49
votes
Accepted
How can telescopes see anything at all?
Yes, space is very empty. There is not nothing between us an the Eagle nebula, but little enough that we can still get a reasonable view of it.
The pillars are ephemeral, they are evolving on ...
- 146k
24
votes
Accepted
Approximately what percent of the sky has nothing in it?
It is really quite hard to answer the question as posed because as you observe deeper and deeper (e.g. using a larger telescope or observing for longer) then more and more (fainter) objects become ...
- 146k
22
votes
How can telescopes see anything at all?
Does that mean that between those 7,000 light-years, there's absolute nothing in the way that obscures the pillars? Given it's arcseconds, I'd expect that any kind of disturbance would make it simply ...
- 407
18
votes
Accepted
Could the redshift of all incoming photons be explained by a massive ring of distant masses pulling the sources of the photons away?
You have identified the issues.
The model does not explain the redshift-distance relationship, which is one of the primary pieces of evidence.
Simply to say "our ideas about gravity are wrong&...
- 146k
17
votes
Approximately what percent of the sky has nothing in it?
Zero. At the limit, there's the Cosmic Microwave Background which represents the content of the Universe not long after it came into being.
Of course, some would no doubt propose that since the CMB ...
8
votes
Approximately what percent of the sky has nothing in it?
Following on @mlk's suggestion to do Olbers' paradox in reverse, I'll try to estimate how much of the sky ends at a visible star (i.e., emitting something in the visible range, so that it could ...
- 454
7
votes
Accepted
Conditions in the Early Universe
Here are some plots, calculated as described here. I assume no physics beyond the Standard Model and the concordance cosmological model.
The temperature
The horizontal lines are:
The temperature of ...
- 4,260
4
votes
Could the redshift of all incoming photons be explained by a massive ring of distant masses pulling the sources of the photons away?
If so, there would be an area in the middle of the sphere/ring where the galaxies are not moving away from each other, and it would be easy to detect the gradient of movement from the center of the ...
- 4,188
4
votes
Accepted
What is the rarest stable element in the universe?
Within our solar system the least abundant, stable and non radioactive element is Tantalum, atomic number 73.
Its chemical inertness,
make it valuable for laboratory and industrial equipment such as ...
- 2,169
3
votes
Approximately what percent of the sky has nothing in it?
This is supposed to be a very rough ballpark estimate on what percentage of the sky is covered by stars in the milky way galaxy.
There are approximately $10^{11}$ stars in the Milky way. First ...
- 191
3
votes
How did we measure the mass of the universe?
The mass contained within the observable universe is found by mutiplying its volume by an average density derived from the assumption that the universe is flat with the amount of matter given (as a ...
- 146k
3
votes
Size of the whole universe if it were spherical
Different data sets, analysis methods, and statistical interpretations will give different limits on the ratio $\Omega$ between the density and the critical density. However, let's adopt $\Omega=1....
- 4,260
3
votes
Other Hubble spheres with no Lorentz symmetry?
Lorentz symmetry is only global in flat space times; in free falling general relativistic reference frames, it is a local symmetry. So you don’t even have to go as far as outside the observable ...
- 3,404
2
votes
Accepted
What natural astronomical object is rare on a Hubble volume scale?
The space density of ultraluminous quasars (those with luminosities greater than $5\times 10^{13}L_\odot$) in the local universe is $\sim 10^{-9}$ (Mpc)$^{-3}$ (see for example Caplar et al. (2015) ...
- 146k
2
votes
Formula for rate of expansion of the universe vs distance?
The relationship between proper distance and the rate of change of proper distance is Hubble's law. So
$$ v(r_0) = H_0 r_0 \ .$$
Note that $H_0$ is the Hubble parameter at the present epoch. The ...
- 146k
1
vote
How can telescopes see anything at all?
I can't speak to the creation of a photo of Pillars of Creation specifically, but in general:
I'd expect that any kind of disturbance would make it simply impossible to visualize it.
Your question ...
- 381
1
vote
Is the universe still considered "finite but unbounded"?
We don't know the topology of the whole universe. If the universe has a density critical density of $\Omega>1$ it could be "finite but bounded" but if $\Omega\le1$ then it could be open ...
- 116k
1
vote
Approximately what percent of the sky has nothing in it?
Approximately 100% if you assume the cosmic microwave background to be actually a background and not an object on its own rights.
This is why the sky is black in the first place. It consists of stars ...
- 2,784
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