How Much Of The Universe Can Humanity Ever See?

Props to the camera man for going that far just to get the footage.

Kudos for the team involved in doing this animations. They REALLY help understanding these advanced topics

This was the BEST explanation of the subject I've ever seen! I understand the principles but had difficulty conceptualizing the 'edges' of the universe. It will take a few rewatches and lots of pausing, but I'm certain I will finally wrap my head around this. Thank you!

PBS Space Time is the best! I always struggled to grasp the idea behind diagrams for each of this horizons and hoped that someone will make a video explaining it and there is no surprise that Matt did it. I will still need to watch this episode again to be able to understand it fully but it is great to have this video.

Great episode! Very well explained, and a spacetime diagram that Georgia O'Keeffe would be proud of. Thank you, Matt.

This is one of the best episodes, describing the basic concepts and definitions leading to a better understanding of time and expansion and the CMB that I've seen in a while. Good Job.

What a magnificent episode. And that's saying a lot, all of your videos are incredibly good.

Not only I am impressed by how much new information on a topic I thought I grasped I learned from this episode, the way it was presented was absolutely beautiful. I greatly appreciate the effort spent on making this episode. Give the person responsible for the graphs a raise!

This is one of my favorite episodes.I have never fully understood how we can map the CMB but there are objects whose light has not yet had time to reach us. 🤩 This makes so much sense now. Thanks!

I loved this episode!!! So beautiful and eloquently explained to someone familiar with some of the concepts here (space-time diagram for example) but then going further and expanding on those concepts to explore some of the largest meta-questions in cosmology; How much of the Universe will we ever see? When will the Universe past the Local Group start to recede away? and many other questions on the same topic. So excited to watch the next episode of Space Time!

This one wound up being a lot more complicated than I was expecting 😅. I'm very much looking forward to the next episode! Thank you for another informative episode and the super helpful charts!
God be with you out there everybody. ✝️ :)

I love that you're wearing a shirt that says, "Heat Death is Coming" while talking about the expansion of the observable universe.
We appreciate the little things as well

I absolutely love these videos deep diving on conformal mappings! It's such a powerful tool in GR.

Completely awesome episode. I was actually waiting for something like that for quite some time, even commented a couple of times here or at Sabine Hossenfelder's channel. Physics Girl also has a nice episode on it where she explains it with stones on a beach^^ Anyway, the animations were really well done and helpful and the video contains everything I ever hoped for.. And the best thing is: There is a second part!

I've always been confused about how space time diagrams and light cones worked until now. Phenomenal animation and explanation. 🤓

I'll be re-watching this one a few times to understand all of the nuances. Great episode!

I've always struggled to visualize how the light from the CMB reaches us, this is an amazing video. Thank you for making these

I loved that shell analogy and spacetime diagram; it was very intuitive. I am happy I got to live at a time where there are still stars and galaxies in the sky.

Always a great day when a new Space Time episode is released!

As you told me to imagine being a photon spat out by a star near the beginning of time, racing towards the Milky Way against expanding spacetime, I could feel myself red shifting across the decelerating horizon. Thank you for that superb imagery!

What a fantastic mind bending episode! Thank you!

Thank you for FINALLY providing an explanation of where the CMB comes from and how it relates to the size and geometry of the universe. I have seen the CMB invoked so many times without a real explanation other than "it comes from the big bang"

What an amazing video, the visuals really clarified a lot of things that I was foggy on when it came to this topic, thanks a lot!

it’s tragic yet strangely beautiful at the same time, that we can never discover everything. There will always be places to see and new things to discover. We will never get to see them all, but we will also never run out of new discoveries. We will always be explorers to the very end.

How many time can we rediscover the spacetime diagram ? It'll always blow my mind !
Quick edit : this is how to science vulgarization works. I'm not a fan of math, never been easy. Yet, from particules interaction, to the physics of black holes, expansion, dark matter/energy, geodesics ... We've learned a lot of complicated ways to represent GR to quantum mechanics, it's awesome ! Thanks Matt and your team

I don't think I've ever actually heard a clear description of the particle horizon until now. Awesome!

Fantastic episode, the animation and graphics helped me understand the material. Thanks PBS Space Time!

This stuff is great. Can't express how much I love this.

Amazing episode. It's insane to think about far far future milky way life having no way to know the things we know now, such as proving thr big bang via the CMB.
I wonder how a last billion year observation of light outside our local bubble would look like. Probably safe to imagine a starry sky with all stars slowly dissapearing?

you do such a good job please never quit making these

Douglas Adams quotes will win my heart every time ❤️

Matt always finds a creative & unique phrase to end each video with “Space Time” ☺️👍

This is an excellent video, absolutely love the topic and presentation! Thank you!

Fantastic episode, your diagrams and instruction really helped we non Astro PhD types. Thank You !

I actually thoroughly enjoyed the explanation of it all and I understood nearly all of it and it amazes me how us Bipedal apes that somehow are aware of our own existence is able to witness and understand things like this in some form. No matter if it's how things work or don't. It's still amazing that life exists as it does.
❤️🐦🥚🐣🐥🐤🐦❤️

This video was made for me! I have been drawing these things I called light leaves with the same teardrop shape and then someone pointed me to the Davis and Lineweaver paper and it explained everything but I understand it a lot better after watching this video!

Great mind-expanding video, Matt!

Love it that you also use These cool tranforming graphics on this topic, not seen like this before 😎

This really helped explain the comoving diagram, thanks! One flaw in the photon traveling video; I couldn’t figure out what I was confused by until I held a pencil in front of my screen and moved my phone so the photon stayed in place while the rest of the diagram moved. The Milky Way moves away from the photon at first, but starts moving back towards the photon after the pause at the 2X sphere. I know you care about accurate representation! For next week’s video, I would like to see this video redone without the pause and nail the expansion accurately. Also please be consistent with the photon being represented at the center of the wave packet. Then show a split screen, top, middle and bottom, where in each, the Milky Way is held in place, the photon is held in place, and the original galaxy is held in place, respectively. Thanks!

I'm kind of curious to know if it would be possible for the CMB to fit in with with one of the latest theories that our universe is in a black hole...

I like the background sound/effect/music that comes in when Matt starts the epic explanations.

Really unique way of representation through layers. 👍

Loved the animation as well. As for your question about our limits…how much does it matter? Old light from a young universe? Well put.

Thanks for this. I had been thinking about it. The transforming diagrams were incredible.

Thanx to Dr. Dowd for these videos... I know they are difficult to put together but they are excellent!

Always enlightening and elucidating, and fortunately with such light whose photons are reassuringly within the Hubble Horizon. Thanks for a great presentation of the cosmos!

Idk if it’s my headache, but this is the first video in a while that I struggle to understand the material. That is GREAT NEWS, I love learning new stuff! Great video!!

This seems to be the clearest explanation I've ever seen. Would have liked a summary at the end of the sizes of all horizons defined, though.

The animation makes it so much easier to grasp the concepts and ideas! Thank you!!!

I like to think I know something about the universe. I like it more when Space Time proves me wrong, and I have to watch again to try figure it all out. Definatly something new and mind bending.

I can't say I understood everything said in this video but it was fascinating all the same!! I hope that one day,when my mind has expanded along with my consciousness, I'll be able to intuitively comprehend every aspect of the world around me.

Beautiful video Matt; in my opinion one of the best of your great channel. I had to watch it twice.

Loved the hitchhiker reference. Well explained as always.

Thanks, Ive been waiting for this. It made sense that the cmb was both super far away yet fairly close depending on how you look at it.

I always feel like there's some fundamental flaw in the way space/time expands. It would seem we would be limited to what we can see of the observable universe, with every second being a more narrow cone of vision. Further, so much should have already passed us, leaving a big blank abyss.

While watching this video, I realized that space and time really are the same thing. When we look into the sky, we are looking into the past just as much, if not more than, we are looking at a far-off object.
It just never truly occured to me that at night we are looking into the distant past
I knew the light we were seeing was old but it still felt like I was looking at an object that was far away. But that's actually a weird way to think about light that is depicting phenomena that may not even exist anymore, especially as the space continuously changes.
I was just so used to "oh, the far off stars! Maybe someday we will explore them, like distant mountains!" But no, they are so unfathomably far away that we cannot experience them as we are now. And it seemed like the past was just a concept, an artifact of memory, and the only thing that really existed was the present.
But my whole life I could physically look into the past from the light of other stars as soon as my planet shielded the light of the star nearby. Every dozen hours we have the chance to look into far distant times.
Wild.

Outstanding job, as usual. Many thanks

"You could imagine the night sky as a set of shells" So the geocentrics and their heavenly spheres weren't entirely wrong, funky! I love when coincidences/connections like this happen

thank you so much, i've been thinking about exactly this for years and you answered all my questions :)

I could feel my mind expand and contract with the shape of that space-time diagram 😶‍🌫️🤯
Seriously, thank you for providing some amazing visual representation and narration.

Very interesting! Thank you for the lesson! :)

Really hard for me to follow and grasp.. but I trust you know what you're talking about Matt! :D I'm glad it makes sense to you lol

Can you please do a video on if there is any relationship between the Bekenstein Bound and Shannon Entropy? Like if I throw a 1kg book into a black hole, does the bound grow more than if I threw a 1kg chunk of iron?

I still find it rad that we only need around 50 digits of pi to calculate the circumference of the currently observable universe to within the accuracy of a single proton.

Amazing episode, it is as much beautiful as it is soul-crushing x-x

One of the most interesting video you did! Really loved it

This is in the top 3 of the best PBS Space Time Episodes!

The first time I heard of space being able to expand faster than light was from the children’s book series “Do you want to be a Wizard” by Diane Duane.

06:36 - I think you're right when saying DE "took over" at a certain point, billions of years ago. I think it likely started right at the beginning, but its effects only started to 'dominate' later on. If it didn't exist at the beginning, the Universe would've collapsed back in on itself and we wouldn't be here. You can see how the rate of change of the curve starts from right at the beginning - Dark Energy (expansion) must've therefore been having an effect, albeit a weaker effect earlier on.
My hypothesis is that spacetime (whatever it's made out of) is a substance, and that substance is entering our universe at all locations simultaneously. The more spacetime we have in our universe, the more "space" and "time" there is for new spacetime to enter from outside, so it gradually accelerates in expansion. Probably wrong, though! Just some thoughts about the multidimensional realm in which we exist. I'd love to see someone with expertise to try to figure out my hypothesis on a mathematical level, though. Perhaps someone already has. I mean, every other idea I've had, I've found out some great mind had the idea decades/centuries ago! Ideas are timeless.

Matt, your episodes are always… brilliant! And I always come away from them, or out of them, feeling smarter, a good-feeling illusion! But this time, this once, I must say I lost my footing! My head went spinning and I went reeling. Boy, I’ll need to read up on the (new to me) concepts you introduce here, and then re-watch and re-re-watch this video until the moving coordinates and shifting and stretching spacetime eventually sink into my kilogram and a half of wet slushy mush that neuroscientists call the brain. You’re right: I had never seen those diagrams before. They’re fascinating. Thanks again for all the effort you put in making these videos a piece of art. Have you thought of getting GPT4 etc. to help you with them? 😉

Matt, what can you tell us about the war between time and space/time, as described in that other science documentary, Doctor Who?

Great episode as always and just mindboggling. But less mindboggling after I watched it. The spherical shells concept was great at explaining this.

"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." Great video :)

At 2:20 there is a typo: I says the CMB was emitted after 380,00 years, instead of 380,000. 🙂

A nature article titled "Double-slit time diffraction at optical frequencies" was published on 3/4... I am very curious on your opinion on this! :)

This video was right on the edge of my event horizon of understanding, and expanded it, thank you.

Loved This Video! Can’t wait for the next one on this topic

Can you cover how Starship could be used to save the earth from a asteroid and/or comet?

Thanks, this episode answers a question I have had for a long time. How long before we start loosing the ability to see things.

So jealous of the people who can comprehend all or most of the intricacies involved in this episode.

Is the series on the brain's creation of time over? I was hoping for a few more episodes on that one :)

I have been trying to visualize what this video did for months now. Even thought about going into coding for this purpose. GJ, PBS.

"I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." Thank you for the opening ❤

There is something strangely beautiful about this, something poetic.

everything I ever hoped for.. And the best thing is: There is a second part!

If light is quantized, why doesn't it begin to stutter as it reaches the edge of where we can see it?

Question! Do to the red shift/blue shift of light in the universe(or some other method), can we tell where the center of the universe is roughly? And if so, where are we in relation to it?

I made it almost 3 minutes before my brain turned to mush. That's a new record!

I definitely need to watch this video a few more times before I finally convince myself I cannot understand it.

That graph at 8:18 is trippy. As I oscillate my eyes through a range of different focuses, the vertical lines change from greenish to blueish to reddish when viewed on my TV.

more of a bachelor of arts type myself but space Karl Urban really makes this stuff easy to understand

"Where we're going we won't need speed limits" ☺️

7:40 the spacetime diagram that accounts for the expansion of space is SO COOL

I'm curious if AI will ever extrapolate new insights about our universe. Cosmology seems like one area where the I in AI, required would be too demanding for it but I'd like to know your thoughts and the collective reasoning out there on it.

Could we in principle create a pair of probes that use direct counterfactual quantum Zeno effect principles and maintain the entanglement such that we put one probe outside the black hole horizon or event horizon and put the other one in and measure what's inside of it?

I’m reminded of a well written video about the simultaneous agoraphobia of just how kind bogglingly big the universe is and the claustrophobia of not being able to explore all of it and being trapped by the speed of light.
It also talked about the paper clip maximizer game.

What do you think about toroidal universe with the huge black/white hole in its centre?

Being early to a PBS Space Time Clip-Share video is great, Quality content is always worth a watch.

This is your best episode. And that’s saying a lot.

2:24 This question itself and the answer is the best thing for me in this video, I'm so happy I found you :D