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ferrdek t1_jar0rcj wrote

Reply to comment by mfb- in Why do cosmologists say that gravity should "slow down" the expansion of the universe? by crazunggoy47

> matter slows down the expansion of the universe

I can't understand it. If large masses like stars etc cause stretching of space, why not assume that galaxies, clusters and filaments also stretch space between them, which would cause the expansion of the universe? Process of transforming energy into matter would fuel that expansion of space on a large scale.

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mfb- t1_jar92k5 wrote

> If large masses like stars etc cause stretching of space

That's a popular science analogy. Don't use it literally.

Every mass contributes to a slowing of the expansion, doesn't matter if we consider a proton, a star or a galaxy.

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ferrdek t1_jarayvg wrote

>That's a popular science analogy. Don't use it literally.

um, so what does it really means when scientists say that gravity warps the spacetime

>Albert Einstein proposed that massive objects warp and curve theuniverse, resulting in other objects moving on or orbiting along thosecurves—and that this is what we experience as gravity

https://www.science.org.au/curious/space-time/gravity

edit: what I'm saying if the bending of space we experience as gravity, we can experience simultaneous stretching of space as expansion

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mfb- t1_jarqhow wrote

It means spacetime is no longer the simple Minkowski space of special relativity. "Warped" does not mean "expanding". It's more of a local deformation.

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ferrdek t1_jarv0ep wrote

>"Warped" does not mean "expanding". It's more of a local deformation

Lets assume we have some point in space and we travel through it twice. First time the space is empty and the second time some massive object appear on our path (for instance a star) and we travel close to it, going through space warped by its gravity.

is the time needed to travel from point A to point B in warped space longer than time needed to travel that distance through unwarped space? Or the opposite? Or there is no difference?

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mfb- t1_jas94ee wrote

That depends on where A and B are and what your trajectory is in the case with the star.

> Lets assume we have some point in space and we travel through it twice.

If you consider travel from A to B then looking at a single point isn't sufficient.

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ferrdek t1_jasif3h wrote

>That depends on where A and B are and what your trajectory is in the case with the star

The star is located between A and B the trajectory goes through gravitational field of the star. Through space "warped" by the star.

By "point" I mean region of space. English is not my first language, sorry for misunderstandings

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