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7

Gravity doesn't affect the speed of light. It affects the space-time geometry and hence the paths of light. However, this can have a similar effect. Light emitted at source $S$ to pass a massive object $M$ that is very close on the otherwise (if M weren't there) straight path to an observer $O$ has to "go around" $M$, which takes longer than following the ...


7

This has been considered long ago (Here's a paper talking about this). Wormholes are not forbidden by physics, but the creation of wormholes is iffy ground. THere are two possible paths one can take to create a wormhole: Choose a pre-existing wormhole in the quantum foam and "expand" it by feeding it exotic matter. "Tear and sew up" space — we're ...


6

Stellar clusters around supermassive black holes are systems in which relativity likely plays a role. Currently, only bright stars can be seen in our own galactic center because there is a ton of neutral gas between us and the galactic center that obscures it. As a result, we only have a few "test particles" out of the many stars that actually orbit the ...


5

My topological defect cosmology is a little rusty, but I'm pretty sure this is how it goes. Start with the fluid equation, $$ \dot{\rho} + 3 {\dot{a} \over a} \left( \rho + p \right) = 0, $$ and the equation of state, $$ p = w \rho. $$ Plug the equation of state into the fluid equation, assume a constant $w$, and you'll find $$ \rho \propto a^{-3(1 + w)}. $$ ...


5

As Walter says, gravity doesn't bend light. Light travels along null geodesics, a particular type of straight path. Since (affine) geodesics don't change direction by definition, geometrically light trajectories are straight. Moreover, the speed of light in vacuum is $c$ in every inertial frame, regardless of whether or not spacetime is curved, although a ...


4

Newtonian gravity of a point-source can described by a potential $\Phi = -\mu/r$. If we suppress one spatial dimension and use it to graph the value of this potential instead, we get something that looks very close to this illustration, and is indeed infinitely deep at the center--at least, in the idealization of a point-mass. And farther away from the ...


4

I will make a small calculation here, but please proceed to the results if you may like to. Calculation Stars are spherical and static, so metric near their surface (photosphere) and outside on is Schwarzschild. Hence time-time metric component on the surface is: $$g_{44}=1-\dfrac{R_{grav,*}}{R_*}$$, where $R_*$ is the radius of the star and $R_{grav,*}$ ...


4

You have many questions. I only answer the first. It's doesn't only matter how heavy a star is, but also how big. For ordinary stars, the effect is neglible (work it out by yourself -- it's a useful exercise). Even for compact stars, such as white dwarves or neutron stars, the effect is small. However, what astronomers commonly refer to as (stellar-mass) ...


4

I think the image you posted is not quite reallistic. On it, objects are just inverted from some radius on, while what you can expect from a real black hole seen from near enough is a combination of these: a) an accretion disc b) a companion being sucked c) Hawking's radiation d) X-Ray burst from the poles (really starting out of the event horizon) You ...


3

Since the astronomers are using radio telescopes and not optical telescopes, I'd like to point out why they are doing so - The centre of the Milky Way is a very dusty place. Wavelengths from the millimeter to optical get easily absorbed by all this dust, so it's very difficult to see the centre of the galaxy in the optical spectrum. But radio waves do not ...


3

That's a lot of not quite trivial questions! I'll try to answer part of it. First, the red-shift can be composed of relativistic Doppler-effect and gravitational red-shift. When neglecting the gravitationl part, we get a higher radial velocity. The radial velocity can be used to calculate a distance estimate via the Hubble "constant". So for low velocities ...


3

Let's restrict to special relativity, meaning two inertial frames moving in a Minkowski spacetime. A clock in the first inertial frame ticks slower, when seen from the second. A clock in the second inertial frames ticks slower, when seen from the first. Now assume, that you are fixed to one of the two inertial frames. Usually you measure velocities within ...


2

At 99% the speed of light the behaviour would be almost completely determined by special relativity. The scenario is well-investigated for synchrotrons. In principle a synchrotron or a storage ring, e.g. around the equator of Earth, could be built. At 99% the speed of light the frequency $f_s$ of the circling object should occur red-shifted by a factor of a ...


2

Without some reference to compare to, time passing more slowly makes no sense at all. But every clock has its own proper time that measures time along its own worldline. In cosmological models, the cosmological time is the proper time of a certain kind of ideal observer: one comoving with the Hubble flow. In other words, imagine space filled with observers ...


2

Gravity is sometimes described as a curvature in space-time. Due to relativity, doesn't this imply that gravity doesn't propagate? There's a fairly precise sense in which gravity propagates: if you have a spacetime and you perturb it a bit, then you can think of the new spacetime as the old "background" spacetime with a small change on top of it. Then ...


2

Black holes distort the geometry of spacetime. So you need to take care about that. Changes of gravity propagate with the speed of light. That's thought to occur for accelerated mass, e.g. a binary of black holes. A second fundamental point: Speeds don't add up in an additive way, but in a subadditive way: speed of light + speed of light = speed of light. ...


2

Adding to @Guillochon's answer, there are even a number of general relativistic tests in our solar system, the most famous being the precession of the perihelion of Mercury. In short, the location of the point of closest approach to the Sun (perihelion) for the planet Mercury is a changing quantity. Essentially, given one full revolution, it doesn't trace ...



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