26

General relativity predicts that there are only two possible polarizations of gravitational waves, the so-called "tensor" polarizations $+$ and $\times$. It turns out you can show that the tensor polarizations actually don't lead to time dilation, making any attempted measurement of it pointless. The short answer, then, is that we don't expect to ...


25

Not at all a dumb question. As you have heard, it is true that time is affected by gravity. The stronger the gravitational field, the slower time passes. If you're far from any gravitating matter, time passes "normally". But to answer your question, we must specify what is meant by "the black holes's time" (let's call the black hole $\mathrm{BH}_\mathrm{Sgr\...


8

Jonathan's answer is essentially correct, but as Rob Jeffries comments, he doesn't take into account that the Universe is expanding during the journey. The edge of the observable Universe is 47 billion lightyears (Gly) away. Even if you are a lightbeam, you cannot reach that point. The farthest you can go if departing today is roughly 5 Gpc, or 17 Gly, but ...


8

Pretty much every hydrogen atom that's in a glass of water has a proton that dates from 1 / 1000000 seconds after the big bang. That's older than the cosmic microwave background, which dates from almost 400,000 years later.


8

Suppose there was a magic gun that fired a bullet at ten times the speed of light relative to the firer. If I have the only such gun, and I don't move then there is no paradox. But now suppose these guns are generally available. At time zero, an observer flies past me at velocity 0.5 c and I give them one of these guns. 7 years later, I fire the gun ...


7

If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. Yes, no problem with the gravitational time dilation. However, what if we sent a probe with a camera to a black hole? When we watch the screen, would we see time through the camera's perspective — that is, would the Universe appear to ...


7

If it has to do something with gravity affecting the inner working of wind up and pendulum clock will this also affect digital clock ? As astrosnapper noted in his comment, gravitational time dilation affects all time-dependent processes. This includes not only clocks (including digital clocks and atomic clocks), but also the rates at which chemical ...


7

I'm going to give a longer, slightly less accurate answer because this is a fun question. I'll start with special relativity because it's easier to understand. Using a thought experiment the velocity and time dilation relation is not that hard to see and to calculate it, just use Pythagoras. A photon bouncing between two mirrors can be used as a kind of ...


7

You are essentially asking the following: if someone falls from the Earth from some way beyond the event horizon of a black hole, how long after they have left can an observer on Earth still signal to them with a light beam? The answer of course depends on exactly how far the Earth is from the black hole. It is also often forgotten that it is not just light ...


7

The answer by @HDE 226868 addresses the current attempts by LIGO/Virgo and PTAs to detect alternate gravitational wave (GW) polarization states, which have not been detected. In that answer, this SE question is cited, which shows that gravitational waves being interpreted as tensor perturbations of the flat (Minkowski) spacetime produces only two non-trivial ...


6

Models are uncertain I'm guessing that you are referring to age estimates of very old stars. The age of a star can be determined from certain observables, among one is its absolute luminosity, which in turn requires a precise measurement of its distance. Even today, the uncertainties involved yield estimates with mean values longer than the age of the ...


6

The reason we think that the cosmological redshift is caused by the metric expansion of space is 1) that there is a well-known, physical mechanism that can cause this effect, and 2) that this mechanism is a prediction of a well-established and thoroughly tested theory, namely the theory of general relativity. The physical mechanism in question can be ...


6

Yes, but not very likely. The closest orbit that does not require constant expenditure of energy to maintain it is the prograde equatorial ISCO. For a Kerr black hole the time dilation factor on this orbit is $$\frac{dt}{d\tau}\approx \frac{2^{4/3}}{\sqrt{3}(1-a/M)^{1/3}},$$ which at the astrophysically likely Thorne limit $a = 0.998M$ gives a dilation of ...


5

A typical neutron star of $1.5M_{\odot}$ is thought to have a radius of around 8-10 km. This is only a factor of 2 larger than the Schwarzschild radius for a similar mass black hole. We know that more massive neutron stars do exist. The current record holder is around $2M_{\odot}$. Most equations of state (the adopted relationship between pressure and ...


5

It doesn't have to be a visible telescope, any electromagnetic radiation will act in the same way. I'll give you the answer, but if you want the details you need to look at a description of the resolution to the so-called twin paradox, for for example here. Assume that the spaceship travels outwards and back to Earth at the same speed, with a brief ...


5

In the comments of the other answer, the question came up whether decay of the orbit would limit the time amount of time dilation. The answer is of course yes. But by how much? This question can be answered using some modern results for the modelling extreme mass -ratio binaries in the limit of extremal spins. The answer will depend crucially on ratio of ...


5

A physics professor once described the following exchange, and I found it immensely helpful. It's not an exact answer, but the formatting requires an answer post. Question: What is time? Answer: (hover your cursor to reveal) In the context of this question this means that whatever effect you are considering it is an effect on time, not on the clock. ...


4

For simplicity, let's say that the black hole is isolated and non-rotating (and uncharged), so that the situation is described by the comparatively simple Schwarzschild spacetime. Let's also suppose that the camera free-falls radially into the black hole. What is the camera looking at? Suppose it is looking at some stationary object that does something with ...


4

The way that you have specified the question, the answer is as far as you like. You simply put your spaceship into any orbit around the black hole and wait. A more sensible question is what is the largest time dilation factor that can be accomplished - i.e. that maximises your travel time into the future for a given amount of proper time experienced on the ...


4

If we could detect the cosmic neutrino background, then I would class those neutrinos as "things" and there should be lots of them! I guess whether they are detected or not, they are extremely likely to be there. These cosmic background neutrinos were produced when the universe was about 1 second old. I agree that most protons are almost a second older! ...


4

The point of the unification of space and time in relativity is that there's no sense in asking what's happening "right now" at a different position. It makes as much sense as asking what's happening "right $y$" at a different $x$ in Euclidean geometry. If you fix a Cartesian coordinate system then "right $y$" is mathematically ...


3

Remember this is a theory of "relativity". Now, time dilation due to gravitation effects is rather outside our normal experience. But there are relativistic effects that that you experience all the time. I'm sitting on a train. Relative to my computer I'm not moving. Relative to the track I'm travelling at 100km/h. Relative to the sun I'm moving about 30 km/...


3

Trajectories close to a black hole can't be approximated by Newtonian mechanics, General Relativity is needed. The black hole doesn't have a surface, but the Schwarzschild radius is point of no return. However it is not possible to orbit just above the Schwartzchild radius. If you are less than 1.5 radii from the event horizon, there are no orbits. The ...


3

Yes. And we are actively searching for these systems, e.g., with the Pulsar timing array and "soon" with instruments like SKA. From the Astro2020 Science White Paper on Fundamental Physics with Radio Millisecond Pulsars: A broad class of alternative theories invoke mediation of gravity through both tensor and scalar fields, whereas general relativity ...


3

Einstein's general theory of relativity explains time dilation. Wikipedia provides a concise summary: time dilation is a difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field. As a result of the nature of spacetime, a ...


3

Your question is difficult to answer exactly, because it touches the question of consciousness, which is problematic in general. But the answer is basically this: Theory of relativity describes the space-time as four-dimensional space that exists as a whole. You are described by a world-line, which contains all states you go through from birth to death. ...


3

My question is to know if will you "live for a thousand years" (...) or "only" 10 years in your spaceship - time "froze" during the travel. If you were to travel to close the speed of light (not doing the math, plainly speaking), you would appear to live for a thousand years to the people that are outside of your frame of reference. Time would actually pass ...


3

a Gravitational-Time dilated place to somewhere far which is not dilated "Dilated" or "not dilated" are not absolutes. It's always a relative thing. "Dilated" relative to me, but perhaps "not dilated" relative to you. There is no dilation that happens "in general"; it's always relative to another place/observer/reference. Would those people look fast ...


3

The formula is given on wikipedia $$t_{0}=t_{f}{\sqrt {1-{\frac {2GM}{rc^{2}}}}}=t_{f}{\sqrt {1-{\frac {r_{s}}{r}}}}$$ Here $t_0$ is the time measured by clock distance $r$ from an object whose Schwarzschild radius is $r_s$ as calculated by a distant observer at rest whose clock measures $t_f$. This is however, dependent on how the distant observer ...


3

No. Time dilation is expected and observed as a result of universal expansion (e.g. in the light curves of type Ia supernovae and the duration of gamma ray bursts, Blondin et al. 2008; Zhang et al. 2013). There is no way of distinguishing between a Doppler shift and cosmological redshift for an individual source.


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