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70 votes

Are photons aged?

Photons can't have a perspective. If we have a particle with mass, we can imagine taking a frame of reference in which that particle is at rest. We can then see things "from the particle's ...
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53 votes
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Is Earth's Surface "In orbit"?

1. Is material on Earth's surface not in free fall around Earth's center? No. Material on the Earth's surface -- or inside it -- is not in orbit, and so is not in free fall. You can temporarily put ...
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46 votes
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Does the sun cross other spiral arms in its movement around the galaxy's center?

What is a spiral arm? The reason that the Sun, in principle (but see below), may cross spiral arms is that galactic spiral arms are not rigid entities consisting of some particular stars; rather they ...
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38 votes
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It takes light roughly 8 minutes to travel to Earth from the Sun, but based on which perspective?

If I interpreted this article correctly, then the answer to my question should be: 8 minutes is what we perceive, whereas for the photon the journey is instantaneous, due to the fact that it travels ...
33 votes
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How did Ole Christensen Romer measure the speed of light?

Ole Rømer did not measure a change in the frequency of light. He measured an apparent change in the orbital period of Io, one of Jupiter's moons. The orbit of Io can be measured very accurately by ...
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27 votes
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Exact measurement of a light year

By convention, astronomy uses the Julian Year for the computation of a light year: Although there are several different kinds of year, the IAU regards a year as a Julian year of 365.25 days (31....
23 votes

It takes light roughly 8 minutes to travel to Earth from the Sun, but based on which perspective?

When people talk about the time taken for light to go from the Sun to the Earth, they're generally just considering classical Newtonian mechanics, not relativity. So we simply divide the distance by ...
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20 votes
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Which star / galaxy is moving away from us the fastest?

When a galaxy recedes from us, the light we see from it is redshifted. For galaxies at cosmological distances, this redshift is fundamentally different from a Doppler shift; whereas the latter is due ...
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17 votes
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How precise are the observational measurements for the speed of gravity?

The accuracy is extremely good thanks to LIGO and a binary neutron star merger. It's accurate to about 3 parts in 1 quadrillion! See the paper Gravitational Waves and Gamma-rays from a Binary Neutron ...
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10 votes
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Is the ratio between earth's distance from the sun and the speed of light just a coincidence?

It is a co-incidence. The units are what you need to look at, in both the speed of light and the distance of the Sun the units of length are the same (m) (your ratio is $\approx 0.002 s^{-1}$ when you ...
9 votes

So where are these measurements of galaxies moving faster than light?

So where are these measurements of galaxies moving faster than light? They're redshift measurements. Check out the Wikipedia redshift article. It's good stuff. "we can actually observe galaxies ...
8 votes
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How fast is a comet moving when it crosses Earth's orbit?

Comets don't cross Earth's orbit really. Orbits are one-dimensional objects and their chance of crossing in 3D space is 0. Henceforth, I consider a comet at distance 1AU from the Sun. What's the ...
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8 votes

Regarding the age / size of the Universe

The expansion rate of space is not itself the reason that the radius $R_\mathrm{Uni}$ of the observable Universe is larger than 14 billion lightyears (Gly). Just the fact that space expands is the ...
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7 votes
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Does near light-speed travel doppler-shift the light from the target into gamma rays?

The equation for Doppler shifting towards the blue spectrum (i.e. when you are traveling towards it) is: $\lambda_b = \lambda_c/(c + v_b)$ where $\lambda_b$ is the shifted wavelength, $\lambda_c$ is ...
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7 votes
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Is Darkness Faster Than Light?

The darkness does not have a speed, as it's just the space the light travels through. It's always there until the brief instant a photon whizzes through. It would be analogous to asking what speed ...
7 votes

What is the Maximum Speed that can be acheived Because of Acceleration Due to Gravity?

It all depends on your frame of reference, but the biggest speeds caused by gravity will involve black holes or perhaps neutron stars. From the point of view of a far external observer, an infalling ...
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7 votes

Exact measurement of a light year

You're forgetting that one year is not 365 days, but 365.2422 or something close to that. That change will give you a number much much closer to the google provided number.
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7 votes
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Have more recent LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity further?

To get these kind of measurements one needs a gravitational wave detection with a electromagnetic counterpart. The big problem is, that the now quite common BH mergers are not expected to produce a ...
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6 votes

Are photons aged?

There is a quantity in relativity of $s^2$ which is defined as $t^2-x^2$, where $t$ is the difference in time between two events, and $x$ is the difference in position (measured in units such that $c=...
6 votes
Accepted

Absolute zero speed in space

The faster you move, the slower does time feel No. The faster someone else you are observing moves relative to you, the more time (as observed by you in their frame) slows down relative to the ...
6 votes
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Traversing a proton within the Planck time

If you don't like math: A fraction of a second. For math lovers: One proton is $8.414 \cdot 10^{-16}$ meters wide, and one Planck time is $5.391247 \cdot 10^{-44}$ seconds. This means that we are ...
5 votes

Is Darkness Faster Than Light?

Darkness is not a thing. It is just the absence of light. It doesn't have speed. Try observe the image: In this image this is shown that suppose there is darkness on any many light year far object if ...
5 votes
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Travelling at light speed(inside water)

Cherenkov radiation (Wikipedia) Cherenkov radiation, also known as Vavilov–Cherenkov radiation,[a] is electromagnetic radiation emitted when a charged particle (such as an electron) passes through ...
5 votes
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When stars explode why can we still see them?

Because we are not moving at the speed of light. From our point of view, light travels at the speed of light, and so events on a distant star are not visible until the light reaches us. From the ...
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5 votes
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How is it known that Pillars of Creation are destroyed?

Much of the evidence for the destruction of the Pillars of creation lies in observations of dust clouds in the region (Flagey et al. (2009)). The morphology and structure of a cloud in the dust are ...
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5 votes

Is there any way a meteor can hit at less than escape velocity?

Edited. No if you talk about the escape velocity form Earth. This follows simply from the fact that energy $E$ is conserved. An object that is not gravitationally bound to Earth has $E>0$ and hence ...
  • 5,306
5 votes

Is there any cosmological evidence that neutrinos travel at a speed other than c?

A paper by Wie et al. (2016) uses the coincidence between gamma rays from Gamma ray bursts and individual 3-30 TeV neutrinos to estimate the difference in propagation speed between neutrinos and ...
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5 votes

Is there any cosmological evidence that neutrinos travel at a speed other than c?

I can find plenty of evidence for electrons travelling at speeds less than c. The neutrino is said to be a fermion like an electron. But I can't find any evidence of neutrinos travelling at speeds ...
5 votes
Accepted

Does the edge of the Universe travel faster than the speed of light?

The universe has no edge, as far as we can tell. Now, the observable universe does have an "edge" - it's the most distant places we can see. But that's just us and our limited instruments. Due to ...

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