# Questions tagged [distance]

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### Formula for blurring out a grid of holes

Place a camera lens with focal length f_l mm and camera sensor size w mm and h mm behind an ...
7answers
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### Why isn't the GPS location calculated from the Schwarzschild metric?

The GPS uses the flat space light propagation formula to calculate the distance from the source (the satellite) to the receiver (observer on Earth): $$d=c \cdot \Delta t$$ where $c$ is the speed of ...
3answers
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### Can length contraction help the moving observer reach a star system 'faster'? [duplicate]

Would an observer moving with close to the speed of light ($\sim 99\%$) towards a star system that's $20$ light years away perceive the distance as being less than $20$ light-years? If yes, how much ...
1answer
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### Calculating the distance between two masses with respect to gravitational force [duplicate]

Call them $m_1,m_2$. They are compressed to their center of masses, if you wish. If the initial distance at $t=0$ is $d$, is there a formula or an efficient way to calculate the distance between them ...
4answers
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### Are any of Euclid's 5 postulates false in Minkowski spacetime?

I often hear that Minkowski spacetime is non-euclidean. Euclidean geometry is characterized by Euclid's five postulates being true. Which of those postulates are untrue in Minkowski spacetime (if any),...
4answers
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### Why is Work equal to Force * distance? [duplicate]

I totally get the mathematical part, but I cannot imagine how this works. I apply a force to a ball. Why does the distance over which it moves matter to me? Sure, if I calculate the kinetic Energy of ...
1answer
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### Shortening of distances in Relativity Theory

I am studying relativity theory and I have understood why distances become shorter from the perspective of someone who is travelling close to the speed of light. However, later on I read that the ...
1answer
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### Compare 2d metric to metric on sphere-puzzling result

I calculated the infinitisimal distance squared $(\mathrm{d}s)^2$ in 3d polar coordinates and 3d cartesian coordinates in an example to show that they were identical. I chose $P(r,\theta,\phi)$ as ...
2answers
87 views

### Are distance and displacement always frame independent?

I'm aware that distance and displacement, both are independent of reference frames, when the two frames are stationary wrt each other. Because the actual distance (or the shortest distance) between ...
2answers
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In quantum information, we frequently use the trace distance (see definition) to look at how similar two states are. If I had a known complete set of states $\{\rho_i\}$ and some unknown state $\... 2answers 58 views ### Can we determine the distance from a radio station (antenna) and a receiver using radio wave ? say we have the a receiver and radio antenna can we calculate the distance between the receiver and the antenna by a receiver if we know the frequency ? 1answer 65 views ### How loud would a sound have to be for it to travel the distance of Pittsburgh, Pennsylvania to New York, NY? [closed] I'm just wondering if it's possible, more than anything. But if it is, how many decibels would the sound have to be to travel that far of a distance? 2answers 4k views ### How far can a shout travel? I was wondering, if a person climbs a tower and shouts at the top of his lungs how much distance would the sound travel ? Would it reach someone 1km far? Assuming that there are no tall buildings in ... 1answer 84 views ### How much energy needed to cross the galaxy in time$t$? Sorry if this is a dumb question. A friend of mine just asserted that it's possible to get anywhere in the universe in less than 30 seconds of your time due to time dilation. I do imagine that'll ... 0answers 78 views ### How far are we from the “edge” of the universe? [duplicate] According the the Big Bang theory, the universe started as a 0-dimensional point of infinite density. Shortly thereafter, it underwent inflation and grew to some measurable size, and continues growing ... 1answer 56 views ### How accurately can the distance of a star be measured? With the launch of the GAIA mission some years ago, a new precedent was set in mankind's ability to map our universe. However, how accurate are the distances created by this? From ESA's website, I ... 1answer 474 views ### Calculate distance an accelerometer moved I am reading accelerometer data and want to determine the distance that the accelerometer is moved. ( My question is similar to the one placed here, Calculate speed from accelerometer . I just feel as ... 0answers 71 views ### Is there a difference between horizon and comoving distances? I wonder if there a difference between horizon and comoving distances in cosmology ? I mean both correspond to a null geodesic$(ds^2=0)$right ? 1answer 106 views ### The distance of an object undergoing constant acceleration Is the distance an object moving increases with time if it is accelerated with a constant rate? I mean, doesn't it depend on the direction the object is traveling? if I throw an object upward, ... 1answer 43 views ### Galactic Distances I'm trying to show: 1 arcsec on the sky is approximately 5d parsecs at a galaxy, d parsecs away Could someone show me a proof of this statement, because it is bamboozling me! 1answer 2k views ### The difference between comoving and proper distances in defining the observable universe "The radius of the observable universe is estimated to be about 46.5 Gly." If I understand correctly, it means the most distant object that we can see right now is 46.5 Gly away (at present), but it ... 8answers 4k views ### Does the mass of a bicycle directly affect stopping distance? In this answer on the cycling SE, the claim is made that adding more mass to a bicycle increases the stopping distance. I was under the impression that mass should not affect the stopping distance so ... 1answer 1k views ### Inverse square rule for strong forces Most of the forces induced by a point particle follows the$1/r^2$rule. Then why does the strong force not obey it? 1answer 47 views ### Why are distances in cosmology larger with$\Lambda\$?

I'm starting to study cosmology on these beautiful notes: http://www.damtp.cam.ac.uk/user/db275/Cosmology/Lectures.pdf . At page 16, when talking about distances in cosmology, the author says that ...