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71 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 ...
James K's user avatar
  • 123k
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 ...
Peter Erwin's user avatar
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47 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 ...
pela's user avatar
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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 ...
Rob Dirnens's user avatar
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 ...
James K's user avatar
  • 123k
29 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 (31.5576 ...
Toby Speight's user avatar
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 ...
Barmar's user avatar
  • 975
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 ...
pela's user avatar
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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 ...
Zamicol's user avatar
  • 1,005
15 votes
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Why speed of light is considered to be the fastest?

The recession rates relevant to Hubble's law are not relative velocities, so there's no reason to compare them to the speed of light. They can be defined as follows. Conceptually, imagine a chain of ...
Sten's user avatar
  • 4,694
11 votes

Why do we say that gravitational waves travel at the speed of light, when they can escape a black hole and light cannot?

Gravitional waves CAN'T escape a black hole; nothing that carries information can escape. The event Horizon is one way. The gravitational waves don't come from the singularity but instead come from ...
blademan9999's user avatar
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 ...
John Duffield's user avatar
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 ...
pela's user avatar
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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 ...
SpaceCore's user avatar
  • 3,216
7 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=...
Acccumulation's user avatar
7 votes
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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 ...
StephenG - Help Ukraine's user avatar
7 votes

Why speed of light is considered to be the fastest?

I'm standing next to Usain Bolt, he runs off in the opposite direction to the Earth's rotation, why is he consider the fastest human when I'm moving faster than him? Also there are people in planes or ...
Alex Dawn's user avatar
  • 151
6 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.
LaserYeti's user avatar
  • 736
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 ...
WarpPrime's user avatar
  • 6,673
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 ...
StephenG - Help Ukraine's user avatar
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 ...
ProfRob's user avatar
  • 153k
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 ...
Harsh Kumar's user avatar
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 ...
Florin Andrei's user avatar
5 votes

Is Earth's Surface "In orbit"?

Imagine you are in orbit around the earth, several 100 km upwards. What happens when you slow down? That's right, you fall down until some force stops your fall. That force is the pushback from the ...
Christian's user avatar
  • 673
4 votes

Are we already moving faster than light?

Short Answer NO. Long Answer - The Earth "wobbles" on its polar axis. This motion is not relevant (IMO) to the calculations needed to return to earth from interstellar space as it is an "in situ" ...
Dastagir Husain Yasin's user avatar
4 votes
Accepted

The light of which star is next to reach the earth?

I think you may be thinking of Olbers' paradox . This supposes that if the universe were infinite in time and extent, and stars were more or less randomly placed, then every line of sight would end at ...
James K's user avatar
  • 123k
4 votes
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Speed gaseous planets

There isn't such a great difference between Earth and Mars (at about 25 hours) and the gas/ice giants (between 10 and 20 hours). Earth had a day of about 6 hours in the early Solar system, but has ...
James K's user avatar
  • 123k
4 votes

Earth Versus Catastrophic Meteor

Your calculation of speeds etc is ok, and that kind of consideration might work for objects that essentially visit us once - e.g. very long period comets, or even comets that are falling into the Sun. ...
ProfRob's user avatar
  • 153k
4 votes

Does Absolute Velocity Exist?

Chris, you are actually on the verge of understanding how special relativity works. You're very close. You only need to take one extra step. to state that all speed is relative to an object is to ...
Florin Andrei's user avatar

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