# Tag Info

0

Quick fun analogy: If we think of the expansion of space as a sheet stretching, particles of matter move away from each other. Hooray, as explained several times before. Extending this to 3D, we're basically stretching objects at a very slow rate. 1.62038964 × 10^-17 m/s / meter, to be precise. Thus, a typical person is stretched at about 3x10^-17 meters ...

3

The first thing I want to introduce is the standard candle, which is an astronomical object with a very well known luminosity and emission profile. One of the best standard candles we have is the Type 1a Supernova. This type of supernova only occurs in a very specific way such that all type 1a supernovae have approximately the same luminosity and emission ...

3

There are basically two measurements which take place here: (i) the redshift of the supernova (ii) the peak brightness of the supernova (though this latter is a bit more complicated than that). The distance is not found from the redshift, it found from the apparent brightness of the supernovae. The supernovae in question are Type Ia and act as "standard ...

1

There is a very common misconception that matter exploded outwards from a point in a pre-existing universe at the time of the Big Bang. This is not, however, what the Big Bang theory claims. Instead, the universe was still infinitely more dense than it is today, but was the same shape (in the topological sense). If the universe is infinite in size today, ...

5

Even in special relativity, the claim that light always travels at a constant speed of c is only true in inertial reference frames, in non-inertial coordinate systems like Rindler coordinates, the coordinate velocity (change in position coordinate with respect to coordinate time) may vary. In general relativity, all coordinate systems covering large regions ...

5

If they are much far away will they have relative velocity of separation greater than speed of light and if so how can we even detect such galaxies. We can't detect such galaxies. Redshift goes to infinity at the cosmic horizon, and we cannot see beyond. Note that the cosmic horizon is different from the Hubble sphere: At the former, relative velocities ...

2

These galaxies are not out of reach. The Hubble Sphere is the volume of space surrounding an observer where everything inside the sphere moves away from the observer with a speed less than c. Following this logic it immediately follows that the Hubble Sphere is equivalent to the cosmological event horizon that @Hritik is discussing in his answer. ...

3

Such galaxies cannot be detected. and Quantum entanglement is just a correlation between two bits of information and it no way does, and no way can be used to transfer information faster than the speed of light. Any light sent from such galaxies towards ours would show a wavelength of infinity after considering Doppler shift. In short these galaxies can ...

3

In this paper by Gott et al., on p. 466 they define the "future visibility limit", saying in the published version that "No matter how long we wait, we will not be able to see farther than this", and on p. 7 of the arxiv preprint they similarly say "If we wait until the infinite future we will eventually be able to see the Big Bang at the co-moving future ...

9

If our ideas about cosmic evolution are correct, galaxies that are visible today will in principle remain visible in the future. As time goes on, light from more and more distant galaxies will be able to reach us, and the number of observable galaxies will increase. However, there exists a cosmic event horizon$^1$, so this is an asymptotic growth: There's a ...

0

If the Universe is infinite, then it had instantly grew from zero to infinity at the moment of Big Bang. Note, that this is a possible model from General Relativity (GR). But most probably GR is not applicable at the moment of Big Bang, because it contains singularity.

0

The accelerated expansion of the Universe is an effect of repulsing forces BY DEFINITION. The nickname of the reason of these forces is "dark energy". The problem is that Einstein's $\Lambda$ term is very simple addition to equations. It could be added even if Einstein didn't want to make Universe static. So it is a great possibility, that Einstein didn't ...

2

The simplified model of the universe used in discussions like this is the FLRW metric. From the tone of your question I'm guessing that you're not looking for a detailed mathemtical treatment, so let me just pull out the equation that answers your question. This is one of the two Friedmann equations: $$\frac{\ddot{a}}{a} = -A\rho + B\Lambda \tag{1}$$ ...

0

The universe was infinite at its creation, and continued to be so. It just got bigger during inflation. There may be a misconception that the universe begun as a "infinitesimal point", but singularity just means that it was non-defined. During inflation, the space between matter became wider, analogous in 2-dimensions, to the "spots on a balloon's surface" ...

0

So, we first have to understand what it actually means to be 'expanding.' The FLRW Metric describes our universe as homogenous (physics works the same at all points), isotropic (looks basically the same everywhere on a large scale), and expanding. In simplest terms, the further back in time we look, the closer things generally seem. Basically, objects that ...

0

I think there is no more "slow" light from the begining od the universe remaining because photon has accelerated after expansion to reach their current speed. Maybe I'm wrong but to me it seems to be the right way to think.

3

There are scientists that do not accept the Big Bang (and more). That doesn't mean that there isn't evidence for the Big Bang (there is), nor does it imply it may be wrong. All we can say is that some scientists consider the Big Bang to be a fact because the evidence is overwhelming, some who think it is the best cosmological model because there is much ...

2

@GeorgeSmyridis: the big bang is a model that describes a bunch of cosmology. Physicists, when referring to it, rarely are talking about the event that happened at the very beginning of the model. In fact, the situation in the model goes outside of the applicable region of known physics before you get to the point in time when the explosion would have ...

Top 50 recent answers are included