If the physical community is to be believed, Anti de Sitter (AdS) space-times provide no possibility to explain cosmological observations. This is usually explained by the contrast between the negative cosmological constant in AdS space-times and a positive cosmological constant which is necessary for the observed accelerated expansion of the universe.

However, if we allow a fifth dimension, then Einstein’s equation can realize a five dimensional cosmological constant Lambda_5<0 and a four dimensional cosmological constant Lambda>0 on hypersurfaces where Friedmann's equations live (cf. Brane world cosmology).

Since Friedmann’s equations are the basis of the standard model of cosmology, fine-tuning of the model parameter for the epochs after nucleosynthesis leads to the standard model of cosmology. The unknown mechanism to explain the values of the fine-tuned parameter makes this AdS model more problematic than the standard de Sitter model.

A second disadvantage becomes visible when AdS space-times are examined a little more closely.

A five dimensional asymptotically AdS space-time (the bulk) solves Einstein’s equation with a negative cosmological constant and can be expressed asymptotically such that the boundary is reached in the limit r -> 0. The hypersurfaces with r>0 are called brane and can labeled by their coordinate r. The boundary is important for the duality between AdS space-times and conformal field theories (CFT). For example, the bulk space-time can be holographically reconstructed form the boundary data. The problem with the above AdS cosmology model is that the gravitational action and therefore the energy-momentum tensor diverges at the boundary.

In a recent work, I have used a renormalised action by subtracting the divergent terms. Then the renormalised and therefore finite energy-momentum tensor wa

The Poincaré recurrence theorem basically states that distinct dynamical systems will return to a their initial state or somewhat close to the initial state.

Andrei Linde's cosmic inflation models our universe may a Poincaré recurrence time within 10^10^10^10^10^1.1 Planck times. One Planck time is 5.391×10^-44 seconds.

In de-Sitter space, thermodynamical systems of the Poincaré recurrence time is exponentially large in the Boltzmann entropy of the system. However, Kolmogorov-Sinai entropy and could theoretically, be considerably shorter. If there is anyone doing interdisciplinary research between thermodynamics and cosmology, please chime in on this because I'm not an expert in that arena.

However, when considering quantum fluctuations, the Casimir-Polder experiments, quantum tunneling and quantum vacua, it is argued that de-Sitter space is meta-stable. The quantum breaking time and a meta-stable vacua may cause inflationary bubble nucleation.

What do I think about this?

As a person who is in the nascent stages of pursuing interdisciplinary research between materials chemistry, electrical engineering and quantum cosmology, I stress the importance of apparatuses, experiments and observations.

I infer that the transition-edge-sensor bolometric detectors on the Probe of Inflation and Cosmic Origins (PICO for short) would be able to lend some evidence for or against the hypothesis that a Poincaré recurrence time may occur within 10^10^10^10^10^1.1 Planck times (this is on the basis of stochastic inflationary models).

PICO will attempt to detect the primordial gravitational waves that emerged from cosmic inflation and within a confidence interval of 5σ. 5σ is a confidence level of 99.99994% within a standard deviation.

I'm reading Katie Mack's "The End Of Everything" at the moment, and actually have a question about part of it, if somebody more knowledgeable would like to clear something up for me:

In the chapter on Heat Death, the author writes about the de Sitter universe, and how this would be a state of maximum entropy, where entropy cannot increase and the arrow of time is just gone.

Then she mentions that statistical mechanics might allow an "out", in that if you wait long enough, random unpredictable fluctuations might shift parts of the system into a lower-entropy state.

Does she mean that this could happen before the total heat death, as there is no arrow of time in a de Sitter universe? Or would that be in a de Sitter universe, where randomly entropy goes down in an area, and in that area (alone) you would then have time again? How does one wait a very long time if there is essentially no "time"?

http://imgur.com/a/2hcYVzx can someone explain when the moment has this expression? X are comoving coordinates, I would put a instead of a^2

Fala pessoal blz?

Alguém recomenda algum cuidador de gato, que vem em casa, troca água/comida/areia, uma vez por dia? Região de perdizes e tals, obrigado!

(Note: Please consider starting with the added note in the comment below the original post.)

I am not a scientist or anything so please take the following with the proverbial grain of salt. The chance of having misunderstood something is also very possible, so please indulge me for a few moments.

At the risk of getting things wrong, and with my knowledge about string theory being very limited: Listening again to someone describing the damning negative curvature of string theory ideas as being something unrealistic (anti-de Sitter space I guess), I was thinking perhaps a change in perspective might perhaps make this negative curvature allright in some specific sense, explained below.

I don't know how string theory is supposed to work, but if a negative konstant curvature is deemed unrealistic or inappropriate to our universe, then perhaps a change of perspective might sort things out I was thinking.

For this general idea to make sense the way I imagine it, you would have to incroporate an idea of a dynamic universe, which I guess is not what scientists think of the universe today, in that I guess they refer to the universe as a universe having a fixed thermodynamic background.

My crude understanding is that physicists very much like their fixed thermodynamic universe, but nevermind that.

The way I imagine a solution for making something negative konstant into a simple constant:

So if you conceptualized a dynamic universe as be perpertually constituting our known universe with a full wave only like system (obviously an abstraction), then instead of relying on a wave-particle duality regime for figuring out what 'energy' is with ideas of entropy; if instead you imagined a perpetual wave like propagation of energy on a basic "future" time aspect (something that happens before the present), which so to speak was "beneath" all of the current world of subatomic particles, but also explained gravity; then I imagine that the 'negative konstant curvature' of anti-de Sitter space could instead be interpreted as energy in two forms of "gravity-as-acceleration".

**"Gravity-as-acceleration"**This notion of thinking of 'energy' being acceleration in two forms, is here thought of as a wave regime (or a wave energy paradigm if you will) that somehow (don't ask me how) have energy propagate by perfectly harmonic and either self accelerating waves, or, a source; and then, what is thought of as typical gravity could be a form of 'drag' effect as

Having read https://arxiv.org/pdf/2112.03947.pdf, https://arxiv.org/pdf/1903.00009.pdf and https://arxiv.org/pdf/1903.00009.pdf, I noted the use of MSSM ( Minimal Supersymmetric Standard Model ) as if equivalent to SM, yet it is instead supersymmetric. They show derive some or a lot of MSSM models including in 4D. There are many more related papers.

Question 1: has any derivation from F-theory, led to SM (i.e. non supersymmetric)? I see mention of supersymmetry breaking but no mention that it would not still involve MSSM.

Question 2: There are many arguments to suspect that de Sitter Vacua are in the swampland (except for the de Sitter vacua construction schemes that define spacetime effective potentials that are positive and stable metastable or unstable). Is anything different for F-theory (especially when at 4D). I haven't seen any result suggesting extracting a de Sitter vacuum from the derivation of 4D models from 12D F-theory. Is there any? I asked because of section 4.3 in https://arxiv.org/pdf/hep-th/9602022.pdf that relies on https://arxiv.org/pdf/hep-th/9506101.pdf with non supersymmetric strings in 4D to explain the small cosmological constant. Would the broken supersymmetry allow de Sitter vacua then and be in the string landscape.

https://shmaesphysics.wordpress.com/2020/09/19/renormalization-and-asymptotic-safety-of-gravity-in-a-multi-fold-universe-more-tracking-of-the-standard-model-at-the-cost-of-supersymmetries-guts-and-superstrings/comment-page-1/#comment-3187

I think a big change they need to do is clothing. yes you can limit yourself and say only one change per day or no changes at all but most people will almost always exit a convo flash an NPC and change outfit just to ask them a question. I think maybe a good change would be forcing someone to have all their clothes in a wardrobe and you pick one outfit before you leave your room and if you are intent on changing clothes you gotta go back to your room and do it there. it won't completely stop everyone but it'll dissuade people enough and also it'll add a tactical level where you gotta think what things am I gonna do today and what clothes would help with that

This post was inspired by: /u/[Quant0m133]

Boolean Search: ["cosmic microwave background" "kolmogorov complexity" "vacuum" "instanton" "de-sitter" "arxiv"]

Prerequisites:

1. The Cosmic Microwave Background is the relic electromagnetic radiation left over from the earlier stages of the hot Big Bang
2. The Kolmogorov Complexity deals with the complexity of objects and defines it as the size of the shortest binary program capable of the object's generation. The concept of "the shortest program" was developed by Andrey Kolmogorov while working on Turing Machines, random objects, and inductive inference. Kolmogorov.
3. In quantum field theory, the quantum vacuum state is the quantum state with the lowest possible energy. Generally, it contains no physical particles. The Zero-point field is sometimes used as a synonym for the vacuum state of an individual quantized field.
4. And Instanton was a term coined by Gerard t'Hooft. An instanton is a classical solution to equations of motion with a finite, non-zero action, either in quantum mechanics or in quantum field theory. An Instanton is a Euclidian Gauge Soliton (a soliton is a quantum or quasiparticle propagated as a traveling nondissipative wave that is neither preceded nor followed by another such disturbance). The non-perturbative part of gluons can be replaced by instantons.
5. In mathematical physics, n-dimensional de Sitter space is a maximally symmetric Lorentzian manifold with constant positive scalar curvature.

Computational complexity of the landscape II - Cosmological considerations by: Frederik Denef, Michael R. Douglas, Brian Greene, Claire Zukowski

We propose a new approach for multiverse analysis based on computational complexity, which leads to a new family of "computational" measure factors. By defining a cosmology as a space-time containing a vacuum with specified properties (for example small cosmological constant) together with rules for how time evolution will produce the vacuum, we can associate global time in a multiverse with clock time on a supercomputer that simulates it.

We argue for a principle of "limited computational complexity" governing early universe dynamics as simulated by this supercomputer, which translates to a global measure for regulating the infinities of eternal inflation. The rules for time evolu

I feel like Danielle and the countess Luann are birds of the feather and that Danielle is what Luann could have been if her life took a couple different turns. Have we ever seen them in the same room? Am I just high?

I am beginning to wonder if many more people (i know not everyone ) have these thoughts associated with derealization and hyper realizations like"wow what the fuck Im alive", "how is there anything at all", "is there a god", etc. but they don't have the extreme uncomfortable feelings associated with derealization? but it just seems like the only way to react is with a strong sense of fear at first but maybe that's just cuz I have anxiety? and others are just ok with it? but that just doesn't make sense to me because this reality is kind of freaky like we don't know what's going we don't know anything we are just stuck in these bodies. How do people not deeply question life? A hypothesis I had is that people who aren't freaked out just aren't as aware of us who derealize, like it is a different understanding. It feels like we are almost just more aware of the universe and reality than others. would love to hear some inputs on this topic.

I(28f) have a large dog. She's almost 70 pounds and a mix of herding breeds with something bigger. Usually if I have to go somewhere and can't bring her, there's a dog boarding facility we like that we bring her to.

I had to leave for a week or so and wasn't able to get a spot there because it was such late notice. I looked around for dog sitters and there was one that seemed relatively good, she had mostly good reviews, and when I talked to her she seemed to know what she was doing. She had another dog that my dog got along with very well, and she seemed like a good choice.

Until on the second day I was gone(Wednesday), she sent me a picture of my dog, who she was allowing her 6 year old niece to lie on. Like my dog was sleeping and her head was on my dogs side. I texted her asking wtf she was doing and she said that her niece loves the dog and she is very good with her and my dog “loves” her niece.

I asked her please not to let her niece do that, and she said that she had the right to make the decisions she thought were the right ones.

I told her that I was cancelling the rest of the stay and drove home to pick up my dog. I was able to find someone else to take her, who I know will not be unsafe.

I left a bad review on her page. It was a one star review explaining what happened and saying that she was unsafe and handled the situation in an unprofessional manner.

When I pulled up in her driveway she and her niece were sitting on their porch, with my dog not on a leash. She ran towards me when she saw my car and the sitter made no attempt to stop my dog from running towards the road.

I grabbed her and put her on a leash, and went up to their porch to pay her for the two days. When I gave her the money she was very rude. She said it was rude to cancel a stay during the stay itself, and that I was trying to ruin her business by making a big deal and leaving a bad review. She said it was common for people to let their kids around dogs and I shouldn't have a dog I wouldn't want around children.

I left so I didn't say anything I regretted and edited my review.

When I got back to where I was staying, not until almost 11 because I had to drop the dog off and drive all the way back, she had texted me asking me to remove the review and pay her for the rest of the days. I told her I wasn't removing an honest review but I'd pay her for the rest of the days when I got back.

She started cussing me out and then posted on social media about her “horr

Preamble

/r/explainlikeimfive is a bit of a strange case. The premise of the subreddit is legitimate enough; a place where people can ask questions without getting judged and receive super-oversimplified explanations. It acts as a more "soft" and "quick" alternative to /r/askscience, and while I would personally avoid consulting popular, vague subreddits for advice on anything (looking at you, /r/legaladvice and /r/relationshipadvice), it occupies a genuine niche.

First, let me make clear: This post is not a criticism of any of the questions asked. Asking questions is good and should be encouraged! This post is pointing out the bad mathematics in some of the answers. Moreover, I'm not criticizing answers for being too simplified; I mean, the whole point of ELI5 is to get a hyper-simplified, maybe slightly rough-around-the-edges explanation. This post will be focused only on answers that are blatantly erroneous, incredibly misleading, and don't "simplify" so much as "confuse".

A final note: I don't browse /r/explainlikeimfive regularly, so I'm not intending for this to be a commentary on the state of the subreddit or on its moderation team or whatever. Perhaps the moderators respond to reports of bad answers promptly and cleanly; I wouldn't know. This post is highly cherrypicked for entertainment purposes, and I admittedly jump to conclusions far faster than a responsible commentary should... though I think it's safe to advise against consulting /r/explainlikeimfive for any explanations where accuracy is paramount.

The dangers of Wikipedia

Let's start off soft with this thread. In a post about why 0! = 1 (where it turns out the OP doesn't even know what a factorial is), a user hints at the empty product justification for this identity:

> When you add numbers the "do nothing" number is 0. [...] With multiplication the "do nothing" number is not 0, it is 1.

This is a completely valid explanation. It's closely related to the explanation I'd give; that is, that the defining identity of the factorial is n! = (n-1)!n. There is nothing wrong with this answer; the problem is with the response:

> This is a wrong and bad explanation

This reply, of course, clarifies nothing. Our assailant later expands on this with the following posts:

> 0! is not multiplying no numbers together, your whole

Has anyone noticed an influx of unvaccinated caregivers who recently left a job and are getting back into childcare? Looking for someone now and it seems like a lot of people have recently left a job and are unvaccinated, I don’t know if it’s related but thought it might be odd. Mind you I’ve never gone looking for a nanny before.

I (28M) am the single father of two girls (3F and 8F). I used to use my parents as sitters but in time realized they refuse to follow my rules. They don’t enforce their bedtime, let them have junk food for dinner, even if I leave a healthy meal prepared that all they have to do is heat up. They baby the hell out of my kids, carrying my 3 year old everywhere, still trying to spoon feed both girls, etc. I found a great sitter for the rare times I’m out and the girls love her.

Recently, however, I got hung up at work and my sitter couldn’t relieve the nanny before a certain time nor could my nanny stay later. I begrudgingly called my parents and asked them to, explaining it was just for an hour. The sitter would come after that. They said okay. I went to a bachelor party straight from work and got home pretty late.

My parents were still there. They informed they sent the sitter home. My girls were still up at midnight, wired on junk food and my mom had given my 3 year old a bottle, when she hasn’t had one in over a year. I tried to keep my cool, sent my parents away and put my girls to bed.

I have no family outside them. I know cutting them off means I’ll be on my own. Am I insane for being okay with that?

3 absolute bangers of albums I grew up with and have been searching for recently since I've gotten into record collecting. All records are for personal use and will definitely not be resold.

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For cosmology that works in Anti de Sitter spaces see for example:

https://doi.org/10.1088/0034-4885/67/12/R02

https://doi.org/10.1088/1361-6382/ac27ee