Questions tagged [observable-universe]
The observable universe of a given observer encompasses the volume of space from which information - particles, radiation - could ever (past, present or future) reach that observer.
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What is the rough distribution for number of galaxies with a given mass in the observable universe?
Is there a rough formula for the fraction of galaxies in the observable universe with masses between M and M + dM? Or perhaps a graph that displays the same information? I've looked online but can't ...
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What was the size of the observable universe at the matter-dominated era and its mass density?
For instance, at the scale factor $a=0.5$ and matter dominated era, what was the size of the observable universe and matter density?
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Does expanding universe length units also expand? [duplicate]
Information
I have read an explanation about the expanding universe which represents our universe as a metal plate that tends to expand simultaneously in all directions while being heated. One can ...
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Need explanations about notions of sub-hubble and super-hubble scales
I have often seen in the literature the notions of sub-hubble, super-hubble scales as illustrated in this diagram:
I don't understand this diagram: on the abscissa is the scale factor well ...
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How a star can move out from visible universe? [duplicate]
We see only stars whose light is not older than the age of universe. This is understood. If a star is too far away that currently we don't see it then possibly we will see it later, then the age of ...
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Hubble expansion across time dimension?
The expansion of the universe, as described by the Hubble's law, refers to the expansion of space itself. This expansion is observed in the three spatial dimensions (length, width, and height), rather ...
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Big Bang and where do we stand relative to it? [duplicate]
Maybe dumb question, not sure, but I would need some help here to understand.
https://theglobestalk.com/james-webb-telescope-see-back-in-time/
So according to physics we can look back in time ...
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How/Where to find the theoretically expected cross-correlation between CMB and Large-Scale Structure in real sapce?
I have cross correlated the CMB map (WMAP 7 Year map) and the large-scale structure tracer- quasar (NBC-KDE Quasar catalog from SDSS-6 avilable here) in real space by following the this paper by ...
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Size of the observable universe and CMBR [duplicate]
Why can we detect the Microwave Background radiation (the earliest light that we can see) and not the light from stars beyond the observable universe? Should not the microwave radiation also be ...
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How do telescopes see many billion light years distant object in our universe?
How do telescopes see many billion light years distant object in our universe?
As an individual with limited expertise in the field of astronomy, my current understanding suggests that the observation ...
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Minimum Observable Offset Frequency in Leeson's Formula
It has been argued in some publications that the age of the universe represents a lower limit on observable frequencies (in their paper, corresponding to a value of $10^{-17}$ Hz). The authors do not ...
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Can we infer the size of the whole universe from its expansion rate? [closed]
If the universe inflated to 100 billion km in its first second, that suggests only 1/160,000 of it was observable from any point at that moment. The expansion rate slowed after that, of course, but ...
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Observational status of Sciama's hypothesis
I have always taken the existence of inertia more or less for granted, as an observational fact that does not require explanation.
But on reflection this is an unscientific attitude, and perhaps there ...
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Why can infinite quantities not be shown in an experiment or observed in physics?
To modern physicists knowledge, there are no truly infinite quantities that can be shown with an experiment or observation. Time is not infinite, it had a beginning. Matter and energy is finite (...
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Does only the space region movement due universe expansion affect the possibility of viewing a star?
My question is maybe simple and easy to answer because the intrinsic speed of the star affects only the final frequency of observed light but are there any tricks about the combination of object ...
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Are there any binary red supergiants?
I wonder if we ever have identified or observed a pair of binary stars (red supergiants).
And I also wonder what would happen if they exploded, (theoretically) as we havent observed it. Also, would ...
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Light emitted at $t = 0$
So solving for the scale factor from the Friedmann equation we can then use it to calculate proper distance via
$$d_p(t_o) = c \int_{t_e}^{t_o} \frac{dt}{a(t)}$$
For a particular universe $a(t)$ is ...
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If the future already exists, why can't we travel to it?
since time is actually distance, and if the future already exists, why wouldn't we be able to travel to the future? I understand humanity will never be able to, even if it was possible because our ...
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When will the particle horizon reach its limit of 63 billion light years?
In the far future, the particle horizon will reach 63 Gly，so when will that time? Just like today's universe time is 13.82 Gyr and the particle horizon is 46.5 Gly, how many years will the particle ...
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Cosmos at minimum 250x bigger than our observable Universe, so why then the need for a Big Bang?
Please correct me If I'm wrong but does not the BB only refers to our light speed limited observable Universe (OU) from our home position?
Also it is estimated that the Cosmos is minimum 250 times the ...
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Error Estimate For the Mass of the Observable Universe?
Recent interest in what is called "The Hubble Tension" brought to the fore potentially conflicting error estimates for $H_0$ as illustrated in be below diagram. I've been looking for any ...
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Is there impedance when there is nothing else?
With the exception of gravitational waves, all the information about the universe we gained from electro magnetic waves which we agree to run at the speed of light for all the spectrum from far ...
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Why don't we see the big bang?
excuse my understanding, my brain is melting.
So I understand that pictures of far away objects is like viewing the past.
and I think I pretty much get that the big bang was in every direction since ...
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Mean distance of objects of specific size in a given volume of space - visualization of planetary systems in the universe
This has been answered in this forum before in some ways I realize, but I have a rusty ability in calculus so was unable to make use of formulas!. Would love the help! I have been talking to my 11 ...
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Why the outer rim of our observable Universe is the oldest in age?
I don't get it. They telling us that the Webb space telescope will look far away from our home position deep into our observable Universe towards its outer rim about 13 Billion lyrs away where the ...
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Can the age of the universe be much bigger than 13.8 billion
If observable universe is only a small fraction of the existing universe, does it imply that the age of the universe is much more than 13.8 billion years or the expansion of the universe is much ...
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The location of the exact center of the observable universe
If simultaneously in every direction, I were to precisely measure the distance to the edge of the observable universe (not: the physical universe), then would I find myself exactly in the center with ...
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How is the expansion of the universe measured if redshift depends on the expansion itself? [duplicate]
To me this seems like a bit of a chicken egg problem.
Based on the redshift of light (plus the assumption that physics worked the same way back then and there as it does now and here), we can ...
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Is the inflation rate of the universe uniform throughout?
Is inflation constant at any given moment throughout the entire observable universe? I realize inflation was once much more prevalent, so at the edge of the observable universe, we would observe a ...
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Distribution of matter in the Universe
My teacher explained today that quantum fluctuations in the early Universe (in particular, during inflation) determined the spatial distribution of small mass inhomogeneities, which, in turn, due to ...
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Is it possible in principle to observe all galaxies in the observable universe?
Are there fundamental physical limitations that prevent the observation and cataloging of all (or almost all) galaxies in the observable universe? If there are no physical limitations, then what ...
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What are the conditions needed for baryogenesis? [duplicate]
Physicists have created antimatter in the laboratory. But when they do, they create an equal amount of matter. That suggests that the Big Bang must have created matter and antimatter in equal ...
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Why do some diagrams of the particle horizon, observable universe etc show the past light cone as hitting ~20glyr out from us at time zero?
This question is mainly in reference to this question:
Is the observable universe equivalent to 'our' light cone?,
and the answer, which is great.
But what I can't wrap my head around is why ...
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How fast is the edge of the observable universe expanding from the Earth?
If the universe is expanding at 73 kilometers per second per megaparsec, what is the fastest expansion speed that we can observe from Earth? I'm assuming that's the edge of the observable universe ...
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What would the size of the observable universe be if you traveled 3/4 the speed of light?
I have a conceptual mess in my head and would like to clean it up.
From the perspective of Earth, we can measure the observable universe diameter at current at 93BLY. I understand this and why/how ...
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Opposite of event horizon - causality horizon or sphere?
Is there an opposite of event horizon - let's call it causality horizon or causality sphere - past which current objects in space can never be influenced from Earth because of the accelerating ...
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Is "speed relative to the universe" a well-defined concept? [duplicate]
Prompted by commenting on this question.
I offered the standard "Which frame of reference are you using? Yours? A satellite's? The sun's? The Milky Way's?" observation.
Which prompted me to ...
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Is it possible that the center of the universe is outside our observable universe?
Is it possible that the universe does have a center after all, but we just cannot see it because it already fell beyond the event horizon of our observable universe?
If not, how do we know this for ...
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Can a cluster of galaxies be partially inside Hubble's sphere and partially out of the cosmological event horizon?
Can a cluster of galaxies be partially inside Hubble's sphere and partially out of the cosmological event horizon? Let say we see only that part that moves in one orbital direction e.g. moving from ...
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Why are the radius of the observable universe and radius of curvature of dark energy almost the same?
If you take the Einstein equation,
$R_{\mu\nu} - \frac12 Rg_{\mu\nu} = \frac{8\pi G}{c^4}T_{\mu\nu}$
and plug in the estimated vacuum energy of $10^{-9} J/m^3$ for $T_{\mu\mu}$, you get a spatial ...
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Another slices of the universe than space? [closed]
We observe a particular kind of "slices" of our universe: the slice that is called "space" (in the special sense of our 3 dimensional physical space).
Are other kinds of slices in ...
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What is the Poincare recurrence of the OBSERVABLE universe?
I have heard about a number called the Poincare recurrence time on Numberphile. It did not seem that exact in the way that it calculated this number, which was a power tower of 10s.
What is the ...
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Histories of the Universe under Different Initial Conditions
The history of the evolution of the Universe (we are talking about the observable part) on ultra-large scales (larger than the scale of galactic superclusters) under any initial conditions would be ...
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How do we know the universe is still expanding?
We know the expansion of the universe has been occurring due to the red shift of light from neighbouring light sources.
But given that light takes time to reach our telescopes, the glimpse of our view ...
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Thinking on a 2D plane, Is the "point" of the big bang still active?
From what I understand, the light from CMB that we can observe is the result of the last scattering from the big bang which happened 380,000 years prior to the pattern we can see.
Referencing:
While ...
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How do galaxies cross our particle horizon?
At the begin of his lecture "The Quantum Origin of the Universe" (2014) James Hartle makes the following statement:
"A new galaxy with a 100 billion stars becomes visible - ie comes ...
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Are unreachable parts of the universe 100% unreachable or do we just say so?
In Kurzgesagt's video TRUE limits of Humanity is it stated that most of the universe will be forever unreachable because the universe is expanding faster than the speed of light. This is possible ...
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What is the average rate of passage of time in the observable universe relative to the passage of time on earth?
Main Question: If you were to average out the rate of the passage of time in the observable universe relative to earth, what would it be?
Alternative Precise Question: What is the rate of passage of ...
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Is the universe that we live in a Euclidean space? [closed]
I’ve been trying to wrap my head around general relativity, and it seems to me that what Einstein really did was give up the idea of a perfect Euclidean space.
We idealize the fundamentals of physics ...
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If the observable universe is only part of the universe, how do we know there is more matter than anti-matter?
I watched this youtube video about anti-matter, which says we don't know "why the big bang produced more matter than anti-matter".
How do we know that more matter than anti-matter was ...
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