What Actually Expands In An Expanding Universe? 

Don't know if it's universe, but I expanded a LOT in this quarantine

Bucket list after corona times: 1. Going in outer space 2. Turning off Electromagnetic force

"You might think there's only one type of redshift. But in fact, there's three. But actually, there's one."

As an addition to explain the difference in observation, to greatly simplify. The redshift in light kind of works the same for sounds. When you hear the siren of an ambulance it sounds different when the ambulance is driving towards then when the ambulance is drives away from you. thats why you know it is moving towards you or away even if you don't see it. But the sound the ambulance makes is always the same, just perceived different

I'm happy that Derek is now uploading frequently.

Me when electromagnetic force disappear: Mr. Stark, I don't feel so good

I appreciate you, dearly. I've recently been going through old videos of people like Feynman and Sagan. They existed at a time when video technology was still...amorphous. We only have so much video of them, and they died so long ago. I know they would be proud of creators and educators like you who are carrying on their work. Thank you.

ive seen 2 explanations before this one, and this one is by far the clearest, most well-suited for the average joe to understand. thank you.

"Why's it red?" "Because spacetime is expanding between us at an accelerating rate"

Little girl: "Why is it red?" Derek's first thought: "It's red shifted!"

I swear the title changed from "are you expanding with the universe" to " what actually expands in an expansing universe" and i think the thumbnail changed too. It's refreshing watching old veritasium videos. This video is actually one of my favorite veritasium's video, i think i watched this video at least 6 times

No other content creator has the ability this guy has to be able to explain concepts to 14 year old me and then 6 years later help me understand another concept the day before a final year Undergrad Physics exam...different level

I'm not fat, i'm red shifted...

Joke time: A man appears in the court for breaking traffic signal. The man argues that the red traffic light appeared green to him due to Doppler effect. The judge accepts his argument, cancels the charge of jumping traffic signal and instead fines him for crossing speed limit.

Incredible video, thanks a lot for taking the time and making the effort to make this.

This is the best channel ever for your content I can only imagine how much research is required. Thanks a lot ❤️

1:13 "Are you expanding with the universe" Geez, I know I've gained _a little_ weight during quarantine, but still.

Veritasium: "Do You Expand With the Universe?" 90% of the comments: _self depricating fat jokes_ Me: Our creativity sure isn't expanding.

very interesting and thought provoking, makes me want to go learn physics to fully understand what I fully imagined just now.

I want tô thank all of you that work on this channel for explaining that question. The first time I heard about the expansion of the universe I wondered about us being expanded as well. I could't find the explanation for this anywhere until I seen this video. That question literally gave me insomnia in the day I thought about It, now I can sleep 😅

Lesson learned: Never go out in outer space without electromagnetic forces.

"The problem is if you give it a second thought" Me: Yes, that is the source of all my anxieties

I've always wondered this! Thanks for explaining in such a clear way, this video made me so excited to finally understand

This is wonderfully explained but awesome to take in - I will have to watch this many more times.

Me personally holding a degree of Masters in Physics, still this guy, with every video, brings out the attention to something which seemed to me very trivial in the first go but never gave a second thought, and blows my mind every single time. I don't know how Derek does it. Best youtube channel I've ever subscribed to.

Me: *about to go to sleep* RU-vid (Veritasium): 'Do You Expand With The Universe?' Me: _I don't need sleep, I need answers_

"Are you expanding with the universe?". *Looks at belly*. "Why yes, yes I am"

With videos this good I opt in to watch the ads for you. Thanks for the content

11:23 "Why's it red?" You're in a non-inertial frame of reference kid, where the earth's gravitational field is dominating your local space-time curvature. The camera is also recording.

Consistent uploads with quality wow how's that even possible

Sir you are awesome . I knewed about expansion and red shift but this video gave me a clear picture and visualisation . Iam a class 11th student and love Physics.

thank you for the amazing and high quality content of yours ... ♥♥♥

Did not understand a thing bit yes its all sound good to me

All these videos make me realize is that Einstein is the GOAT. this dude found ONE EQUATION that all this is based around??? WILD.

I had that question for years. Thanka for the explanation

You are such a compelling and charismatic speaker

This whole "you're currently accelerating because of gravity" thing is still kind of making my head explode. Also, you're killing it.

10:53 “Mr. Stark, I don’t feel so good”

This got nothing to do with the video but I just got an ad in this video for no man's sky with the song retreat retreat by 65 Days of static. Really made me happy to hear that song again.

I have some questions about the "big bang". (genuinely interested in answers, not to argue). 1. When we look at distant galaxies that we say are "further back in time" due to how far away they are, and then we are told that these distant universes are "older" meaning the light we receive from them took so long to get to us from there that we can literally see back in time to the big bang. How is it that we can apparently see back to the origins of the big bang? If everything is expanding outward, and space itself is expanding (carrying us with it) faster than the speed of light, how is light then able to reach us from back in time when the big bang happened? 2. It is said that the big bang didn't happen in a "location" in space, but then I hear the same people also say that everything was once contained at a single infinite "point" prior to the big bang and then "BANG" everything that was contained in that single point is now shooting through space at incredible speeds and even space itself is expanding outward... Why do physicists say everything was once contained in a "single point"? How is it possible for a "point" to exist if spacetime itself was contained within that point? 3. Why do physicists say that the distant galaxies we see are "old" in the sense that they represent a time closer to the origin of the big bang? I understand the concept that the light we see from distant galaxies takes a very very long time to reach us, which means the light we are seeing is what that galaxy was like when the light first started traveling toward us, but how does this mean that the "old" galaxy we see has anything to do with the origins of the big bang, and how could we possibly measure how close that is to the origins of the big bang? 4. If we are moving with space at a greater speed than light (because of space itself expanding) this means that there are galaxies moving away from us that we will never see because the light will never reach us unless we one day learn to fold space ourselves, so we can't measure how vast space is exactly. Heck, some say space is infinite. How could we ever possibly know the origins of the big bang if we can't measure space? 5. How could we possibly tell that "the universe" is expanding "outward" if we can't actually measure the size of the universe in its entirety? Is it not just as likely that space (if its finite) outside of our observable universe is trillions of times bigger than our current observable universe and as a whole isn't actually expanding outward, and what we see isn't the whole story? For example, I could observe the atmosphere here in Australia and I could theoretically (with enough data) predict how the weather is going to behave long into the future, but if my observations were confined to the atmosphere within/above(?) Australia only, and I could not observe the outside world, It is not possible to predict the weather long into the future because it is only a small part of what is happening on a larger scale. Is it possible that the expansion of our current observable universe is just a small part of what is actually happening on a much larger scale outside of what we can currently observe? Isn't it just as likely that galaxies outside of where we can currently observe could actually be expanding through space toward us, as the "Big Freeze" theory that we will just continue expanding outward and eventually just fade into darkness?

Proud of myself for understanding approximately 27% of what this video is talking about.

Veritasium: are you expanding with the universe? me after eating two entire bags of crisps: *i sure am*

Derek, this video was very important. Thank you!

Someone needs to build a really good special relativity simulator to show the visceral look and feel of these spacetime transformations. I want to see how a ship's appearance would change as it passes by at semi-luminal speeds. I want to see how the colors would shift, lengths would contract, and time would slow down from each observer's perspective. Could you get on that?

He's getting a lot of use out of that rocket.

"What would the freefalling observer see" the pavement, presumably.

Very well explained!!! Thanks a lot :)

Another superior explanation of a misconception that you do so well.

"It's all doppler?" "Always has been."

Oh man I have been wondering about this question for as long as I know everything expands

I learn so much from this channel!!

Another great video. Thank you for making such great content. Namaste x

I laughed at 5:35 I'm imagining a hospitalised student visited by his friend after sustaining various injuries from his free fall and the friend asks him "What colour was the photon?" to which he responds "Piss off, mate!".

Derek really deserves Recognition for not being afraid to experiment in the Format of his Videos, he rather tries new things and tweaks his presentation with every project, not to mention the immense effort put into each video, it really shows!

I personally think the gravitation shift makes the most sense. Imagine a fog of non-luminescent celestial objects spanning the void of space each deforming the gravitation field around them like a little divot on an otherwise smooth piece of paper. As light travels through this torrential textured space time, it red shifts. This would also explain why objects more distant have a greater redshift than objects closer to us, which would otherwise make no sense.

This is a fantastic and accurate explanation. The only thing that is missing is explaining "g_00" the time time component of the metric tensor. Just looking at this component gives 99% of the predictions of General Relativity, as it reproduces Newtonian gravity. It's also the source of gravitational redshift, and it was worked out by Einstein in 1907-1909, long before the full theory.

In the difficult time of Corona, I am glad Derek provides us with videos more frequently. Life has become stagnant for me, and I feel like i'm getting dumber since there's so less to do and learn from during this time. These videos are a breath of relief for me and I really appreciate it. Thanks, Derek.

“When the universe was very young, it was so hot...” I'm going to stop you right there.

Love this channel…absolute crazy how I think crazy things and then hope somebody would have explained more or dig deeper and provide more insights And Bammmm…Verisatiun have video on it! Love❤️

long time viewer, thanks for the vast amounts of knowledge you brought to us during the years. This video confused me tho, i was under the assumption that dark energy (given enough time due to the fact that the expansion is accelerating) will eventually rip stars planets and even molecules apart. (ps. a video on dark energy will be very much appreciated :DD )

Probably, dunno honestly

D: Thanks for posting something I haven't seen repeated 1000 times on other pop-sci channels. This one was new to me.

I wish you discussed why we sometimes see blue-shift within the framework of an expanding Universe between all points. Also, if we would expand if we could turn off the electromagnetic and nuclear forces that hold everything together then it makes sense that if we could turn off the expansion/dark matter then everything should move closer together at least a little bit. We would get denser. Everything's density ideally is more than what we currently measure. The difference is therefore the strength of the effect of dark matter.

@Veritasium The only issue I have with this vid is that cosmologists in fact do NOT agree that the universe is homogeneous or isotropic. Since about 2013, with Planck Satellite data, scientists see that the universe strangely seems to "prefer" a direction. To add insult to injury, that direction aligns with our tiny earth and sun. Dr. Lior Shamir, just this month published about this in the paper "Large-Scale Asymmetry in the Distribution of Galaxy Spin Directions-Analysis and Reproduction."

5:30 - As I'm falling to my death, I'm going to be concerned with the color of a photon in a gravity tube.

Veritasium's animation team on another level. Along with the content, you guy are on a roll!! Thank you!

As usual, fantastic.

11:05 After watching this, I think the more accurate thing to say is molecules are expanding very slightly, instead of not at all.

Dude you're pumping out videos in these times like crazy. MAD respect.

This example helped me : You can tell the difference of sound made by a car moving towards you or getting away ; while the driver of the car hears the same pitch . If everyone tries to measure the wavelength ; It would be different . I still have a little problem relating this to universe level . ..but ...

It may make more sense to think of the universe as "unfolding" rather than expanding. This would give a structure for the early universe (a singularity just like a black hole), a reason for the big bang (the death of the singularity cause the event horizon to vanish and elastic spacetime to drastically flatten out), expansion (the gradual flattening after the initial explosive instant), the increasing nature of expansion (the rate at which any two points on an unfolding circle move apart is proportional to their starting distance; over longer distances of space or time points move apart more quickly), and may solve the problem of inconsistent measurements of the age of the universe if any methods would be affected by this model.

Maybe I'm missing something but I always wondered about that light Doppler effect. Sound Doppler is easy since speed of sound relative to the source changes, that's why sound waves infront of an object are compressed and behind it expanded, hence incoming source has higher frequency than outgoing one. E.g. sound doesn't move at the same speed relative to any inertial frame as light does. So what's the underlying mechanism of the Doppler effect when it comes to light when the light moves at the same speed relative to any inertial frame including its source of course? E.g. the observers should have no means to tell how fast the source of light moves relative to them right?

When the world needed him the most He became more frequent

what the hell! this man is making quality videos on almost weekly basis now. these videos are much better than documentaries on these topics! Keep up the great work!!

Best youtube channel... hands down.

The speed of light might not be constant but variable. Einstein initial idea was a variable speed of light. An idea he returned to in 1922. In 1957 Robert Dicke showed that the variable speed of light approach had equivalence with general relativity. Using the very same formula which reproduces the results of general relativity it predicts that light from distant galaxies has to be red shifted. The doppler explanation for redshift isn't the only one. There are others. At this point the expanding universe theory is anything but elegant. It requires far to many assumptions and ad hoc bolt on theories to explain the constant contradictions in the observations.

"Are you expanding with the universe?" Yes I am, sideways. Or maybe I eat too much...no definitely the Universe

"that tells you it's recording" "that's where you push the button again" are you training your kids to become your camera crew or what? still pretty cute though

I think the problem is that when we hear/talk about expanding space, we tend to think of space-time as sort of stretchy trampoline that can change shape, while (at least in my understanding) it's just that when you go at large enough scale where forces like gravity and dark energy are no longer dominant, things are getting further and further apart. The universe is expanding, spacetime isn't, but we misleadingly talk about "expanding space" like it's something flexible

باختصار ؛ الإنزياح الأحمر هو تأثير دوبلر ( والمثال الأشهر هو سيارة الإسعاف 🚑) Briefly ; The red shift is the Doppler effect (the most famous example is an ambulance 🚑)

I'm happy that Derek is uploading frequently. I'm unhappy that I can't grasp any of these .

Thank you for taking the time to explain very complex and interesting concepts!

I think i got it. Waves like sound and water wave, when put in a doppler effect scenario, will shift its speed and frequency, but with light, the speed does not shift because it is the same speed for all observer, but the frequency still does shifts.. I'd like to be corrected if I'm wrong

Derek can you help me understand a thought experiment I've had. If you look through a telescope at a planet very far away and can see the surface. Let's assume there is life on the planet and this telescope is powerful enough to see down to the street level so you can see people living their lives. Now this planet is 1000 light years away so you see the people as they were a 1000 years ago. Ok so far so good Now, suppose you take the telescope on a rocket and keep looking at the planet as you travel towards the planet at some very fast speed. Let's assume 0.5c. What I can't understand is this... Do the people as viewed through the telescope appear to move more quickly? I've had this thought experiment in my head for over 15 years and can't figure out what would happen. My instincts say the people should appear to move more quickly as you travel towards them but then this breaks the idea of relativity and light being the same speed no matter where you measure it. But then, if they move at the same speed as you travel towards them at some point you would reach the planet but through the telescope would still appear older and that's not true either. Maybe an idea for a video in the future?

The best part is the child asking "why is it red?" So coincidental. And convenient

The S over V ratio controls the nature of the structures that we see about us, whether they be cats or caterpillars or the cosmos. The key fact is that as an object changes in size, its surface area and its volume do not keep up with the change at the same pace. This has tremendous consequences. The surface area of a sphere of radius r is 4(pi)(r)(r), and its volume is (4/3)(pi)(r)(r)(r), and so its S over V ratio is 3/r. So, the smaller the object is, the more the object consists, like a piece of paper, almost entirely of surface. This is why biological cells are small: because that enables them to absorb nutrients more efficiently. In the case of a large object, like the sun, S/V is near zero, which means that it essentially has no surface. There is therefore next to nothing keeping the guts of the sun from spewing forth. The spewing forth of the guts of the sun is called sunlight. Next, consider a huge sphere of intergalactic space. Since space is a 'thing', this sphere is also one having an S over V ratio near zero (but a lot closer to 0 than the case of the sun), and so is also, like the sun, constantly spewing forth its guts. This is going on all over the cosmos, and accounts for the phenomenon naively referred to as the 'expanding universe' and the 'curvature of space'. In the vicinity of the sun it is strong enough to noticeably affect the orbit of the planet Mercury. The maximum speed of the spewing is known as the speed of light. In particular, photons have no independent motion. Like sticks floating along on the surface of a river, they are simply being carried along with this 'expansion' of the universe. The speed of light, then, isn't really about light.

ok, this is not easy to understand for people but I will try to show you... := means assigned a value for t:= 0 to 100 do (our time interval) Universal clock age of the universe. for k:= 0 to 100 do (our increasing or decreasing size) (gravity well) for j:= 0 to 100 do (where is it in its height) for i:= 0 to 100 do (which pixel is it in its width) for L:= 0 to 100 do (which pixel is it in depth) so now do what? So lets move the object sideways while it expands we have our coordinates x,y,z, we will say they all are starting at 0,0,0 front left top corner of our screen so x+i + some amount to move to the right m. Lets add blue shift and put the camera on the other side of the box. pixel(x+i+m,y+j,z+l) is equal to a color from a photo that will skin this box and we will add some blue on the right side and so for each L increment we are adding a bit of blue to r,g,b the pixel color. and we are removing a bit of red. Adding because the camera is on the other side of the box facing us. Does k matter? Will the box get larger when you look through the camera? No the camera is also getting larger. So why does it matter? Depending on how close to the sun or Jupiter it matters in the real world. So for each tick of t, we clear the screen, then we draw the box, we have to resize our skin photo(s) to fit the planes on the sides top bottom, while we transfer pixels from the photo to the right side we add the blue light gradient towards the camera. Can you see a situation where k matters? Of course. Light bends the closer to a massive object, the camera might be near jupiter the box near the sun. 3D no glasses a present for you since you are doing such a good job. No need to wear glasses adjust the pixel color. CGI can easily be 3D no glasses. See 3D no glasses chalk drawing on road blue cliff in road google images. So to answer your question, one universe big bang, one big bang, did all of it explode? Yes all on the same clock? Its your clock you are using doing your experiment. You just cleared the screen every t and took your measurements ipso facto all expanding at the same time. A ruler painted onto a balloon. t is a dimension because it will tick you cannot stop it. k is a dimension because it will expand you cannot stop it. j,i,L are 3 spacial dimensions.

I may not expand with universe but has expanded like never before in this lockdown.

Always, Derek always finds a relatable way of explaining things, and always takes an interesting topic, people like u r the real ppl quenching our curiosity

This one was deep. Congratulations!

Yes we are changing and that's why time Is non incremental and time and location is stored in each partical as it exspands. Compression sends particles back in time expansion sends them forwards in time it also changes their position from where they used to be to where they're going to be

10:54 I dont feel so good Mr Stark

10:53 - I don't feel so good Mr. Stark

Thank You!

I really enjoy your content 🙂❤️

Veritasium keeps making videos on questions I've wanted answers to but haven't had time to look deeply enough, great job! My suggestions for future topics: What are the cosmic requirements for life; What's the window for life in universes life span? Something about amino acids in space vs on earth vs theoretically possible ones... How would life appear to us/our equipment if we were to approach such planet at near lightspeed, could we theoretically see a timelapse of their history as we approach? How feasible would it be to build a forward "time capsule" on earth's orbit, a vessel that goes around earth at high % of speed of light and hosts a person? ...What's the opposite of lightspeed, i.e can something be truly static? Is difference between universe and not universe whether something "can be static"? Ok, I might've gotten carried away, but there's some good topics in there!

"And what about you? Are you expanding with the universe?" *me eating my 3rd box of pizza* I probably am

I need some space and time to consider this and expand my understanding

We do have tradition of practicing SOP's and used material as cover which is outer layer for our view.

Loving seeing more videos from Derek recently. The quality and quantity had increased, and I have no idea why but I love it.