How big is the universe?

[Jokodo]

I disagree that the BB is without proof or demonstration. The cosmic background radiation and observed recession of distant bodies clearly demonstrates that expansion has occurred.

Mu response to that is correlation is not necessarily causation. You take 1000 data points and fit a curve to the points. The mathematical function fit tom the data is predictive , it will accurately predict results between measures data points. You can extrapolate past the endpoints.

I look at the BB as a sophisticated curve fit to a narrow set of observational data. The originating event is extrapolation.

There are conceptual problems for me. There was no center at the BB and there is now no center. However a speherical boundary of some kind implies a center.

And which part of the BB model implies a "spherical boundary of some kind"?

 

[James Chapman]

I disagree that the BB is without proof or demonstration. The cosmic background radiation and observed recession of distant bodies clearly demonstrates that expansion has occurred.

Mu response to that is correlation is not necessarily causation. You take 1000 data points and fit a curve to the points. The mathematical function fit tom the data is predictive , it will accurately predict results between measures data points. You can extrapolate past the endpoints.

I look at the BB as a sophisticated curve fit to a narrow set of observational data. The originating event is extrapolation.

There are conceptual problems for me. There was no center at the BB and there is now no center. However a speherical boundary of some kind implies a center.

And which part of the BB model implies a "spherical boundary of some kind"?

...Or any boundary at all, for that matter? As I understand it, a "finite but unbounded" topology is consistent with BB model.

 

[Jokodo]

And which part of the BB model implies a "spherical boundary of some kind"?

...Or any boundary at all, for that matter? As I understand it, a "finite but unbounded" topology is consistent with BB model.

Or indeed an infinite one. Finite but unbounded would appear to imply a curved spacetime, which we keep failing to detect.

 

[Sarpedon]

Mu response to that is correlation is not necessarily causation. You take 1000 data points and fit a curve to the points. The mathematical function fit tom the data is predictive , it will accurately predict results between measures data points. You can extrapolate past the endpoints.

I look at the BB as a sophisticated curve fit to a narrow set of observational data. The originating event is extrapolation.

There are conceptual problems for me. There was no center at the BB and there is now no center. However a speherical boundary of some kind implies a center. What led to the initial conditions?

Imagine a nuclear explosion. As the event progresses a civilization evolves on a particle from the explosion. Astronomers on the particle see everything moving away, an apparent expansion. They may deduce there was an originating cataclysmic event. They can deduce nothing outside of their limits of observation.

Your objections all rely on analogies to your earth-bound experiences. As cosmology, and indeed, science in general, become more advanced, they become further and further from our normal experiences. Thus, they all rely exclusively on mathematics. Analogies are useful, so long as you do not mistake the analogy for the thing so described. Yes, it is hard for us to imagine expansion without a center. No, that does not mean it can't occur. Your conceptual failings do not invalidate the model. That there is some dispute over what happened does not invalidate the model. There are a lot more data points than 1000, as you say. Mathematically, the certainty is quite high. The idea that the beginning was a cataclysmic event is just someone's analogy, a popular illustration of the model. Don't get hung up about it. The model has not quite reached the moment of origin, and does not have anything to say about the pre-existing states. This is not a problem with the model.

 

[steve_bank]

Mu response to that is correlation is not necessarily causation. You take 1000 data points and fit a curve to the points. The mathematical function fit tom the data is predictive , it will accurately predict results between measures data points. You can extrapolate past the endpoints.

I look at the BB as a sophisticated curve fit to a narrow set of observational data. The originating event is extrapolation.

There are conceptual problems for me. There was no center at the BB and there is now no center. However a speherical boundary of some kind implies a center. What led to the initial conditions?

Imagine a nuclear explosion. As the event progresses a civilization evolves on a particle from the explosion. Astronomers on the particle see everything moving away, an apparent expansion. They may deduce there was an originating cataclysmic event. They can deduce nothing outside of their limits of observation.

Your objections all rely on analogies to your earth-bound experiences. As cosmology, and indeed, science in general, become more advanced, they become further and further from our normal experiences. Thus, they all rely exclusively on mathematics. Analogies are useful, so long as you do not mistake the analogy for the thing so described. Yes, it is hard for us to imagine expansion without a center. No, that does not mean it can't occur. Your conceptual failings do not invalidate the model. That there is some dispute over what happened does not invalidate the model. There are a lot more data points than 1000, as you say. Mathematically, the certainty is quite high. The idea that the beginning was a cataclysmic event is just someone's analogy, a popular illustration of the model. Don't get hung up about it. The model has not quite reached the moment of origin, and does not have anything to say about the pre-existing states. This is not a problem with the model.

I have done a fair amount of data analysis and curve fitting.

How is the BB not an extrapolation beyond observed data points? However mathematically sophisticated, the BB is largely creative invention. Not that it is a bad thing, it is how new science starts. Creative invention and imagination.

Because the model leads to observed particles and cosmic structures from the hypothetical initial conditions does not mean the BB theoretical origins are true. There is no way to validate it.

IMO the question of size of the universe is meaningless. All we know is what we observe, and that is limed. The finite speed of light ensures there may be events we just can not see, at least yet.

Invoking Popper for something to be science it must be testable. Any prediction of size is not testable. This is why I say science, philosophy, and religion converge in cosmology.