r/cosmology

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?

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!

Ask your cosmology related questions in this thread.

Please read the sidebar and remember to follow reddiquette.

A recent Reddit poster wrote: "No one wants to see space x succeed as long as Elon is a part of it" This is my response.

I don’t think that is the case. Some people have certainly become discouraged by Elon Musk’s behavior or have lost confidence in Starship, but that does not represent the large majority of people who support the human exploration of Mars and the rest of the solar system.

All Mars Society members and other space-exploration advocates still want SpaceX and Starship to succeed. The program is far larger than any one individual. Thousands of highly skilled SpaceX employees—including engineers, scientists, technicians, and construction workers—are doing the difficult work of designing, building, testing, and improving Starship.

My view is simple: I want Musk to continue providing the financial backing and resources needed to keep that team working. I do not have to agree with his politics, personality, or every decision he makes in order to recognize the importance of Starship’s potential.

Gwynne Shotwell and SpaceX’s experienced leadership and engineering teams provide valuable operational knowledge and stability. Starship is not being built by Elon Musk alone; it is being built from top to bottom by a large and extraordinarily capable workforce.

Musk has also made decisions that deserve criticism. One example was the decision to conduct a Starship launch without a flame trench and a fully developed water-deluge system. The resulting damage to the launch site contributed to delays and extensive reconstruction. In my personal opinion, the pressure to launch quickly may have outweighed the caution that such a powerful rocket required.

We can criticize Musk when criticism is deserved while still supporting the thousands of people working to make Starship successful. Wanting SpaceX to succeed does not mean approving of everything Elon Musk says or does. It means recognizing that Starship may still play an essential role in opening Mars and the solar system to human exploration. We wish the SpaceX Starship team success and remain among its strongest supporters.

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?

View Poll

I've heard all the arguments. I've read all the theories. And yet my logic and instincts tell me that space, also known as emptiness, never ends.

My very atoms (which do not contain planet-like electron orbitals) tell me so. They don't really, I just wanted to sort of insert a little dig at the planet-like orbital deception.

In any event, nothingness can't just stop.

And I'll tell you something else: I've long said that space is the sole thing in existence to which the term infinite can apply.

This debate is irresistibly compelling and triggering to me. It's triggering in that people talk so much drokking nonsense in discussions on the subject.

People, myself included, have such fierce opinions regarding the possibility of space being literally infinite. This endless debate provokes real emotions.

Thank you.

Ask your cosmology related questions in this thread.

Please read the sidebar and remember to follow reddiquette.