# Tag Info

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There is a great deal of effort to try an answer this question in an observational way. Or let be more precise: there is lots of effort to establish what the peculiar velocity field is in our "neighbourhood". The peculiar velocity $v_p$ is the velocity that an object has in addition to the velocity we expect to see because the object is part of the "Hubble ...

5

The question of considering every macroscopic body in the universe is formidable, mostly because on smaller scales (~sub-galactic) you need to worry about more than just gravity. Also, are you only interested in the velocity distribution at the present epoch? The universe is far from static and so it is natural to consider a time dependent distribution. ...

4

I expect you are familiar with the Big Bang model, seen here . It is a mathematical model using mathematical solutions from General Relativity and the Standard Model of particle physics . The BB developed to describe astronomical observations and the SM developed to describe particle physics observations. The SM describes how particles/nature behaves as ...

4

It seems strange to me that no one mentioned the Hubble Law. Basically, all galaxies are receding from us with "velocity" proportional to the proper distance. $$v=H_0 D$$ Where $H_0$ is the Hubble constant and the "velocity" is the derivative of the proper distance with respect to cosmological time. There are some subtleties with this definition of ...

4

Considering dark matter as a perfect fluid is useful for understanding cosmological evolution via the Friedmann acceleration equation $$3\frac{\ddot{a}}{a}=\Lambda - 4\pi G(\rho + 3p).$$ (note that this is a general relativistic equation, so not strictly Newtonian). Cosmologists use the equation of state parameter $w$ to relate ...

4

Your question is very easy to answer because the answer is just the value of the Hubble constant (or its inverse the Hubble time). The trouble is that it's hard to explain to a non-physicist what the answer means. I'll have a go, but you may find it hard going. When we are describing the expansion of the universe we can't simply talk about its size. That's ...

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We can't observe the population III stars directly so our knowledge of them is based upon computer modelling. The modelling shows that the main problem is getting the collapsing clouds of hydrogen to cool enough to become dense. It might seem a bit odd to require that the clouds cool, because after all we want the forming star to get hot enough for fusion ...

3

Despite the comments, this question can be answered with physics. You didn't specify what you mean by either "everything" or "doubles in size" so I'll assume you meant all massive objects double in length along each orthogonal spatial dimension while maintaining their form and composition. The apparent speed and actual speed are unchanged. A radar dish on ...

3

If we want to observe the universe expansion with the most straightforward and direct way we have to measure redshifts of galaxies. The minimum distance where this effect would start to be observable is that at which the speed of recession is larger than the average noise speed, which is around a few hundred $km/s$. Given that the value of the hubble ...

3

At the moment we don't know what dark energy is so we formulate hypotheses and compare them to the experimental data. The two most popular hypotheses are: dark energy is due to a cosmological constant dark energy is a scalar field referred to as quintessence and both of these have the property that the total energy inside a volume of space increases as ...

3

The Earth also radiates more energy than it receives from the Sun. There are many mechanisms by which an astronomical body can generate heat, and nuclear fusion is just one. In the case of the Earth the extra heat is generated by radioactive decay in the Earth's core. There is an excellent discussion of the source of Jupiter's excess heat in this article ...

3

The universe is described by a scale factor, normally indicated by the symbol $a(t)$, that is a function of time. We take the scale factor to be one right now, so in the past $a$ was less than one and in the future $a$ will be greater than one. Roughly speaking, if $a$ has the value $\tfrac{1}{2}$ it means everything was half as far apart as it is now, and ...

2

If we are moving relative to the CMB then CMB photons will be doppler shifted (and the amount depends on the direction relative to the CMB frame). This induces a dipole in the temperature fluctuation map $$T(\theta) = T_0(1+v/c\cos\theta)$$ to first order in $v$, which we can measure. The direction and velocity can for example be found by fitting a dipole ...

2

We can explain everything we see in universe by just assuming the rest mass of any particle decreases with time. Therefore the gravitational force will be zero. See for details this link https://www.scribd.com/doc/279174920/Decreasing-Mass-Cosmology-and-the-Accelerating-Expansion-of-the-Universe

2

I've located a paper that goes into great (excruciating?) detail on the 21cm power spectrum (of baryons) in the dark ages. I won't pretend to have the expertise to understand the whole thing, but I'll try to bring out a couple of relevant points here. Note that this is all theoretical work in the framework of the standard cosmological model since actual ...

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You conclude: "My intuition is that with 100's of M's of years to even out and settle down, it would be surpassingly smooth and quiescent." According to the history of the universe here , the dark ages happen after the decoupling of photons and the Cosmic Microwave Background radiation which happened around 380.000 years after the Big Bang. CMB is ...

2

The cosmological data from observations have been fitted with the Big Bang model. Fitted means that a mathematical formula is used which fits the data with acceptable errors. One has to be clear that mathematics is not physics. That the formula fitting the observations has a singularity at the beginning of its functional form, does not mean that physical ...

1

A magnitude is a somewhat convoluted measurement of luminosity. You probably have relative magnitude $m$ per $\rm arcsec^2$. You can start by using the distance modulus $m-M$ to calculate the absolute magnitude $M$: $$m-M=5\left(\log_{10}\left(\frac{d}{\rm pc}\right) - 1\right)$$ where $d$ is the distance. Once you have the absolute magnitude you can ...

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What evidence is there for additional dark energy coming into existence when space increases? None. As I understand since cosmological constant is a 'constant' - increasing the space must generate additional dark energy that fills that space That's what people say. But we have no evidence whatsoever of anything wherein conservation of energy does ...

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Wikipedia has a specific section on it in its lambda-cdm model entry. It cites a publicly available peer reviewed paper published by ESO in 2015.

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First, you make a measurement of the CMB temperature map. With the average temperature subtracted off, this looks like: The main feature to see here is a clear dipole, the signature of the doppler shift caused by the motion of the detector relative to the CMB rest frame. There's also a bit of fuzz visible along the equator from galactic foreground ...

1

There is a huge huge problem here. You could be a Boltzmann brain. But to calculate the probability that you are a Boltzmann brain we have to have a theory about the way the universe is and then quantify how many Boltzmann brains that universe has compared to how many real brains it has. But you want to compute a probability. The only way to compute a ...

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All the "rules" you listed, which describe the Big Bang process and subsequent universe, are concepts of how forces of nature interact. The forces of nature themselves - strong nuclear force, weak force, electromagnetism, and gravitation - may have emerged, along with time itself, from the Big Bang process. Without time, the rules would make no sense. ...

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The CMB radiation is the "temperature of the universe" Approximately 379 000 years after the Big Bang the ionized hydrogen (free protons and electrons) had cooled down to about 3000 K, and thus became "transparent" hydrogen due to ionization ceased. For each time point later the hydrogen cooled down "exactly" as much as the universe expanded. In other ...

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Rather belatedly, let me mention my answer to Did the Big Bang happen at a point?. This explains the geometry of the expanding universe in laymans terms, and should make it clear how it differs from the geometry of a black hole. because the geometry of the two solutions is completely different there is no reason to expect them to evolve in the same way, and ...

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Types of observations (at least): Lyman $\alpha$ forest at $z\approx 2.5-6.5$ Thomson Scattering Optical depth for Cosmic Microwave Background radiation Intergalactic Medium temperature at $z<\approx 6$ Lyman $\alpha$: One method: An absorption phenomenon seen in the spectra of background quasi-stellar objects. Based on the neutral hydrogen ...

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When treated properly, one has to study Einstein's equations with the dark energy as the source. For example, when the dark energy is cosmological constant (the most important subtype of dark energy), the resulting spacetime is a de Sitter space, a Minkowski-signature type of a hyperboloid. Galaxies move along geodesics and those geodesics are "repelling" ...

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Earth is moving around sun in an orbit with mean radius 1AU. Time of one revolution is 1 year . Thus, its speed is $$v \approx 2 \pi \dfrac{1AU}{1year} = 30km/sec$$ . Sun moves s=around galactic center at a speed of $v'=220km/sec$. Thus, when you are standing still on Earth,you can have a velocity of $v'+v$ with respect to center of Milky way galaxy. This ...

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