Where? Please give a reference.BadgerBadger92 said:I hear some people say
It's impossible to tell without knowing the context, which means we need a specific reference.BadgerBadger92 said:What exactly do they mean by this?
Well my “source” isn’t reliable, it was Facebook where people were telling me space is flat, which I never heard before so I decided to ask you guys for a clear answer. Luckily I’m starting school at a local community college.PeterDonis said:Where? Please give a reference.
It's impossible to tell without knowing the context, which means we need a specific reference.
For one thing, since you posted this in the relativity forum, "space" is not the same as "spacetime", and "space" being flat is something different from spacetime being flat.
As a general matter, "flat" when referring to a metric space means that the Riemann curvature tensor derived from the metric is zero.
Be aware that “space is flat” and “spacetime is flat” are different things.BadgerBadger92 said:TL;DR Summary: I’ve heard a lot of people that say this
Please excuse my ignorance
I hear some people say that space is flat. What exactly do they mean by this?
The problem here is lack of context. Who are those people (professors, students, some random blokes?)and what were they talking about (cosmology, maths, undergrad physics homework?)? And are you sure they said space and not spacetime?BadgerBadger92 said:I hear some people say that space is flat. What exactly do they mean by this?
Note that this isn't true (at least, not without caveats) in the "space is flat" cosmological solution, because spacetime is not flat (nor empty). This kind of thing is why context is important, @BadgerBadger92.Hornbein said:It means that if you send out two parallel laser beams through empty space they will stay parallel forever. They won't converge or diverge. Maybe it would have been better to call this straight space.
Which, as you admit, is not a good source. And certainly does not provide any kind of useful context.BadgerBadger92 said:my “source” isn’t reliable, it was Facebook
When people say "space is flat," they are referring to the geometric properties of the universe on a large scale. In a flat universe, the rules of Euclidean geometry apply, meaning parallel lines never converge or diverge, and the angles of a triangle add up to 180 degrees. This concept is rooted in the theory of general relativity and the overall shape of the universe.
Scientists determine the flatness of space by studying the cosmic microwave background (CMB) radiation, which is the afterglow of the Big Bang. Measurements from satellites like the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck satellite have shown that the universe is very close to flat, with only a very small margin of error. These observations are consistent with predictions from the inflationary model of the universe.
A flat universe implies that the universe will continue to expand forever, but at a rate that slows down over time. It also has implications for the total amount of matter and energy in the universe, suggesting that the density of the universe is exactly equal to the critical density needed for a flat geometry. This has significant consequences for cosmological models and our understanding of the universe's fate.
Yes, space can be curved in two other ways: it can be positively curved (like the surface of a sphere) or negatively curved (like a saddle). In a positively curved universe, parallel lines eventually converge, and the angles of a triangle add up to more than 180 degrees. In a negatively curved universe, parallel lines diverge, and the angles of a triangle add up to less than 180 degrees. Current observations suggest that our universe is flat or very close to flat.
Dark energy is a mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion. The presence of dark energy affects the overall geometry of the universe. For the universe to be flat, the contributions of dark energy, dark matter, and ordinary matter must balance out to achieve the critical density. Dark energy's properties and its role in the expansion of the universe are still active areas of research in cosmology.