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denism
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I read that the radius of the universe is around 1.3x10^26 meters but I did not find how this size has been calculated.
Thanks if you can explain to me
Thanks if you can explain to me
denism said:if you prefer: What are the tools used by reputable sources to estimate the minimum radius of universe?
denism said:My question was about the total size, or more precisely: do we have (indirect) evidences that there is really something beyond the Hubble sphere (of radius c/H)
denism said:In fact, this belief is only based on the assumption that recessional velocities can exceed light speed but I never saw any observational support to this postulate
And you say this why? Because wikipedia hasn't presented you with any? It would be wise to delve deeper before making such sweeping, contrarian statements.denism said:I am afraid that there is not a single supporting observation in this story
denism said:Yes. But precisely, all what I read about universe expansion and horizons, begins with a redefinition of the line element of SR (ds2=(cdt)2+a(t)2dl2)
denism said:I would be very pleased seeing any supporting data!
I did not want to be contrarian. Considering my poor knowledge in this field, I am sure that data (more convincing than the theoretical extension of Vrec = HD) should exist. This was precisely the purpose of my question
qraal said:An infinite flat space-time is just the simplest topology to assume. .
"Flat" means Euclidean 3D. It need not be infinite.denism said:does "infinite flat" means euclidean 3D?
denism said:But how do you conceive a finite euclidean 3D space? with a peripheral boundary? looks strange
A torus.qraal said:That requires some tricky topology I'm guessing :-)
You can think of it that way, yes. The best way to visualize it, though, is as a cube with opposite faces identified (by identified, I mean topologically connected -- for example, a circle is a line segment with the end points identified.)denism said:4D torus?
denism said:Indeed I was not clear. I just wanted to say that authors talking about light connection rates in the expanding universe never make use of GR, but only derive their conclusions from the simple relationship cdt=a(t)*dl (note there is a typing error of sign in my previous equation).
denism said:SR seems to be sufficient. Gravity and GR are generally not involved in the universe model used in these studies.
denism said:Furthermore, even SR seems to be not observed: calculations using speed substractions such as c-Vrec, rather resemble to classical mechanics ... even if I understood that Vrec is not a genuine speed.
George Jones said:[itex]ds^2 = 0[/itex] for a lightlike worldline in both special and general relativity.
George Jones said:This is just plain wrong. In order to use the equation in your post above, the dependence of [itex]a\left(t\right)[/itex] on [itex]t[/itex] is needed. This is given by the solution of the differential equation
[tex]
\left( \frac{da}{dt} \left(t\right) \right)^2 = H_0^2 \left( \Omega_{m0} a\left(t\right)^{-1} + \Omega_{r0} a\left(t\right)^{-2} + \Omega_{\Lambda 0} a\left(t\right)^2 + 1 - \Omega_{m0} - \Omega_{r0} - \Omega_{\Lambda 0} \right),
[/tex]
where the constants [itex]\Omega_{m0}[/itex], [itex]\Omega_{r0}[/itex], [itex]\Omega_{\Lambda 0}[/itex] are the current densities (relative to critical density) of matter, radiation, and dark energy, respectively. This equation comes from Einstein's equation of general relativity, i.e., it come form Einstein's theory of gravity.
George Jones said:With appropriate definitions of time and distance, c - V_rec is true in special relativity, and in the FRW cosmological models of general relativity
Scientists use a variety of methods to calculate the size of the universe, including measuring the cosmic microwave background radiation, observing the expansion rate of the universe, and using mathematical models based on the laws of physics.
The estimated size of the observable universe is approximately 93 billion light-years in diameter. This is based on the most recent measurements of the expansion rate of the universe and the age of the universe.
Due to the vastness of the universe and the limitations of our technology, it is unlikely that we will ever know the exact size of the universe. However, scientists continue to refine their methods and make new discoveries that help us better understand the size and structure of the universe.
The size of the observable universe is a small fraction of the total size of the universe. It is believed that the universe is much larger than what we can observe, and it may even be infinite.
Calculating the size of the universe allows us to better understand the nature of our universe and our place within it. It also helps us make predictions about the future of the universe and provides valuable insights into the laws of physics and the fundamental forces that govern our universe.