Geography, 02.08.2019 12:00 Mathewcastillo88

Three galaxies are aligned along an axis in order a, b, c. an observer in galaxy b is in the middle and observes that galaxies a and c are moving in opposite directions away from him, both with speeds 0.63c. what are the speeds of galaxies b and c as observed by someone in galaxy a?

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This is a somewhat tricky question. Our universe is constantly expanding. Ignoring small gravitational effects, if we are centered at a galaxy and look around us, every other galaxy should be moving away from us. Nevertheless, there is no central point in our expansion. Imagine dots on a balloon; as we blow the balloon, all points distance themselves from the others, with no point being central. The speed of this "expansion" is given by Hubble's law: u=H*d where u is the speed with which a galaxy is moving away from us, d is our distance to that galaxy and H a univeral constant, Hubble's constant. This helps us with the first question; A will see B recede with an equal speed from it, 0,63c. We have from the geometry of the situation that $d_{AB} + d_{BC} =d_{AC}$ . $u_{AC} =H* d_{AC}$ also holds. Now, substituting in our distance equation and using Hubble's law, we get that $u_{AC}=u_{AB}+u_{BC}=1.26c$ . Thus, A will see galaxy C receding at a speed of 1.26c. This is not against the theory of relativity, but it is a very mathematical point; do not worry about your speed being higher than the speed of light!

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helen told me that she hoped i had enjoyed myself.

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it is very hard for the climatologists to precisely predict how will the global temperatures be changing so there's lots of models, some of which differ significantly, this is due to multiple factors, and probably the most important is the human activity.

humans have been a key factor in climate change around the globe since the start of the industrial revolution, and in the past few decades the consequences are becoming more obvious. there's lots of emission of pollutants in the atmosphere as well as changing the environment on the surface itself, so it's really hard to predict how will that go in the future because there's some countries that are reducing the damage and are going towards green energy, while others are stubbornly continuing with pollution and damages to the environment.

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Three galaxies are aligned along an axis in order a, b, c. an observer in galaxy b is in the middle...