Recent content by dougy

What would be interesting to know is whether that microarcsecond resolution applies to high-redshift galaxies. The resolution achieved in the paper you linked seems to be on the order of 0.1 arcsecond. Also we would still need to determine how that angular resolution translates to a speed of...

How precise is this fit to the speed of light? What's the margin of error and how far would be the most distant galaxies tested in this way? To test whether a part of the redshift of distant galaxies might be due to their light traveling slower when it reaches us. I know it sounds crazy from...

Usually we measure the speed of light using light generated here on Earth or coming from the Sun or other stars, but have we ever tried to measure the speed of the light coming from distant galaxies? As in directing that light into an apparatus and measure its average velocity over a round-trip...

Well it is not necessary to invoke spacetime to derive the predictions of special relativity, the Minkowski framework was introduced after Einstein's original formulation. The predictions of general relativity follow from the equivalence principle, special relativity and some other assumptions...

The cosmological principle is a statement that the universe appears the same to all observers, you can't infer the homogeneity of the universe from one sole vantage point without additional assumptions. Sure special relativity doesn't hold in the FLRW metric, which assumes homogeneity. My...

This is wrong. Consider v(D) = c*tanh(HD/c). Assuming the constancy of the speed of light the relativistic addition of velocities holds, then you can check that (v(D+d)-v(D))/(1-v(D)v(D+d)/c²) = v(d), and the cosmological principle is obeyed. You may want to argue that the constancy of the speed...

That's precisely the core of my question: why does the fact a universe expands slowly enough that the gravitational attraction eventually takes over imply that this universe is spherical? Where would be the contradiction in a spherical universe where galaxies are moving too fast for the...

Wouldn't a universe where recession velocities are the same function of distance for each observer (i.e. not necessarily proportional) obey the cosmological principle too? I wouldn't say fundamentally impossible, I'm sure it could be done but it would take much longer and in the end the...

In the absence of a cosmological constant, there is a critical density (in the FLRW model) at which the universe expands asymptotically to zero velocity. If the density of the universe (without a cosmological constant) is above that critical density, at some point the expansion reverses and...

If you never passed me but were always moving away from me you couldn't do that experiment with the apple. With your interpretation it seems you would say there is no momentum involved between two objects that never meet, and so with your interpretation that I couldn't measure the velocity of...

"Things are just getting farther apart", which means they have a relative velocity. Unless you are treating space as an entity that expands between galaxies while galaxies remain at rest relative to that space, which is the fallacy of reification. On the scale of the observable universe...

The problem is it stops being just "philosophy" when statements such as "galaxies move away from each other because space expands" or "light is redshifted because of the stretching of space" are given unscrupulously everywhere. If space is a mathematical framework then it is false to state that...

I'll quote Carl Sagan, talking about a photograph of Earth taken from 6 billion km away (the Pale Blue Dot): " Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their...

Why do we enjoy certain things? Well there isn't always a rational reason, sometimes we just do, that's how we are wired. But if there is no rational reason in your case, maybe you're scared that one day you will stop enjoying it. Some people never ask themselves the question, others need a...

Does this effect really matter when D remains in a constant gravitational potential? Even though the distance between D and the other observers changes the light signal still has to cross the same difference in potentials. Intuitively I'm thinking that if a light ray travels twice the distance...