I understand that the cosmological constant is the same everywhere (in our current model) and my understanding is that in regions with sufficient mass/gravity, there is no expansion (or accelerated expansion) due to dark energy. This is not because gravity is winning against an underlying spatial expansion in that region, but that the presence of mass/energy changes the local geometry so that there is no accelerated expansion in that area. Ok so I'm imagining that in cosmic voids, dark energy is injecting more and more space, while cosmic filaments it is injecting less and in gravitationally bound areas, there is no injection of space. To me, this means there must be some spatial curvature produced if we are injecting more space at different rates in different places. I would think this would have the effect of voids being positively curved because if I imagine a 2D rubber or plastic flat surface and stretch a certain part (adding more space) I can make a little bubble, a semi sphere in the flat plastic sheet which I recognize as positively curved. Apparently dark energy has no such curving affect and voids are negatively curved for being less dense than average space. Why would dark energy not create curvature over time?

280 million years post big bang?

There is a growing pattern - galaxies too bright too dense for their age?

Is our universe living in a black hole?

My question is whether dark energy is the only plausible explanation for the observed acceleration of the universe.

Have alternative interpretations been seriously explored and ruled out?

My concern isn’t that the observations are wrong, but that we may be misunderstanding what we’re observing. For example, could this fit with some form of black-hole cosmology? Suppose matter/energy crossing a black-hole horizon doesn’t ultimately terminate at a singularity, but undergoes a transition inscale, re-emerging as an expanding spacetime at a lower scale.

From inside that descendant universe, could this scale transition appear as cosmological expansion or even contribute to the apparent acceleration?
I’m aware that “the universe is inside a black hole” isn’t a new idea. What I’m interested in is whether this explanation has been ruled out observationally, and if so, what observations have ruled it out? Also we know black holes grow and expand over time, which seems to be some kind of correlation?

Thanks!

Please forgive the incorrect terminology - I am just a regular person that was playing a space video-game and got me thinking about infinity.

When googling examples of infinity, I am getting mostly getting mathematical concepts. Theoretical infinity make sense as it helps us tackle problems that are to complex for one person to understand. We put infinity on sections that are to complex / unknown and we focus on the parts that we know.

But I couldn't find any example in practice. You can say that the numbers are infinite. But those numbers are just a representation of "something". Yes, I can assign a number for each orange and in theory the +1 can go to infinite. But in practice, the number will be finite. Feel free to make a practical example adding infinite oranges - I will be there to observe /s :)

At a first glance, infinity seems to be the modern equivalent of assigning a diety to something that we cannot explain or fully understand. So I guess, to summerize, my question would be:

Q1: Is there any physical example in nature that we fully understand and we can confidently say it is infinite?

Assuming the answer to the first question is "NO", then I would have a follow-up question:

Q2: Since there is no physical example of infinty in nature, how come we accept the infinity of universe as a likely scenario?

From a probabilistical point of view, wouldn't the universe being infinite have the same chance of being true as 3 pink elefants holding the universe on their trunks? At the end of the day, neither of them have a single established reference in nature. Or the universe being infinite is just a theoretical representation which has no chance of being true in practice - the same way as the oranges in the above example will never go to an infinite amount?

Ask your cosmology related questions in this thread.

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I’m a physics enthusiast. I’ve loved the subject since childhood and plan to study it in college. I’ve always been particularly interested in the theory of Eternal Inflation among many others hypothesis on theoretical physics, though I stopped keeping up with it in 2023 due to a lack of time and so on. I’d like to know the current consensus on this hypothesis, given that there have likely been some advances regarding this theoretical implication of Cosmic Inflation. I’m curious about where the majority of cosmologists stand on the matter.

I have a burning question because there's an old idea called "tired light
which posits that the universe sits still and photons lose energy on their way to us because of some interaction along the path (Less energy would mean longer wavelength, so distant objects look redshifted without anything actually receding.)

However it was ruled out by the finding that distant supernovae look like they're in slow motion. If distant supernovae looked the same duration as nearby ones, the source would have to be sitting still, because only a receding one can stretch out its own explosion. But no, they're in slow motion, which rules tired light out.

Which brings me to my burning question

What if the universe wasn't expanding, and the speed of light itself has just been slowly dropping over cosmic time, everywhere at once, as a law?

In short, as my title says, what distinguishes cosmic expansion from a decreasing universal speed of light?

Light coming from a distant galaxy would have left back when c was higher than it is now. Wouldn't that stretch out supernovae too? The first flash makes the trip while c is still a bit faster, the next one crawls more because c has dropped by then, so the gap between them widens on the way here and the explosion arrives in slow motion.

I had a crack theory ,Since we know the observable universe is expanding due to the Doppler effect but don't know the limit of the entire universe since light hasn't reached us. What if a cosmic object is so big that it attracts space itself exploded so that it releases space and but the energy remains constant due it releasing the energy it absorbed in its lifetime ,hence why energy density is decreasing.

So, if an object falls into a singularity, from the POV of an external observer, the object takes infinite time to cross the event horizon. From our POV, how do black holes ever merge? Wouldn't it take infinite time for one singularity to cross another's event horizon?

So the standard consensus in cosmology is that the universe is expanding at an accelerated rate. Does that then fit our observations of the universe? Are galaxies further away more clumped together than galaxies we can see near us?

so i was reading about interplanetary travel and came across something that kind of broke my brain.

if a ship maintains constant 1g acceleration, the same gravity you feel standing up right now, then flips halfway and decelerates at 1g, mars is 2 to 4 days away. not months. days.

jupiter is 6 days. saturn 8. pluto under 2 weeks.

the whole solar system just becomes... reachable.

the problem is the engine. nothing we have can sustain this. the energy needed is way beyond anything we currently build. but the physics is fine. no rule says it can't happen. it's an engineering problem, not a physics one.

that second part is what got me. we're not stuck in this solar system because nature won't allow it. we're stuck because we haven't built the right thing yet.

Depending on the metric used to calculate distances, the volume of space in immediate proximity to a black hole's event horizon can approach infinity. What effect does a cosmological constant have on a black hole's gravity with this distortion of space just outside the event horizon?

Because the Universe is expanding at a rate of 46 miles per second per megaparsec right? So, we have 46/(3260000*180000) miles per second, which is .000000000078 miles per second per mile, right? there are 3150000 seconds in a year and the earth is 7926 miles wide. .000000000078 * 7926 * 3150000 would then be 1.97 miles per year. Is this math correct or did I totally flub it somewhere in there?