deliberately obtuse.

Ian said:

Now you’re just being deliberately obtuse.

Why do you say that?

>I’m saying that current models say nothing about whether the Universe is finite or infinite, and if it is finite whether it has spacial boundaries.

Au contraire, the models themselves say a lot about such things :)

Whether they’re right or not is another matter.

Stealth said:

What is the scientific definition of “not bound gravitationally”?

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

The Rev Dodgson said:

Ian said:

Now you’re just being deliberately obtuse.

Why do you say that?

Dunno.. devil made me do it..

Bubblecar said:

>I’m saying that current models say nothing about whether the Universe is finite or infinite, and if it is finite whether it has spacial boundaries.

Au contraire, the models themselves say a lot about such things :)

Whether they’re right or not is another matter.

No, they don’t.

All models we have would provide identical predictions for:
- An infinite universe
- A sufficiently large finite universe without boundaries
- A sufficiently large finite universe with boundaries

Arts said:

it’s expanding within the space it currently occupies?

Imagine a balloon. Imagine the entire 3-dimensional universe on the surface of that balloon. Imagine the balloon being inflated. The universe gets bigger. That is kinda what is happening.

The relationship between distance, gravity and expansion is described by various equations. You’ll need the maths eggheads to explain them in detail :)

>All models we have would provide identical predictions for: – An infinite universe – A sufficiently large finite universe without boundaries – A sufficiently large finite universe with boundaries

No, those are different models. The unbounded models don’t have to include details that would be required of the bounded models. If the boundaries aren’t there, you don’t need to describe and account for them. i.e., the unbounded models are simpler.

…I know nothink

<BR>

..does anyone?

diddly-squat said:

Stealth said:

What is the scientific definition of “not bound gravitationally”?

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

Does that mean that they could still technically influence each other gravitationally though?

The Rev Dodgson said:

Bubblecar said:

>I’m saying that current models say nothing about whether the Universe is finite or infinite, and if it is finite whether it has spacial boundaries.

Au contraire, the models themselves say a lot about such things :)

Whether they’re right or not is another matter.

No, they don’t.

All models we have would provide identical predictions for:
- An infinite universe
- A sufficiently large finite universe without boundaries
- A sufficiently large finite universe with boundaries

I’m not sure that entirely true… the issue is that there is sufficient measurement error in the determination of the physical constants used to describe the models that we can’t be sure which way the needle falls, so to speak.

>Does that mean that they could still technically influence each other gravitationally though?

If the universe wasn’t expanding. But because it’s expanding, they can’t :)

Stealth said:

diddly-squat said:

Stealth said:

What is the scientific definition of “not bound gravitationally”?

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

Does that mean that they could still technically influence each other gravitationally though?

of course, the influence of gravity extends out to infinity

(..thought that you must have been playing silly buggers with the tags Rev)

Bubblecar said:

>All models we have would provide identical predictions for: – An infinite universe – A sufficiently large finite universe without boundaries – A sufficiently large finite universe with boundaries

No, those are different models. The unbounded models don’t have to include details that would be required of the bounded models. If the boundaries aren’t there, you don’t need to describe and account for them. i.e., the unbounded models are simpler.

No, the models are models of what we can observe, or of things that can indirectly affect what we observe.

All the models of the Universe that are consistent with our observations are consistent with both bounded and unbounded universes.

diddly-squat said:

I’m not sure that entirely true… the issue is that there is sufficient measurement error in the determination of the physical constants used to describe the models that we can’t be sure which way the needle falls, so to speak.

And so long as an infinite universe remains a possibility, there always will be.

Ian said:

(..thought that you must have been playing silly buggers with the tags Rev)

What tags?

>All the models of the Universe that are consistent with our observations are consistent with both bounded and unbounded universes.

You don’t seem to know what “model” means in this context. There are lots of different ones to choose from.

What you’re talking about is the empirical data, which is consistent with a variety of models

>What you’re talking about is the empirical data, which is consistent with a variety of models

….the preferred models tend to be those that don’t raise a lot of unanswerable questions that are not demanded by the evidence.

Bubblecar said:

>All the models of the Universe that are consistent with our observations are consistent with both bounded and unbounded universes.

You don’t seem to know what “model” means in this context. There are lots of different ones to choose from.

What you’re talking about is the empirical data, which is consistent with a variety of models

I suspect that I’m much more familiar with the scientific use of models than you are.

Bubblecar said:

>What you’re talking about is the empirical data, which is consistent with a variety of models

….the preferred models tend to be those that don’t raise a lot of unanswerable questions that are not demanded by the evidence.

All models raise an infinite number of unanswerable questions about what exists outside the limit where the model can be checked by observation.

The Rev Dodgson said:

Ian said:

(..thought that you must have been playing silly buggers with the tags Rev)

What tags?

Now you’re just being deliberately obtuse.

Ian said:

The Rev Dodgson said:

Ian said:

(..thought that you must have been playing silly buggers with the tags Rev)

What tags?

Now you’re just being deliberately obtuse.

I have no idea what you are on about.

>I suspect that I’m much more familiar with the scientific use of models than you are.

Then you’d know that there are different specific models, some of which are finite, some infinite, some flat, some collapsing, some without boundaries, some with etc and that they are therefore not all “consistent with both bounded and unbounded universes”. If there are no boundaries in the model, there are no boundaries in the model. If there are boundaries, then there are all kinds of theoretical questions raised by the model that don’t appear in the unbounded ones.

>All models raise an infinite number of unanswerable questions about what exists outside the limit where the model can be checked by observation.

Not if you design a model that deliberately avoids unanswerable questions that are not demanded by the evidence. Occam’s razor & all that :)

Stealth said:

diddly-squat said:

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

Does that mean that they could still technically influence each other gravitationally though?

Depends – If the current assumption that gravity acts at the speed of light is correct, then the parts of the universe are travelling away from each other at faster than the speed of light can not affect each other.

The Rev Dodgson said:

Ian said:

The Rev Dodgson said:

What tags?

Now you’re just being deliberately obtuse.

I have no idea what you are on about.

Rev, maybe you just need to leave your tag on the highest point of an obtuse hill…

Carmen_Sandiego said:

Stealth said:

diddly-squat said:

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

Does that mean that they could still technically influence each other gravitationally though?

Depends – If the current assumption that gravity acts at the speed of light is correct, then the parts of the universe are travelling away from each other at faster than the speed of light can not affect each other.

Oh good, I have now had a ‘no’ and a ‘yes’ and now a ‘maybe’.

But the yes and the maybe make sense.

Carmen_Sandiego said:

Stealth said:

diddly-squat said:

it’s the bits that expand away from each other because the influence of gravity is less than the ‘force’ driving expansion

Does that mean that they could still technically influence each other gravitationally though?

Depends – If the current assumption that gravity acts at the speed of light is correct, then the parts of the universe are travelling away from each other at faster than the speed of light can not affect each other.

changes in gravity act the SoL, but the influence of gravity is infinite in nature…

you all are arguing over nothing

runs away

CrazyNeutrino said:

you all are arguing over nothing

runs away

no

runs another way

Bubblecar said:

>All the models of the Universe that are consistent with our observations are consistent with both bounded and unbounded universes.

You don’t seem to know what “model” means in this context. There are lots of different ones to choose from.

What you’re talking about is the empirical data, which is consistent with a variety of models

Perhaps you should’ve been a little more diplomatic and said that TRD is using the word “model” in a slightly different way to the other posters in this thread…

Hopefully, TRD will agree that science does not attempt to describe the universe directly. Instead, it builds mathematical models and then explores how well the predictions derived from the models match up with empirical data.

The universe is a vast and complex thing, so it would be extremely difficult to create a single unified model that describes the whole thing; besides, such a model would be so unwieldy to work with that it’d be hard (if not downright impossible) to derive useful predictions from it.

So science adopts a “divide & conquer” strategy: the universe is analyzed as an interconnected system of components, and models are developed to describe each of these component parts and their interactions. When necessary, these components are further subdivided until we get to a level where the fundamental components can be adequately described by (relatively) simple mathematics.

Sometimes this division process is straight-forward, but with complex systems there’s always the danger that some significant details of the system will get lost in the process. This “divide & conquer” strategy has been very successful in the hard sciences like physics; it’s much harder to make it work effectively in biology.

So physics doesn’t really have a single model of the universe – it essentially uses nested families of models. Each level of a model family pretends that its components are very simple entities, leaving the fine details of these components to the next level down. Thus a theory that focuses on galaxy structure and formation pretends that individual stars are very simple things. It doesn’t care how stars actually work, it leaves the details to lower levels of the family of models.

At the highest level we have various cosmological models. These models (generally) treat the galaxies themselves as if they were ideal particles, like particles of dust, or the idealised atoms in an ideal gas. So we know that the toy universes modeled by cosmology are vastly simpler than the real universe, but hopefully these simplifications don’t significantly distort the behaviour that the models are intended to elucidate.

…

TRD has pointed out (in this and other threads) that we cannot empirically verify any of our models beyond the observable universe. But that’s ultimately a problem for philosophy: science has no business worrying about things that can never have an impact on empirical observation. And if new observations do turn up that contradict our current scientific theories, then we just have to modify or re-write our theories.

So science adopts Occam’s Razor and doesn’t bother modeling things that (it believes) can never influence our observations. Thus scientific models are (hopefully) as simple as they can be consistent with the empirical data.

Models of the cosmos that posit a spatial boundary to the universe are more complicated than models that do not have such boundaries, so Occam’s Razor tells us to prefer the boundary-free models, unless new data comes in that casts doubt on such models.

To give a simple mathematical example, we can describe a simple parabola with the equation
y = x²
But that parabola is infinite: it has a y value for every real x value. If we want to model a finite parabola our description needs to be more complicated,
eg
y = x², -1 <= x <= 1
We could also use a pair of parametric equations that allow our parameter to range over all real values, but that’s still more complicated than y = x².

….

I’m not clear on exactly what sort of boundary TRD is talking about. I suspect he’s talking about a “simple” boundary in space beyond which no matter exists, rather than a boundary of space beyond which space itself doesn’t exist. Modern cosmological models (generally) rule out both kinds of boundary, although the former type of boundary is less problematic than the latter. OTOH, with the first type of boundary, there would still be some energy beyond the matter limit, and if dark energy theory is correct, even space that’s devoid of matter and of its associated electromagnetic and gravitational energy still has some dark energy content, so there’s no such thing as totally empty space.

Still, both kinds of boundary make for a more complex theory that requires some explanation for these boundary conditions, as well as a (potentially much simpler) explanation for why we have no evidence for such boundaries within the observable universe.

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell an atom […]”

Even that’s misleading – there is no region inside an atom that’s permanently devoid of electrons.

>Models of the cosmos that posit a spatial boundary to the universe are more complicated than models that do not have such boundaries, so Occam’s Razor tells us to prefer the boundary-free models, unless new data comes in that casts doubt on such models.

Aye, as I bin sayin’.

>Perhaps you should’ve been a little more diplomatic and said that TRD is using the word “model” in a slightly different way to the other posters in this thread…

The Rev is used to my gruff ways :)

PM 2Ring said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell an atom […]”

Even that’s misleading – there is no region inside an atom that’s permanently devoid of electrons.

Electrons as billiard balls is SO classical 1920s

PM 2Ring said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell an atom […]”

Even that’s misleading – there is no region inside an atom that’s permanently devoid of electrons.

And there is only one electron… a very busy electron, but only one…

PM 2Ring said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell an atom […]”

Even that’s misleading – there is no region inside an atom that’s permanently devoid of electrons.

In all probability…

Stealth said:

And there is only one electron… a very busy electron, but only one…

Feynman was fond of that idea when he was still a student, but he decided that it’s probably not true, otherwise positrons would be far more common than they appear to be.

Dropbear said:

PM 2Ring said:

Arts said:

Dr Karl said “The nothing between the nucleus and edge of cell an atom […]”

Even that’s misleading – there is no region inside an atom that’s permanently devoid of electrons.

Electrons as billiard balls is SO classical 1920s

Yeah. And even if we do ignore the HUP and pretend that electrons have trajectories that obey classical physics, it’s still not right. Electrons in s orbitals have zero orbital angular momentum: their orbital momentum is purely radial. I.e., whenever you observe an s electron it’s moving directly towards or away from the nucleus, and QED says it has a non-zero probability of being located inside the nucleus itself. The s orbitals are the simplest orbitals, and every atom has some electrons in such orbitals.

PM 2Ring said:

QED says it has a non-zero probability of being located inside the nucleus itself.

That is my “Something weird I learned today” fact.

Carmen_Sandiego said:

PM 2Ring said:

QED says it has a non-zero probability of being located inside the nucleus itself.

That is my “Something weird I learned today” fact.

I read that fact a couple of nights ago in ‘Why Does E=MC^2’

Carmen_Sandiego said:

PM 2Ring said:

QED says it has a non-zero probability of being located inside the nucleus itself.

That is my “Something weird I learned today” fact.

Oh good. :)

An electron in an s orbitals is a bit like a bungy jumper in space. The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.

The exact probability function describing the electron’s mean distance from the nucleus is fairly simple for the inner s electrons, but it gets more complicated for the higher s orbitals.

The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.
—————————
That is such a cool analogy. I really like that, both for the concept it is trying to convey and the mental image of electrons tied into bungy harnesses.

PM 2Ring said:

Oh good. :)

An electron in an s orbitals is a bit like a bungy jumper in space. The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.

The exact probability function describing the electron’s mean distance from the nucleus is fairly simple for the inner s electrons, but it gets more complicated for the higher s orbitals.

So, does that mean the electron has equal chance of being found anywhere between the centre of the nucleus to the edge of the orbital?

Carmen_Sandiego said:

PM 2Ring said:

Oh good. :)

An electron in an s orbitals is a bit like a bungy jumper in space. The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.

The exact probability function describing the electron’s mean distance from the nucleus is fairly simple for the inner s electrons, but it gets more complicated for the higher s orbitals.

So, does that mean the electron has equal chance of being found anywhere between the centre of the nucleus to the edge of the orbital?

The Pauli Exclusion Principle forbids it being inside the nucleus I think :)

Stealth said:

The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.
—————————
That is such a cool analogy. I really like that, both for the concept it is trying to convey and the mental image of electrons tied into bungy harnesses.

:giggles: Thanks, Stealth!

Carmen_Sandiego said:

PM 2Ring said:

Oh good. :)

An electron in an s orbitals is a bit like a bungy jumper in space. The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.

The exact probability function describing the electron’s mean distance from the nucleus is fairly simple for the inner s electrons, but it gets more complicated for the higher s orbitals.

So, does that mean the electron has equal chance of being found anywhere between the centre of the nucleus to the edge of the orbital?

Definitely not! The probability that the electron is actually inside the nucleus is quite small (partly because the nucleus is so tiny compared to the mean distance), but QED says that it must be non-zero.

Here’s a graph for the first two s orbitals, the graphs of higher s orbitals have more peaks.

Dropbear said:

The Pauli Exclusion Principle forbids it being inside the nucleus I think :)

Nup. :)

PM 2Ring said:

Carmen_Sandiego said:

PM 2Ring said:

Oh good. :)

An electron in an s orbitals is a bit like a bungy jumper in space. The bungy cord is anchored to the nucleus, and the electron bounces back and forth at random angles, maintaining a uniform mean distance from the nucleus over time.

The exact probability function describing the electron’s mean distance from the nucleus is fairly simple for the inner s electrons, but it gets more complicated for the higher s orbitals.

So, does that mean the electron has equal chance of being found anywhere between the centre of the nucleus to the edge of the orbital?

Definitely not! The probability that the electron is actually inside the nucleus is quite small (partly because the nucleus is so tiny compared to the mean distance), but QED says that it must be non-zero.

OK, I just assumed the ‘non-zero’ part was due to the minuteness of the nucleus. Thanks. :)

Stealth said:

as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing
—————————
What is the scientific definition of “not bound gravitationally”?

Others have addressed this question, but I’d like to add that even under Newtonian physics it’s possible for two bodies to be not bound gravitationally even though the range of gravity is infinite. All it takes is for the two bodies to be separating with mutual kinetic energy greater than their mutual gravitational potential energy. This gives rise to the concept of escape velocity , which really should be called escape speed, but velocity sounds more scientific. :)

thanks PM for that explanation of models. hopefully everyone will be on the same page now.

PM 2Ring said:

Stealth said:

as time progresses the distance between the discrete masses that occupy the universe, but are not bound gravitationally (ie galaxies or collection of galaxies), is increasing
—————————
What is the scientific definition of “not bound gravitationally”?

Others have addressed this question, but I’d like to add that even under Newtonian physics it’s possible for two bodies to be not bound gravitationally even though the range of gravity is infinite. All it takes is for the two bodies to be separating with mutual kinetic energy greater than their mutual gravitational potential energy. This gives rise to the concept of escape velocity , which really should be called escape speed, but velocity sounds more scientific. :)

Thanks for giving some direction on that, PM :)

Boris said:

thanks PM for that explanation of models. hopefully everyone will be on the same page now.

We can but hope. :)