Curvature of space and dark matter

[moronthat]

Assuming gravity is matter curving space as Einstein says, isn't our theory of dark matter just an assumption that because more gravity is required to explain galaxy formation that it must be caused by unseen matter? Why do we assume that the curvature of space required must be caused by matter?

Another question, using a slinky as an analogy. Everyone is familiar with stretching one and observing traveling pressure waves along it. Those pressure waves are like space curvatures caused by mass. But in a slinky the high pressure waves are also accompanied by low pressure waves to compensate, sort of an equal and opposite reaction. Has anyone ever thought that the curvature of space caused by gravity has a similar effect of less curved space near it to compensate? If that's true, wouldn't that act like dark energy?

 

[Ich]

Why do we assume that the curvature of space required must be caused by matter?

There is a Wikipedia article with 3570 words on observational evidence. If you don't understand something in it, maybe you could ask a specific question?

Has anyone ever thought that the curvature of space caused by gravity has a similar effect of less curved space near it to compensate?

Sounds like gravitational waves. But these are a bit more complicated than pressure waves.

 

[phyzguy]

We know that all matter causes a gravitational pull, as described by Newton's law of gravity. Many observations tell us that there is more gravitational pull out there than can be ascribed to ordinary matter. Whatever is causing the extra gravity is "matter", almost by definition. Since we don't know what it is, and it doesn't emit light, we call it "dark matter". What else would you like to call it?

 

[rwmp]

I graduated more decades ago than I like to admit but I got curious and after some research I am blocked by these questions. It seems like the whole evidence for our universe expansion accelerating is that photons which travel a very long space time path arrive with less energy than expected (more red shift and less luminosity). We can detect no direction which seems to point to the center or edge of the universe. If I frame this problem in 2 dimensions I find this only matches objects all on the surface of an expanding sphere. Is there a 3-D analog where all visible objects are on the surface of an expanding extra dimensional sphere? Is this ruled out due to evidence I can't find through reviewing information on the web? There are a number of searches going on for a graviton. If there was a force mediating bosun wouldn't it be captured within a black hole and cause a black hole to not have any gravitational effect outside of its event horizon?

 

[sardar]

I can understand the confusion and questions surrounding the concepts of curvature of space and dark matter. These are complex and still not fully understood phenomena in the field of astrophysics. However, I would like to clarify some points and provide a response to the content.

Firstly, the theory of general relativity proposed by Einstein states that matter and energy can curve the fabric of space-time, and this curvature is what we experience as gravity. This has been extensively tested and has been shown to accurately predict the behavior of objects in the universe. So, it is not just an assumption but a well-supported and tested theory.

Secondly, the existence of dark matter is not just based on the need for more gravity to explain galaxy formation. There are various observations, such as the rotation curves of galaxies and gravitational lensing, that point towards the presence of a large amount of unseen matter in the universe. In fact, the amount of dark matter needed to explain these observations far exceeds the amount of visible matter in the universe. So, it is not just a matter of assuming, but rather a conclusion drawn from multiple lines of evidence.

Regarding the analogy of the slinky, it is important to note that the concept of curvature of space is not the same as the physical wave-like motion of a slinky. The curvature of space is a mathematical concept that describes the bending of space-time due to the presence of matter and energy. While it is true that the presence of matter can create a curvature in space, it is not accompanied by a compensating "anti-curved" space. This is because space is not a physical object that can be "stretched" or "compressed" like a slinky. It is simply a mathematical construct used to describe the fabric of the universe.

Finally, the concept of dark energy is a separate phenomenon from dark matter. Dark energy is thought to be responsible for the accelerating expansion of the universe, and its existence is supported by various observational data. While there are some theories that attempt to explain dark energy as a result of the curvature of space, it is still a highly debated and ongoing area of research.

In conclusion, the concepts of curvature of space and dark matter are not just assumptions, but rather well-supported theories based on observational evidence. While there may be some analogies and connections between these concepts and physical phenomena, it is important to understand that they are distinct and cannot be directly compared. As scientists, we continue to explore and study these