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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
  • 125k
66 votes

How did Hubble know the red shift difference between "moving away" and "old"?

The "redshift" measurements that Hubble used to determine his law are based on looking at the spectrum of distant galaxies. That is, splitting the light coming from the object in its ...
TimRias's user avatar
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17 votes

What would evidence of stars and galaxies significantly older than 13.8 billion years old look like? In what parts of space has it not been found?

Assuming the cosmological principle still holds, then we might expect that your own galaxy and those around us should contain evidence of stars/objects older than 13.8 billion years old. These might ...
ProfRob's user avatar
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15 votes
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Is the age of the universe relative to an observer's location in that universe?

You are labouring under the misapprehension that how far we can see directly gives the age of the universe. Whilst it is true that the oldest light we can see was emitted some 13.7 billion years ago, ...
ProfRob's user avatar
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12 votes
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Age of a black hole

From looking at the Black Hole alone, there is no possibility of determining its age. The state of the Black Hole is fully determined by a few fundamental variables (mass, angular momentum and ...
Sir Cornflakes's user avatar
11 votes
Accepted

Does the age of the universe take into account General Relativity / Special Relativity?

Rob Jeffries gives a good response to this question, but I wanted to go through the basic outline of how the age of the universe is calculated, just so you can see how it works more or less. Be warned ...
zephyr's user avatar
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11 votes

Does the age of the universe take into account General Relativity / Special Relativity?

This is a confusing question - your title mentions GR, but of course the age of the universe is entirely derived as a result of using GR to solve for the dynamics of the expanding universe. The text ...
ProfRob's user avatar
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11 votes
Accepted

How far would EGSY8p7 be away now?

30.4 billion lightyears. The current distance — i.e. the distance that one would measure if we froze the Universe and started laying out measuring rods — is called the proper distance, or physical ...
pela's user avatar
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10 votes

Is the age of the Universe really 13.8 billion years?

The age of the universe is not calculated based on the size of the visible universe. The age of the universe is being calculated based on the fact that the laws of nature have no direction. This means ...
MacUserT's user avatar
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9 votes
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Do we know how old the matter that makes us is?

The material (heavier than helium) that makes up the solar system was made in millions, if not hundreds of millions of stars that lived and died in the ~7 billion years between the formation of the ...
ProfRob's user avatar
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8 votes
Accepted

Why is the main sequence often called 'zero age' main sequence?

The zero age main sequence (ZAMS) is the theoretical locus of points in the Hertzsprung-Russell diagram where the luminosities of young stars (at a range of masses) are mostly supplied by the nuclear ...
ProfRob's user avatar
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8 votes

Is the age of the Universe really 13.8 billion years?

There are many extremely widespread misconceptions about cosmology. One is the idea that there's some importance to cosmological recession speeds larger than $c$. In reality, recessional speeds are ...
benrg's user avatar
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7 votes
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Is our universe flat?

And also there are some terms related to black holes, 3D shape, ball etc. Apart from those complexity, my intention is simply to be clarified, why we call our universe flat? And by word flat, what ...
Helen's user avatar
  • 399
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

Could a star closely orbit a black hole long enough for the star to have lost 0.5B+ years to time dilation?

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 ...
Anders Sandberg's user avatar
7 votes

How did Hubble know the red shift difference between "moving away" and "old"?

Disclaimer: I am not an astronomer or physicist. I welcome any corrections or clarifications. Star color The light from stars and galaxies has a color. For stars that are close enough and bright ...
Katie Kilian's user avatar
6 votes
Accepted

How to evaluate the fit of an isochrone to a stellar population?

Finding the best-fitting isochrone, a.k.a. isochrone fitting, is a standard approach to determine the age of globular clusters. This problem can be solved with a least-square method, where the data to ...
NGsp's user avatar
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6 votes
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Could a star closely orbit a black hole long enough for the star to have lost 0.5B+ years to time dilation?

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 ...
TimRias's user avatar
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6 votes
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How to determine the age of a star using asteroseismology?

Asteroseismology effectively measures the sound speed inside a star by finding the characteristic oscillation frequencies of a star. The sound speed depends on the composition because the pressure at ...
ProfRob's user avatar
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5 votes
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Use of type-I a supernovae as standard candle

A type 1a supernova forms when a white dwarf grows through accretion to a certain size, at which it becomes unstable. This means that the precursor object is always a white dwarf of mass 1.39 solar ...
James K's user avatar
  • 125k
5 votes
Accepted

What have we learned from the observation of most distant galaxies

Nearby galaxies are seen in their old age. Distant galaxies are, on average, the same age as the local ones. But due to the finite speed of light, the farther you look, the younger you observe them. ...
pela's user avatar
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5 votes
Accepted

Absolute model ages of lunar craters

First, Terminology: Age is how old something is. Relative age is how old something is when compared to another (older vs younger). Absolute age is putting a number on that age (I am XX years old). ...
Stuart Robbins's user avatar
5 votes
Accepted

How slow would you age on a double gravity planet?

A simple way to calculate the gravitational time dilation on the surface of a planet comes by assuming that the planet is spherically symmetric other sources of gravitational potential (a star, a ...
Prallax's user avatar
  • 4,431
5 votes

Does "Angular Diameter Turnaround Point" solve the Great Wall Problem?

Expansion of the Universe, not of small structures It is true that large "structures", such as unvirialized clusters, and voids, scale with the expansion of the Universe, but smaller ...
pela's user avatar
  • 38.7k
4 votes
Accepted

How can we tell the age of a rogue planet?

At the moment there is basically only one way. That is to associate the planetary-sized object with a cluster of stars or moving group of stars of known age. That's basically it. If the planetary-...
ProfRob's user avatar
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4 votes
Accepted

Redshift to calculate age of stars

The redshift that is referred to is not a Doppler redshift, but a cosmological redshift. The difference is that the former is caused by the source moving through space, while the latter is caused by ...
pela's user avatar
  • 38.7k
4 votes

Is our universe flat?

Flat here means "has Euklidean geometry" (on large scales), as explained by Helen's answer. Observationally, the universe appears flat, i.e. any deviations are within the uncertainties. Of course, if ...
Walter's user avatar
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4 votes
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Long-lived supernova remnants?

Of the order 10000–100000 years. As an example of an old Supernova remnant, you can see the Vela SNR, estimated at 11,000–12,300 years old. Nasa describes the evolution of a remnant Initially, the ...
James K's user avatar
  • 125k
4 votes

Do black holes have "age" when they form?

It depends on the context, since "age" is not a trivial concept for nonliving entities. If you're interested in the connections between stellar evolution and black hole evolution, then you ...
Daddy Kropotkin's user avatar

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