What is outside of our known universe?

[CheeryFox 23,811]

2 hours ago, Pr0m4NV14 said:

Guys, what if life is a simulation?

There is some math and reasoning that points to the simulation hypothesis...but that's a hard pill to swallow. Still...not entirely far-fetched. I'ma say multiple universes and so forth. 

[Narcissus 352]

Beyond this universe is a hard chocolate coating. This is the creamy center, with a few nuts. 

[Midnight Solace 5,129]

I know that Equestria is somewhere out there...

[Kevin Tang 2,422]

A long time ago in a galaxy far,

far away.....                                   

NOTHING

(Why did I decided to post here? :/)

Edited December 6, 2018 by Kevin Tang

[Stinky Pinkie 39]

3 hours ago, Midnight Solace said:

I know that Equestria is somewhere out there...

It certainly is!

[Quantum Pony 40]

 

(Not really a cosmologist here but learned a thing or two over beers with some pals  )

To answer this question, we need to take a quick trip back in history  .

A few decades ago, astro people found something they couldn't explain - the temperature at different regions in the early universe is really really similar! They looked at the Cosmic Microwave Background (CMB) which is like a snapshot of the observable universe when it is around 380,000 years old. 

 [1]

The color denotes different temperature across different regions in the observable universe. Even though it doesn't look very homogenous, the temperature difference is really quite small. In fact, they are the same within an interval of 0.001 degree celcius. 

In special relativity, we know that information cannot travel faster than the speed of light. If I do something drastic like destroying the sun, Earth will feel no effect within 8 minutes as that is the time it takes for light to travel here. So cause and effect are not instantaneous but bounded by the speed of light. Similarly, any event within a radius of 300,000km can affect me over the course of one second. But if something is say 310,000km away, it will have no effect on me within one second. For those who are familiar, this describes the concept of a lightcone. 

Now back to the CMB. The time between the big bang and CMB is roughly 380,000 years. So it turns out (after some computation), if we print out the CMB picture above on an A4 paper and look at two points that are about 1cm apart, they are causally disconnected. That means, since the big bang, events that affect one point in the CMB can in no way affect the other point 1cm away (on the A4 paper). So then how can they have the same temperature o.O? It's like a random group of people going to a party but wearing the exact same shirt even though there is no communication of any sort between them!

So it is really unexpected that causally disconnected region on the CMB have the same temperature! This is known as the Horizon problem. 

The explanation is inflation. Basically, shortly after the Big Bang, spacetime itself is growing at an exponential rate (infact, they are expanding faster than the speed of light), so the small patches with evenly distributed temperature near the time of the Big Bang expands really really quickly, giving us the homogeneous state of the CMB. This is why even though the regions in CMB are causally disconnected, the temperature are the same as inflation stretches everything so quickly that it seems to violate relativity. Thus solving the Horizon problem.

So here is the punch line that answers the original question. Inflation shows us that spacetime near the beginning of the universe expands much faster than the observable universe. So one can argue that outside the observable universe today, there is still something as spacetime still exists which is much larger and ever growing. Although, I personally believe it is just empty space outside the observable universe lying happily in the fabric of spacetime. But we will never know since we can't ever see them . 

Throughout the eons, expansion of spacetime is no longer as fast as during inflation, but it is still happening and spacetime is still expanding. So I believe the current consensus is something like the picture below

[2]

However, spacetime would not be infinite (yet) but probably millions (10^30 according to some sources) times greater than the observable universe depending on the inflation model you are using. And beyond the boundary of space-time, well... who knows... It is a region without space nor time... . 

 

(side note: now that I finished writing it, I felt I could probably had just started with the punchline... but anyways, inflation is too cool a thing not to talk about )

References:

[1] WMAP Collaboration (2003) First-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: preliminary maps and basic results. Astrophysical Journal Supplement Series. 148 (1): 1–27. arXiv:astro-ph/0302207. 

[2] Hard Science (2014) What Lies Beyond the Edge of the Observable Universe?

https://futurism.com/what-lies-beyond-the-edge-of-the-observable-universe

On 8/25/2018 at 3:51 AM, Jokuc said:

Physicists of mlpf, correct me if I'm wrong, but if time moves faster the further away you are from mass and the universe isn't infinite, wouldn't that mean either a) time is instant at the border of the universe, meaning that it expands at infinite speed, meaning that it's all a paradox and the universe is indeed infinite or b) We should all scrap the concept of space and time and start thinking in spacetime, which would mean spacetime doesn't exist at the border of the universe or c) I'm an idiot?

That is an excellent and very tricky question. The idea is that time is relative and depends on the observer. Consider an experiment where scientist A stays near the horizon of a black hole (which is a very massive object) and scientist B stays further away. They each have a stop watch. 

Now, in general relativity, gravitational force is the result of the curvature of spacetime. So the stronger the curvature, the stronger the force. And mass is what curves spacetime. Since Scientist A is near the horizon of the blackhole, the curvature of spacetime is much stronger compared to scientist B. And general relativity tells us that the clock for scientist A ticks much slower than scientist B.

However, for an object like Earth, it is not very massive on a cosmic scale so we can pretty much approximate the spacetime near it as flat. At the boundary of the universe, there can still be planets, blackholes or just vacuum. If it is just vacuum, the curvature of spacetime is probably similar to Earth (as in being flat). So time would pass pretty much at the same pace for a scientist on Earth compared to a scientist in the vacuum at the boundary of the observable universe. 

Very roughly, the clock ticks 'fastest' in flat space and practically stops when you are near the horizon of a blackhole. 

Hope that helps  

[Jokuc 8,172]

On 12/22/2018 at 8:01 PM, Quantum Pony said:

So then how can they have the same temperature o.O? It's like a random group of people going to a party but wearing the exact same shirt even though there is no communication of any sort between them!

This reminds me of quantum entanglement. Einstein's theory that entangled particles are given properties based on predetermined conditions has been proven false. The theory that two particles can - on their own - communicate instantly, faster than the speed of light, seems really strange to me. I had this thought that if over 70% of the universe is what we call dark energy, it must have a purpose. Maybe it's one big blob of energy that senses everything that happens in the universe and somehow tells everything how to behave, like forcing an entangled particle to have the opposite property of the other. I have no idea what I'm talking about but spitting out stupid thoughts usually gives me the most interesting answers, lol.

[Celli 4,332]

@Quantum Pony

Speaking of Dark Flow, this a good video on the subject, I recommend giving it a watch.

 

[Quantum Pony 40]

7 hours ago, Jokuc said:

This reminds me of quantum entanglement. Einstein's theory that entangled particles are given properties based on predetermined conditions has been proven false. The theory that two particles can - on their own - communicate instantly, faster than the speed of light, seems really strange to me. I had this thought that if over 70% of the universe is what we call dark energy, it must have a purpose. Maybe it's one big blob of energy that senses everything that happens in the universe and somehow tells everything how to behave, like forcing an entangled particle to have the opposite property of the other. I have no idea what I'm talking about but spitting out stupid thoughts usually gives me the most interesting answers, lol.

Quantum entanglement is definitely strange.  In fact, when physicists talk about quantum mechanics as being strange they are not refering to its probabilistic nature nor a baseball tunneling through walls, they are refering to the strangeness in things such as entanglement  .  What you said does seem interesting and resonates with something said by Schrödinger : "Quantum physics thus reveals a basic onenes of the universe." 

Dark energy is mysterious as well. One of the current models is that dark energy is what actually drives inflation and the expansion of the universe  . 

 

6 hours ago, Celli said:

Speaking of Dark Flow, this a good video on the subject, I recommend giving it a watch.

Thank you for the video! . When I posted that figure I didn't really know what dark flow is... The video certainly does provide compelling evidence of its existence and perhaps there is something interesting lying outside the observable universe as well .

[Jokuc 8,172]

13 hours ago, Quantum Pony said:

Quantum entanglement

I just realized I'm watching an anime where they talk about quantum entanglement and other mysteries regarding quantum mechanics. I just watched the latest episode and they brought it up again, what are these weird coincidences...

[Treeglow Flicker 13,023]

Giant space dog! 20 bits says there's a giant space dog!

[Fluttershutter 2,118]

One thing that's hard to wrap your head around is that outside the universe there isn't time and space as we understand them. There might be some equivalent, anything anybody says is just a guess. Humans are an incredibly primitive species and we don't know much.

The idea that the observable universe is a simulation is being taken more and more seriously lately.

Edited December 28, 2018 by Fluttershutter

[Lucky Bolt 34,914]

What's outside of our universe you ask? Equestria! 

[The Historian 515]

That's why it's called the known universe. We're not sure what extends beyond the cosmic light horizon. Probably never actually will, but it's an interesting idea to contemplate.

[Olly 1,008]

this topic has been pretty thoroughly covered... not much I can add. But I think it would help for us not to think of the universe as we're tempted to-  that is, some kind of "bubble" of space expanding. Quantum physics complicates reality considerably, we should think of ourselves existing in different states of dimensions, observable and non-observable. Branes, quantum field, superstrings, all these theories are directly related to understanding reality and are very complicated and abstract. Rather than thinking of space as something that's expanding into something else, we should probably consider that reality might be very different, that what the universe is is just part of a larger dimensional apparatus that's best understood through mathematics and such... how can you really imagine other dimensions, any more than imagine colors no one has ever seen? 

 

Asking ourselves what's "outside" of the universe might be like asking an ant what's outside of the earth. First the ant would have to know what the "earth" is, what a planet is. Then it would have to know that there's space outside of it, and what space is, and how it came into existence and how it works. We're trying to understand something almost from behind a wall while being blindfolded. Not that it can't be done, but you see the difficulty.

Edited April 15, 2019 by Olly

[Nsxile 25,672]

No one truly knows tbh...

[MangoFoalix 24,898]

Anything, I guess. Who really knows what is outside there.