What Actually Expands In An Expanding Universe?

  • Am Vor year

    VeritasiumVeritasium

    As the universe expands, is said to "stretch" photons. But if it stretches photons, does it also stretch molecules, galaxies and you? A portion of this video was sponsored by Salesforce. Go to salesforce.com/veritasium to learn more.

    Special thanks to Geraint Lewis - this video was based on his paper "On the relativity of redshifts"
    arxiv.org/abs/1605.08634
    Check out his DE-film channel: ve42.co/gfl and books: ve42.co/GFLbooks

    References:
    Expanding Space: the Root of all Evil?
    Matthew J. Francis, Luke A. Barnes, J. Berian James, Geraint F. Lewis
    arxiv.org/abs/0707.0380

    Editing and VFX by Trenton Oliver
    Thumbnail by Ignat Berbeci

    Music from epidemicsound.com

LOL-4C554C
LOL-4C554C

Can we just appreciate how much quality content he's publishing in the last time. That's amazing!

Vor year
Secret Snow
Secret Snow

@CosmicAliveness Y

Vor 15 Tage
GOLVELLIUS
GOLVELLIUS

No.

Vor Monat
Educated Guest
Educated Guest

"Expansion" came not from Hubble himself, but from a catholic priest who misinterpreted Hubble observation. Expansion + Big Bang is Flat Earth mentality: Hubble observation was finally explained in "Cutting Edge with Bob Lazar" publication, that solved Vera Rubin puzzle about spiral galaxies and even dinosaur extinction.

Vor 2 Monate
Cachi -
Cachi -

Did he forget to mention objects move faster away from us, the farther they are from us? Am I correct in saying this? Anyone? Anyone? Bueller? Bueller?

Vor 4 Monate
Alexandre Kassiantchouk
Alexandre Kassiantchouk

Derek, astronomy is much simpler - could be explained to a kid: If 14B years ago you were mailing packages to yourself, one package every day; And now, when day is twice shorter than it used to be, you are receiving your parcels: you receive a parcel every other day only (no backlog and no losses)! Redshift is neither about light, nor space. It is about time change.

Vor 7 Monate
Grim Gearheart
Grim Gearheart

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.

Vor 2 Monate
ረቂቅ Rekik
ረቂቅ Rekik

Exactly👍👍

Vor Monat
Jeanpierre Perdomo
Jeanpierre Perdomo

U

Vor Monat
Lundy's Den
Lundy's Den

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.

Vor 2 Monate
Patrick Foley
Patrick Foley

Really great. I have a degree in physics and learned SO MUCH from this. Space is amazing.

Vor 7 Monate
Baymax
Baymax

hell yeah

Vor 5 Monate
Man in The Moon
Man in The Moon

Interesting. I've often wondered whether there's something for the Universe to expand into, and you stimulated the question again with your reference to Cosmic Fluid (CF): suppose you could make your way 'there' in the hope of studying the CF from the outside looking in, just precisely where would 'there' be?

Vor 9 Tage
Shubham Gupta
Shubham Gupta

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.

Vor year
Gary Halliday
Gary Halliday

@eric debord You and @Science Revolution guy should record a series of debates between yourselves for youtube. You'd make a lot money I'm sure.

Vor Monat
Tonio Kettner
Tonio Kettner

@Science Revolution you clearly have no idea and should stop talking so agressively

Vor year
Amaraticando
Amaraticando

@Science Revolution mandatory XKCD: https://xkcd.com/1342/

Vor year
Spark
Spark

@Daniel Martin TF did I do?

Vor year
Science Revolution
Science Revolution

@Daniel Martin You can't handle the truth.

Vor year
Benjamin Thomsen
Benjamin Thomsen

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

Vor Monat
ngbusca
ngbusca

This is an excellent video, it's crazy how even practicing cosmologists don't understand these concepts clearly

Vor 7 Monate
Blair Sadewitz
Blair Sadewitz

@Art Donovan I think he might have meant like, "Don't understand the ultimate reasons any of this happens" or something like that. Taken literally, it's an absurd statement, obviously. Perhaps I'm being too charitable.

Vor 2 Monate
Art Donovan
Art Donovan

If you're referring to cosmologists who work at universities, of course they understand these concepts! It's the general public that can get confused.

Vor 3 Monate
Drusix
Drusix

What are you talking about? How can you be cosmologist and not understand this? He said that this concept is commonly misunderstood but what he meant was that by average people not by cosmologists.

Vor 4 Monate
ALOYSIOUS DAVIS
ALOYSIOUS DAVIS

What is a practicing cosmologist?

Vor 4 Monate
Travus Faulkner
Travus Faulkner

Could something be redshifted because light photons traveling through a more empty vacuum of space would potentially increase its speed causing it to be red shift just because it is able to move quicker through that space. Potentially this thought process could be an argument against an expanding universe.

Vor 3 Monate
KillerSugar
KillerSugar

I love your videos, but the concepts in this one weren’t very well explained and I came away more confused... watched it twice too. Why is there a series of photons being passed along in series? I’m sure that’s an analogy, but I’m not sure for what. Why do the photons lose energy in a vacuum?Because they’re affected by gravity? Wouldn’t the accelerating rocket cause compression of the photon wave’s frequency and result in a violet-shift due to the Doppler effect? I’d love a longer follow up video on this topic.

Vor 7 Monate
Louis DROUARD
Louis DROUARD

@Beer_Dad well, he said it, "at this scale" the CMB is isotropic and homogeneous if you don't watch to closely. The scale factor is expanding.

Vor Monat
Beer_Dad
Beer_Dad

@Seeminglynn But there are structural variations in the CMB, so whilst the CMB is isotropic, the universe is not homogeneous - at least based on my understanding of the term - and thus we have the large scale structure - and every time we increase our observational scale, we find ever larger structures - so what exactly is expanding? Maybe it's just semantics and I'm not understanding his definition properly. I'm still lost unfortunately. Oh well I guess that's why I ended up pursuing computing instead of physics.

Vor 2 Monate
Seeminglynn
Seeminglynn

@Beer_Dad i think the basis for universe being homogeneous is the discovery of cosmic microwave background, which demonstrated that the universe is isotropic

Vor 2 Monate
Beer_Dad
Beer_Dad

He kinda lost me when he stated that the universe is homogenous - there is literally no evidence that this is the case - on every scale we have measured the universe has structure. He's kind of accepting existing subjective assumptions on anisotrophy, which don't currently have any observational evidence.

Vor 2 Monate
DEADPOOL 007
DEADPOOL 007

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

Vor year
Shikhar Tiwari
Shikhar Tiwari

Definitely it's the universe

Vor 27 Tage
ADAM HAGE
ADAM HAGE

🤣 🤣 🤣 🤣

Vor Monat
Banter Maestro2
Banter Maestro2

@Science Revolution You win the Dunning-Kruger Award for _Perceived Excellence in Science._ Congrats!

Vor Monat
Banter Maestro2
Banter Maestro2

I can sense the gravity of this situation from here.

Vor Monat
Dragon Rainbow
Dragon Rainbow

Good one

Vor Monat
Bohan Xu
Bohan Xu

7:28 I never quite understand this part. If the motion of earth is well-defined relatively to the cosmic background radiation, then does it mean that the universe has a preferred reference frame in terms of velocity? I understand that the law of physics is invariant under boost (of reference frame), but does the (initial) state of the universe have a special frame where net momentum is zero?... and that determines the doppler shift of CMB?

Vor Monat
Chris Allen
Chris Allen

This is an excellent question. We often say there is no preferred reference frame of the universe, even though the CMB seems to provide an excellent counter-point to that. The CMB is the furthest "object" that we can see back in time, and we can measure its Doppler shift via a special relativistic effect called beaming. Since we are moving at 600 km/s through space relative to the CMB, we see portion moving towards us as being blueshifted and beamed to a higher brightness, while the portion moving away from us is redshifted and similarly is dimmer. Based on the amount of beaming we see, we are able to determine our relative motion (to within some uncertainty of a few 10s of km/s). Because of this, it is somewhat fair to say that the observable universe does have a preferred reference frame in terms of velocity, however the universe itself still does not, as we still cannot define the CMB's relative motion to objects outside of the observable universe. Additionally, this preferred reference frame would be different depending on where in the universe you are, as our preferred reference frame (the observed CMB) would be much different than what someone at the other end of the universe 15 Gpc away would see as their microwave background radiation. The initial state of the universe did not have a special frame where the net momentum was zero. The universe was expanding back then just as it is now (even more so during the period of inflation), and as a result no such reference frame could exist as far as I know.

Vor Monat
Satyajit Prakash
Satyajit Prakash

Thank you very much for clarifying. I was very tense since I learned about a theory of end of our universe where it was said that all the atoms will decay due to the expansion.

Vor 5 Monate
Costas Blackgeorge
Costas Blackgeorge

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 )

Vor Monat
Owenbegowin
Owenbegowin

This isn’t particularly important, but if the cosmological fluid appears homogeneous and isotropic, wouldn’t it be impossible to see that it’s expanding? It would be like zooming in on a completely blank computer screen; you wouldn’t notice any change

Vor 8 Monate
Shruti K
Shruti K

@Henrique Sato 🤯

Vor 7 Monate
denis charette
denis charette

We notice the expansion because of the redshift of the light received from far away galaxies. We conclude that the density of matter of the universe decreases even if we cannot see it decrease in our lifetime.

Vor 7 Monate
Henrique Sato
Henrique Sato

It would become less dense, so you could notice some change. It looks the same in space, not in time.

Vor 7 Monate
Abhishek Thorat
Abhishek Thorat

I'm happy that Derek is now uploading frequently.

Vor year
Relaxing music... موسيقى هادئه
Relaxing music... موسيقى هادئه

The Quran We built the universe with ˹great˺ might, and We are certainly expanding ˹it˺. And the heaven We constructed with strength,and indeed, We are [its] expander. Adh-Dhariyat Sura 47

Vor 11 Monate
Science Revolution
Science Revolution

Time Dilation IS BS If you travel at 3 x 10^8 m/s speed to the nearest star and back, it will take 8 years. The earth simultaneously moves around the sun 8 times, people on earth are 8 years older. What is time dilation? Time has no physical existence. Your clock rate changed due to any conditions that have nothing to do with time.

Vor year
Science Revolution
Science Revolution

The Scientific Lie Of The Ocean Tide All scientists think the tide is caused by the moon's and sun's gravity. All textbooks say so. But the fact is not. Tide is impossible to be caused by the moon's and sun's gravity. Why? If you put some water in the space between the earth and the moon, what will happen? The water will accelerate at the net force direction until it hits the earth or the moon depend on their distance. Saying tide is caused by the moon's gravity is absurd, fully demonstrated how confused theoretical physicists are. They can't even think rationally. F=ma, the net force direction is always the acceleration direction. If the moon's gravity is causing ocean tide, it must be stronger than the earth's gravity at sea level. Why tide is not caused by the sun's or moon's gravity? How much net force is acting on seawater? Which direction? All matters are governed by gravity. Stronger gravity dominates all matters motions. Matters on earth are governed by earth's gravity only. If the sun's gravity can affect matters on earth, then day time the sea level will be higher, the daylight side atmosphere will be higher. Summertime tide will be higher than the Wintertime tide. From common sense, if the tide is caused by the sun's or moon's gravity, then the highest tide should be under the solar eclipse path. There should be two high tides move around the earth near the equator every day, one high tide follows the overhead sun and one high tide follows the overhead moon. Near the poles should be all low tides. High tides should be moving around the earth from east to west not locally up and down. If high tide is moving around the earth at 1000 miles per hour near the equator, can ships get a free ride? If high tide is not moving around the earth, the present tide theory is not correct. Sun's attraction force s equal to the earth's centrifugal force, therefore stable orbit. The net force between earth and moon is zero, all masses only accelerate at net force direction. Sun's and moon's gravity are impossible to cause tide. Scientists should seek out the true mechanism. Don't be a frog at the bottom of the well made by controlled mainstream science.

Vor year
SKP
SKP

Hi abhishek sir🙏🏻 Sir mai aapka bada wala hoon sir

Vor year
Stop the Philosophical Zombies
Stop the Philosophical Zombies

In your mom.

Vor year
G Avila
G Avila

WOW!!! That is such a great explanation!!! Thank you so much for so much you do for us!!! May Life preserve you with, and for us, for a very long time in a perfectly healthy maner. 🙏🏾🙏🏾🙏🏾

Vor 7 Monate
Eugene le Roux
Eugene le Roux

Thank you for an informative and great presentation.

Vor 7 Monate
James Kleffel
James Kleffel

Finally!!! Thank you! This is exactly what i have been wondering for years and years dude. Absolutely always wondered if everything is expanding. Like, everything. I figured you wouldn’t be able to tell because the space between absolutely everything would be getting larger… inso perception would also expand.

Vor 7 Monate
Ken Koskinen
Ken Koskinen

I claim the cells of spacetime exist and do expand in the mostly empty voids. This is where cosmic expansion occurs. Therefore things that aren't gravitational ly and/or electromagnetically bound will expand along with the growing cells of spacetime. This, of course, is comparative to analogous things within galaxies (no cosmic expansion occurs there).

Vor 7 Monate
Vinay Kumar
Vinay Kumar

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

Vor year
Burgo
Burgo

@Chax Reports doesn’t change the fact they are too weak on the scale of our body

Vor 8 Monate
Chax Reports
Chax Reports

@Burgo There are even weaker forces... It is all relative thing... if EM forces are not at work it is the gravitational forces that will dominate. So seriously there is nothing to laugh about.

Vor 8 Monate
Burgo
Burgo

@Chax Reports do you realise how weak gravitational forces are? Lmao

Vor 8 Monate
Chax Reports
Chax Reports

Even if you don't have electromagnetic forces you'll be still held together by gravitational forces.

Vor 9 Monate
Ole Rasmussen
Ole Rasmussen

"Don't forget your fundamental forces when you go outside" - Moms everywhere

Vor 11 Monate
BWMPublic
BWMPublic

Is it possible for visible light to red-shift all the way down into radio waves?

Vor 7 Monate
Pritam Roy
Pritam Roy

Being a cosmology student, i really appreciate the content of this video, very much enlighten

Vor 7 Monate
Doug Loggie
Doug Loggie

Well...I really enjoy expanding my brain cells around these videos but I have a question about light photons travelling as both particles and as a wave form...the mental imagery of a wave is of a rolling flat form of moving material with peaks and troughs...but it is on a flat plane...my question applies to radio waves and sound waves too...the concept is confusing...anyway, I really love your work...cheers

Vor Monat
Dave Humphreys
Dave Humphreys

Thanks for the video. Now, the rate of expansion of the universe is accelerating. If this doesn't stop, then I've heard that eventually, even the spaces between the electrons and nuclei of atoms, then between the quarks in the protons and neutrons, WILL start to expand in what cosmologists call the Big Rip. Is this still the current thinking, or has this been disproved?

Vor 7 Monate
Philipp Velimirovic
Philipp Velimirovic

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!

Vor year
Vigilant Cosmic Penguin
Vigilant Cosmic Penguin

He's really done a good job of making sure he doesn't get pigeonholed into a specific type of video.

Vor year
Liam Roche
Liam Roche

I have often thought along similar lines to the end of this video and completely agree with the series of points and intuitive interpretations made, and with almost all of the presentation at the start. However, there is a problem with the description of the falling man 5:23. First, if he starts falling at the top, the colour he sees is the colour the photon ends up, which is red, say (the video said "blue"). And at the bottom he is moving fast in the opposite direction to the photon. The Doppler effect (referred to in the video) is dependent on direction - if he ran into the photon low down the tower it would be bluer for two reasons - his velocity and gravitational blueshift. So that's not the right reasoning - the colours at the top and the bottom don't agree. Of course it would be the relativistic Doppler effect if anything (because that's the relevant physics) but this is still a direction-dependent effect that is opposite to what we are looking for. As he falls, the relativistic Doppler effect would blueshift photons that are already more energetic because of being lower in the gravitational field (as observed by building dwellers), so this is not what we want! What works to make the photons look the same colour at all heights is the special relativistic time dilation, gamma. Let's check this. The gravitational redshift is to first order a factor of (1 + gh/c^2), where h is the height below the top of the tower, our chosen reference (which happens to be where the falling man is stationary) The velocity of the falling man is sqrt(2gh), so gamma is 1 / sqrt(1 - 2gh/c^2) at any distance below the top, which is to an excellent approximation (1 + gh/c^2). Thus this factor applied to the frequencies observed by observers in the building makes the photons the same shade of red as they were at the top of the tower. QED ;)

Vor 7 Monate
Liam Roche
Liam Roche

@Jonas Larsson What do you mean? If a photon starts in a gravitational field (eg surface of Earth) and ends outside it (eg point far away in space stationary relative to the Earth), it is certainly red-shifted.

Vor 9 Tage
Jonas Larsson
Jonas Larsson

Nah this can't be right. The falling man is in an inertial frame. It would be the same as sending a photon outside of a gravitational field, which is not red-shifted.

Vor 9 Tage
Amit Kumar
Amit Kumar

If his reasoning was right then i guess you are wrong. It should be blue all the time for the falling man. Compare it to light in space craft and a man watching it from outside.

Vor 2 Monate
Gamer Chair
Gamer Chair

Agreed. Thank you for your interpretation sir.

Vor 6 Monate
R Wester
R Wester

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

Vor 29 Tage
Kashmiri Nomad
Kashmiri Nomad

Love your videos. Always teaching me something new and interesting. Thank you!

Vor 7 Monate
Daniel Bond
Daniel Bond

Imagine: the cosmic fluid is expanding. That expansion is starting in every point, everywhere, at every moment. That expansion creates drag against the mass. The perception of distance would appear to expand between any set of masses for all time. This is what’s happening. Time is expanding uniformly in all directions in an analog fashion. Mass creates drag against time (gravity) and as time proceeds, the rate that we are pushed away by that drag will increase.

Vor Monat
Mike Mondano
Mike Mondano

Time is not a thing. It is like color, an emergent. It may be wholly subjective. Even Einstein wondered about that.

Vor Monat
jack kelly
jack kelly

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

Vor year
saswat meher
saswat meher

Also they got time for multiple thumbnails...

Vor year
Richard Scritchfield
Richard Scritchfield

Best explanation I have ever heard! Great work!

Vor Monat
Jared Heiner
Jared Heiner

Wouldn’t this logically mean that from a specific frame of reference time would be nearly infinite if measured as a rate of change?

Vor Monat
crutchgecko
crutchgecko

Thats right. At keast in my humble opinion. Time basically stops inside a black hole. I wonder then if light eminating from near a black hole is also red shifted? The photos we have from black holes look rather orangy so maybe im on to something? Likewise time 'speeds up' in empty space. Time also slows down depending on your velocity so apparently if it takes you 4.5 years to reach the nearest star but you travel at 90% the speed of light you may only age 2.35 years, and an atomic clock travelling with you would agree.

Vor Monat
Frei Denker
Frei Denker

I suggest reading the book "The Static Universe - Exploding the Myth of Cosmic Expansion" by Dr. Hilton Ratcliffe. It's available on Amazon. He questions cosmic expansion on the basis of very good science.

Vor 2 Monate
TheAdrenalineJunky
TheAdrenalineJunky

Hmmm is it possible the universe is expanding due to moving through a 4th dimension ? Imagine having a cup of water, where manipulating the cup changes the form of the contents. Now instead of forces acting on the cup, our universe is changing shape as we move through different slices of the “4d cup” in 3D space. Are there any rules that the universe has to expand? Can it ever contract or not change for periods of time ?

Vor 26 Tage
Yumiko
Yumiko

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

Vor year
kinnlmk
kinnlmk

@Lakshay - Musical Scientist Considering space as a fabric is helpful, but it limits understanding. It is a manifold of at least 3 dimensions. Spacetime is often considered a 4D manifold. The volume of the universe is increasing, but the volume of matter is pretty much static in comparison, for now. There are gravity waves that affect matter, but the net result is pretty much zero. It is believed that the volume of the universe will become so large it will overcome the fundamental forces, and all matter will break down to its quintessential components or into a form beyond our current understanding.

Vor 2 Monate
Lakshay - Musical Scientist
Lakshay - Musical Scientist

@kinnlmk exactly, but is the space fabric is what is expanding or the planets itself ?

Vor 2 Monate
kinnlmk
kinnlmk

@Lakshay - Musical Scientist ​It is expanding faster than the speed of light and getting faster. If it expanded at the speed of light, there would be more stuff in the observable universe. Assuming intelligent life lasts long enough, at some point, the only things left to see would be the celestial objects in our galaxy.

Vor 2 Monate
Lakshay - Musical Scientist
Lakshay - Musical Scientist

@Belladonna High i know the age of the universe I used the term as an assumption to explain better and about the 40 km/s thing it's way more than that, maybe even expanding faster than the speed of Light, and it expands everywhere equally it just appears to be slower to an observer watching a body with high gravity or extreme speed resulting in time dilation

Vor 3 Monate
Belladonna High
Belladonna High

@Lakshay - Musical Scientist I know very well that what we see is not how it is. We even see other people how they were by just a tiny percentage of a second. It is there but it's not noticeable b us. We are constantly looking into the past so to speak. How about music? Sound is so slow that in terms of speed we can say we are looking into the future while seeing an explosion in the distance - we know what to expect. And the Universe is 13,7 billion years old, not 10, as well as expanding with the rate of 40 KM/s (I think), so nowhere near the speed of light and it's not expanding everywhere at the same rate, I wonder if it doesn't at all somewhere...

Vor 3 Monate
Colby Black
Colby Black

So I was told to think of galaxies drawn on a balloon being inflated and moving away from each other to represent the expansion of the universe, but seems too simple and limits the description much like using flat planes with weights in the center to describe gravity. Instead of galaxies being on the surface of a balloon, I imagine each galaxy in the center of its OWN deflated ballon. I picture a galaxy suspended in the center of each deflated ballon. Now gather all the balloons together so they are touching, and suspend them in a vacuum so they float and surround each other and then create a process that inflates them from the inside. White hole in the center of each galaxy similar to air blowing into the balloons. What would happen? What would that look like? Each balloon would expand towards each other but it would separate the galaxies in the center of each balloon more and more. Let’s give the balloon infinite elasticity. The balloon would expand forever away from the galaxy in the center and also push the individual galaxies further from each other at twice the speed. Now I’m curious, and similar to point of the equivalent principle, when you make all of the balloons transparent, and then observe the different reference points ( from out side looking at all of the balloons, or inside a balloon, looking at the center of its galaxy, or in a balloon looking at all the other galaxies, there is no real difference between describing the expansion of that invisible balloon around the center of that galaxy or simply saying the galaxy is forever falling towards the center of the balloon away from all the other transparent balloon galaxies. My next point would be, would be we already know the baloons are expanding because we set up the hypothetical thought experiment that way. Lets take it a step further, keep the balloons transparent and put an observer in one of the balloons. Tell him that each galaxy is falling toward its center into new space time. Put another observer in a different balloon and tell him the opposite, that each galaxy had space expanding outwardly from each galaxy. What would change for each of them? How would they test it? Make sense? And the point to that is, what if we don’t have black holes at the center of the galaxies, we have white holes adding energy for expansion. And just like the Big Bang created time with expansion, what if there is what our experience of time is. So it seems like we are objects falling through the expansion of space constantly, creating acceleration/gravity and the experience of time which is simply units of measurement as space time expands and flows “around” objects at different rates depending on its mass.

Vor Monat
Raging Poo
Raging Poo

I agree that this concept depends on the observer. So, if a lens were moving away from the observable universe at a speed greater than the rate of its expansion, then it would appear to be shrinking instead. Therefore, we cannot conclusively say that the universe is, in fact, expanding.

Vor Monat
Leifur Hákonarson
Leifur Hákonarson

Although Google tells me that the word "lense" doesn't exist in ANY language, I'm going to guess German ....

Vor Monat
Collin Fox
Collin Fox

Could you do a video on how we were able to measure the distance from the earth to the sun? Many videos I've watched related to this give a sun-moon angle of 89.853° as being the basis of their calculations, but don't explain how they got this angle.

Vor 2 Monate
wailinburnin
wailinburnin

I’m pretty sure there’s a principle of symmetry that would mean that you can run the entire “universe expanding” thing through a different set of language. It could be that the universe is not expanding, but that every property of the universe is losing its efficacy, meaning, all the stuff in the universe is getting smaller. This means everything measured as at a constant value is staying the same relative to the measuring instrument which is experiencing this same rate of magnitude loss. This type of model, which is really only a different way of communicating the information, would mean that the “whatever the universe is made from” is the same conceptual “size” for the entire life of the Universe so that the end of time and beginning of time are essentially the same situation rather than the “expanding Universe” model where you start with a conceptual point that expands forever until all the mass is gone (decays) and with it, all the pulsation that marks time.

Vor 7 Monate
Indawg Wetrust
Indawg Wetrust

are you high

Vor 6 Monate
Damon Edwards
Damon Edwards

I have thought the same thing, but you articulated it better than I could.

Vor 7 Monate
Jeremy Gross
Jeremy Gross

I was thinking that since gravity affects acceleration and causes red shift even just here on earth in a tower, why don't we consider that it's NOT moving away/expanding but that gravity from the original light source constantly pulled on or deteriorated the photons velocity (and thus the shift)? My best guess is that because gravity falls off with the square of distance, if memory serves, it's not strong enough to do so. I don't know if that's the right answer though.

Vor 7 Monate
Jatin Sanghvi
Jatin Sanghvi

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.

Vor year
Ed19601
Ed19601

@Alex Mullen so he would have outrun the cops, all while driving backwards? What a boss

Vor 7 Monate
Ed19601
Ed19601

And he must have been driving backwards

Vor 7 Monate
Namish Chhabra
Namish Chhabra

Well, in his reference frame the whole universe was speeding the opposite direction he was going.

Vor 8 Monate
SUPERMAN
SUPERMAN

@Dhichic Pop YES IT SMELLS REALLY BAD. ---------- LIKE DOO DOO 💩

Vor 9 Monate
Dhichic Pop
Dhichic Pop

@Ritik no it just means that time will pass slower for him. Travelling to the future is impossible as there is no such thing as the future. Time here still goes forward for him so he does not time travel to the future or the past

Vor 9 Monate
Stanislav Lebedinskiy
Stanislav Lebedinskiy

Hmmm. Can we use red shift to prove/measure speed of light in different directions? If it is different depending on direction, wouldnt it redshift differently?

Vor Monat
Donald Junior
Donald Junior

I always thought of the expansion of the universe in the way that time and space are not equal that's why the universe is expanding and in quantum mechanics time means little and probability is king . Think of time as a sheet over a two dimensional space as gravity is introduced you get the curvature of space with the curvature of time it looks all most the same but gets pulled a little bit more or maybe it's space that gets pulled More eather way one is not equal to the other at least that's my thought

Vor 6 Monate
Bluustreak
Bluustreak

Uhm, now I'm curious; this is the first time I've heard that redshifting is due to the space-stretching of photons. I've been thinking about this topic a lot and will inevitably like this video o:

Vor 7 Monate
Jeff Paborada
Jeff Paborada

For it to expand, you must need a space. So does that mean outerspace is expanding on "outer space?" Is the outer space finite? Will the expanding end?

Vor 7 Monate
Leopoldo Hortaleza
Leopoldo Hortaleza

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.

Vor year
EclecticByTea
EclecticByTea

@Science Revolution Is that too basic for you? How about ever growing dense rip in space fabric?

Vor year
EclecticByTea
EclecticByTea

@Science Revolution Because if it isn't then I'll explain to you the light around the black hole. If the light can't escape then that means that it pulls everything in right? And it's all moving at great speed which means that it is going to be very bright. Even if you claim that the black hole just sucks everything in (which it does) that's still no excuse to saying that you can't see the light entering the black hole. The picture is of a black hole tearing a star apart. Maybe you should've done some research before you made this arbitrary comment, unless you're joking, then I mean no harm.

Vor year
Brad Steeg
Brad Steeg

Hey, thanks. I assumed everything was expanding except that it took longer to do it in the presence of gravity due to slowed time. And I guess I really don't know what expanding space means; i.e. are units of space increasing in number or are they getting larger. Makes me feel like the space between my ears is expanding.

Vor 7 Monate
RagingGeekazoid
RagingGeekazoid

No one even knows what regular space means. Relativity describes mathematically how much space expands depending on the circumstances (i.e. density of mass, energy, and momentum), but it doesn't really explain what's happening at a microscopic level. That would require the "theory of everything" (relativity + quantum mechanics) that physicists have been trying to figure out for the last century.

Vor 7 Monate
Dustin
Dustin

1.I forgot I've watched this video before and remember not understanding it previously; however something clicked this time. I think the issue, beyond my own lack of brainpower, was your explanation made it sound like the observers were simply watching from outside while observers inside were measuring with equipment. It wouldn't matter that the ship was stationary when emitting the light, as the light is going to move at a constant within a vacuum, assuming that the emitter and measuring device were in a vacuum built on board. To the inside observer there will be a red shift, while to a stationary outside observer, using their own measuring equipment would register no red shift. 2. We are expanding, or contracting, depending on your relative location and measuring equipment used. To that I mean, if someone were to be able to place a scale 'in front' of you, as our galaxy is moving in a general direction at some measurable speed, then you would 'weigh' more than you do on earth, relative to your perceptively stable position. At the same time, if someone were to put a scale behind you

Vor 7 Monate
Bob Brown
Bob Brown

Interesting for sure, some of it over my head, still don't know if this captures what is expanding. Maybe what is not, but what is? If the Universe is expanding at the speed of light, does that mean that we are getting further from the Sun. If so, at what rate?

Vor 6 Monate
l3mmsipvro
l3mmsipvro

Only things which are not bound by gravity and/or the weak or strong forces expand. Nothing within the galaxy cluster will expand; the other forces are too strong for dark energy to overcome.

Vor Monat
Jimmy cozzy Costine
Jimmy cozzy Costine

We are expanding within our galaxy, like you would travel in an airplane👍

Vor Monat
Antonio Prince
Antonio Prince

Outstanding video. Thanks for your great interest is presenting science to laymen like us. 👏🏻👏🏻👏🏻👏🏻👏🏻💎💎💎💎💎

Vor 7 Monate
Snow Santa
Snow Santa

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

Vor year
Yooless
Yooless

Love your videos. Every single one I have seen. And those are an ever increasing number ;) For this one, I have a question: At 282 ( 4:42 ) you say that it makes sense, that the photon was redshifted if the rocket accelerates after emitting a photon along its length. But... Everyone observes the speed of light as the same speed, so the people in the rocket experience slower time, right? Why does that make it redshifted?^^ Is it, that the photon still moves at the same speed, but somehow... elongates? Am I simply neglecting the "space" aspect of relativity? Corrections and explanations would be highly appreciated! Have a great day :)

Vor 8 Monate
Koray yy
Koray yy

@Yooless We need to know if the light source is coming towards you or going away from you first. If it is going away from you you will see a redshift.

Vor 7 Monate
Yooless
Yooless

@Koray yy Oh, I see! Thank you for clearing that up :) So I even had the right idea about relativity, just insufficiently precise to include light... right? The frequency is how we get to lights spacial aspect, the wave length, so in a less accurate way it does actually elongate?

Vor 7 Monate
Koray yy
Koray yy

Photons go with the speed of light c and let's say they have frequency f. We'll have λ = c/f where λ is the wave length. The color you see is related with this wavelength. Red shift means the light wave length will be longer and from the equation you can see that the frequency should be less. So red shift is about how we observe the frequency and the wavelength differently in different reference frames.

Vor 7 Monate
YK
YK

What baffles me all the time is how the existence of cosmic background radiation is reconciled with the very first principle of relativity? The fact that we can have an observer at rest with respect to background radiation sort of indicates the existence of a preferred frame of reference.

Vor 4 Monate
Euro Wars
Euro Wars

I thought red shifting was a function of time? Also, do the actual photons expand or does the distance between them get bigger as they travel?

Vor Monat
packtech
packtech

I have been thinking about this for a while now. My 'Thought experiments' tell me that actually light travels at an infinite speed, but as the universe it expanding (Space-Time is expanding) light in our universe seems to have a speed limit, we can't experience this Space/Time expansion as we are all part of it.. For instance, if light travels at an infinite speed from point A to point B, by the time it 'gets to point B', point B isn't there anymore.Expanding Space/Time has been stretched it away , so it appears that light is somehow limited.

Vor 7 Monate
Stephen Rhodes
Stephen Rhodes

i was thinking something really similar to this. except I think the universe is expanding at an infinite speed, instead. because if light were traveling infinitely fast, than it would be faster than the 'universe.' and if you shot a beam of light out in space than eventually it would pass space itself. space cant be infinite and not expanding. so the universe is instead traveling and at infinite speed. thats my tought

Vor 7 Monate
DeadTurret
DeadTurret

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

Vor year
Jay Fredrickson
Jay Fredrickson

Stars, briefly.

Vor year
Vigilant Cosmic Penguin
Vigilant Cosmic Penguin

He sees some dude with a beard explaining astrophysics and pointing at him

Vor year
Mountain Drew
Mountain Drew

He appears to be going down at just about the same speed as the photons, soooooo he would probably see himself cause a nuclear explosion with the air.

Vor year
bmoneybby
bmoneybby

That pavement looks Hella blue..

Vor year
Meitti
Meitti

A pair of broken legs, if he's lucky.

Vor year
TCL
TCL

It’s probably just me, but I’m always wondering what the expanding universe is expanding into.

Vor 7 Monate
HascleAvrahm BenYoseph
HascleAvrahm BenYoseph

That's a very good point! I would think it must be bumping into itself. Another weakness of the expansion theory is that it implies that the earth is at the very center of the entire universe. Gee, what a happy coincidence! 🤣👍👍 My Theory: Surely the laws of nature must apply to everything. That must mean that we are proof of the truth. Yes, aliens do exist and no, the universe is not expanding.

Vor 4 Monate
hosh1313
hosh1313

Gravitational blue-shift implies that photons have mass and gravity does work on them, assuming c is constant. I would suggest c is not constant and that if a photon is blue-shifted due to gravity then it's speed decreases in a way that satisfies the Law of the Conservation of energy. It is either this, or a photon has mass - take your pick!

Vor 5 Monate
Honey Singh
Honey Singh

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.

Vor Monat
Len
Len

Just for the record - the observation would be exactly the same if we were actually shrinking! (Due to a cooling universe for instance )

Vor 29 Tage
GDI Bass
GDI Bass

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

Vor year
Shaurie Pvs
Shaurie Pvs

@Mark B because of space time curvature you gained velocity and accelerate down but enough force if applied can stop any acceleration... So the normal force is the electromagnetic force by the earth being applied on you to stop you getting accelerated down (due to spacetime)

Vor year
DeusExAstra
DeusExAstra

@Mark B Yeah, the normal force you experience with the surface is a result of spacetime dragging you down towards the surface. So in a sense you're accelerating down towards it, but it's not because of a "gravitational" force, it's just that you're gaining speed from your speed through time being curved into the space dimension. Confusing, I know.

Vor year
Mark B
Mark B

@DeusExAstra isn’t there a normal force accelerating you up with the same force as gravity? Or did I miss read something. Because that would mean: Fnormal = Fgravity Or do these not apply in relative physics?

Vor year
Shawn H Corey
Shawn H Corey

Here's another way to think of it but some may strongly disagree. In general relativity, inertial frames are local, that is, they do not extend very far. But what if the frame was effected by gravity? It would fall and drag you with it. You would feel no acceleration because the frame is falling with you. But when standing on Earth, the frame keeps falling even when you don't. Your inertial frame is being accelerated away from you and you perceive this as a force pulling you down. Falling frames is one way to look at gravity that might be easier to envision.

Vor year
Sonal bhattacharya
Sonal bhattacharya

But the reality is gravity is not real. No where!!!

Vor year
Gabe Gibler
Gabe Gibler

I love the phrase "properties of the photon-observer system".

Vor 5 Monate
Turam Purty
Turam Purty

Our universe is expanding more than it's contracting when we look out into space, but it's reversed when we look into matter.

Vor Monat
The MinecraftR 9598
The MinecraftR 9598

Well, surely the space between the particles that compose me is indeed expanding, it just so happens that the forces holding me together pull the particles back in towards their stable states constantly, right? If I am, then it isn’t quite true to say definitively that space isn’t pulling me apart, but rather that the forces holding me together are able to pull me back together constantly

Vor 7 Monate
William Smith
William Smith

Our understanding expands, and thus the universe must expand so that we humans do not outpace existence itself! Like playing a game and getting out of the map 😃

Vor 7 Monate
cyto
cyto

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

Vor year
HascleAvrahm BenYoseph
HascleAvrahm BenYoseph

Old New York expression: If you don't like the weather, wait a minute. 👍

Vor 4 Monate
Protheus
Protheus

There will be no "after corona", it won't be over any time soon. That's it, it's with us for the foreseeable future like flu.

Vor year
Alex
Alex

Ok, Thanos

Vor year
Scott Bentley
Scott Bentley

How do we know (what evidence is there) that the Universe is expanding (a square today is smaller than a square tomorrow) and energy is being stretched to fill this new space, rather than that the geometry remains static (a square today is the same as a square tomorrow) but energy is shrinking (more energy fits within the same square)? Conceptually speaking, the result would appear the same to us as we, being made of energy, would see all of existence around us "moving away" and the size of the Universe would appear to "expand" around us, right?

Vor 7 Monate
Thomas Noonan
Thomas Noonan

Question: @4:50 he explains that the observers in the ship see the photon as red shifted due to them moving away from the source when the light was emitted. But why would they be analogous to the observer at Harvard if the observer at the top of the Harvard experiment is stationary relative to the source when the light was emitted?

Vor Monat
William
William

Action lab had an amazing explanation comparing it to the doppler effect as seen in trains.

Vor 8 Monate
Getis Realis
Getis Realis

The outer rim of the universe is in itself, gravitational.Think of it as inverted gravity, presented as a front. So the analogy is, the expanding front is low pressure. The inner universe, high pressure, is trying to fill it.

Vor Monat
Jonas Larsson
Jonas Larsson

Assuming there is an outer rim

Vor 9 Tage
raoul herbord
raoul herbord

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

Vor year
Amaraticando
Amaraticando

There's nothing expanding besides the "metric".

Vor year
Elleaf1
Elleaf1

I did too and then I thought I found the answer in a Philip K. Dick story where a man time travels (sort of) and the people from like15,000 years ago are tiny since he would be more expanded. They think he is god and it turns out he gives them the 10 commandment or something. But now I'm mad because I told other people we expand since I thought it was true because of that story I feel so lied to or something

Vor year
OZZYmandias_twenty14
OZZYmandias_twenty14

What is happening is more space is being created. Now could this new space creation get to a point where it could eventually overcome all the forces holding things together? Maybe. The Big Rip theory suggests that the expansion could continue that far. But its too soon to say if that will happen. Dark energy grows over time? I think so but is it infinite or finite? If finite will the acceleration lessen and stop? Before the universe smears out into homegeniaty? I doubt I'll be around that long to find out. 😎😆

Vor year
Adi Bawne
Adi Bawne

Really, my friend. I have been thinking about that same question for a while now.

Vor year
blueckaym
blueckaym

We know that light sources moving to/away from us can cause doppler shift in the wavelength of the light they produce, but does a moving observer also perceive a doppler shift because of his own movement? I mean if a star's light is shifted to a wavelength λ because of the star speed, if it doesn't get shifted further during travel (ie ignoring cosmic expansion red-shift for now) then we would assume it would arrive at the observer with wavelength λ. But if the observer is also moving with considerable speed relative to that light source, then would he detect additional red/blue shift on the moving detector? I was thinking about the setup of the experiment at 7:56, for a single photon the only way to observe it and pass it further is to absorb it, measuring its properties and generate new photon with the same properties. Is such case every observer on the chain would be new light-source, which we know can shift additionally the wavelength because of its relative speed. But if you consider a beam of light, and after all stars are radiating light in all directions, ie given beam of light would spread wider as it travels further, which means that a detector can be setup to intercept only a small fraction of it, while the rest of the beam is left untouched by measurement, and doesn't need to be re-emitted. So at every observer in the chain we can take a small sample of light to measure the light properties (assuming they're mostly homogeneous with the rest of the light in that beam), and let the rest of the beam travel with its wavelength untouched since its original light-source. I assume when the last observer takes a sample and compares with the light that was re-emitted by every other observer on the chain, its wavelength should be the same. And I assume the only factors for a doppler shift of a wavelength are both speeds of the light-source and of the observer. Expansion of the spacetime just affects these speeds. So the actual red-blue shift only happen on emission and on detection of photons, right? I mean that if I'm observer on a planet moving away from the star I'm observing because of the Cosmic expansion I'll detect a red-shift. But if I'm moving at a speed that allows me to keep the same distance with the observed star (ie relative speed to the star is 0) I wouldn't detect a red-shift at all (no matter if you consider the light red-shifted at the star, and then blue-shifted the exact same amount on detection because of my speed) Is that right?

Vor Monat
Nicholas Leclerc
Nicholas Leclerc

So let me get this straight; when you are in a non-inertial frame of reference, with a coordinate system that immobilizes every entity of interest containing in place relative to one another, you get a redshift that can be *technically* called a Doppler one because, from any of the observers’ perspective, the light(‘s) source is technically immobile and thus in an inertial frame of reference relative to you, yet still has a recorded redshift; which constitutes the definition of the Doppler shift : A constant velocity vector emitting light with a redshift This is equivalent to an intergalactic coordinate system that keeps its neighbouring galaxies “co-observer” yet still detects an (increasing) Doppler shift (due to the fact that Cosmic Inflation increases with distance, and so thus the equivalent instantaneous velocity of the neighbouring galaxies you’d have to give them at any given time for the instantaneous Doppler shift that you measure from them, but…); …the point is, that you don’t have to incorporate movement or distanciation in your physics, in order to have a redshift; because the Doppler effect could just arise anyway if that’s how the universe ever worked Hence your premise in this video, which is that *even though galaxies accelerate away from one another* , it doesn’t have to be because of that that we see a redshift ? And then, we can’t see a Doppler shift at our scale, because the assumptions we make to simplify the physics without leading to non-negligible changes are completely different : There’s grvaity in one preferred direction over others, and we can CLEARLY see an asymmetry in mass distribution, as well as having relatively very much stronger electromagnetic bonds keeping us tied together (the equivalent of a human-shaped human with a size comparable to the observable/entire universe with super strong gravity binding every single element together)

Vor 8 Monate
Martin Vandenbroek
Martin Vandenbroek

It's worth reading the book by Dr. Mark McCutcheon, "The Final Theory", which goes further into this issue of expansion theory to explain many of our questions.

Vor 8 Monate
Biswarup Ray
Biswarup Ray

What if the final constants are changing over time which causes the universe to expand?

Vor 2 Monate
Cricket Fans 777
Cricket Fans 777

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!!

Vor year
Fish
Fish

6:01 "Well for this we have to zoom waaayyyyy out". To what place can you zoom (way out), such that galaxies in the observable universe look like molecules in a fluid, and look "the same in every direction"?

Vor 7 Monate
The deck to the 16th power
The deck to the 16th power

Weird but it seems expansion accelerates time yet compresses the past time into greater quantity. A part of energy conserved is time or a time being conserved.

Vor 6 Monate
Eric Verbeek
Eric Verbeek

Thank you! I have so many beefs with cosmology, and I still have skepticism of the expanding universe, but this is the first time anyone has cut through and stated that it isn't the *space* that the theory says expanding and pulling things apart. Thank you so much for this. That never made sense to say. Is the expansion akin to diffusion?

Vor 4 Monate
Deacon StJohn
Deacon StJohn

space is expanding, it just doesn't pull things apart because they are held together by other forces

Vor 3 Monate
Gangadhar Hiremath
Gangadhar Hiremath

Difficult for me to comprehend but this field of knowledge attracted me since my teenage.Not understood much all these 50 years but I continue to pursue. What is "cosmic fluid"? Is the universe immersed in this soup?

Vor 7 Monate
Sambhav Bhalla
Sambhav Bhalla

Consistent uploads with quality wow how's that even possible

Vor year
AJ
AJ

@Ethan M I mean he probably recorded a lot of videos and is now releasing them in a regular schedule, instead of releasing them immediately when they are finished

Vor year
Crank
Crank

A lot of hard work by great team. Keep it up guys! :)

Vor year
Franklin Allen
Franklin Allen

Sweet, sweet sponsorship income = more financial resources = more better content.

Vor year
Ethan M
Ethan M

@AJ prerecorded?😂 To what? Xd

Vor year
Dylan Zondag
Dylan Zondag

Scientists keep thinking and there are still things to discover

Vor year
UnimatrixOne
UnimatrixOne

Is the room/space being stretched or are new "parts" of the room being added over and over again? The question is, will the space itself expand or will new parts of space be added?

Vor 7 Monate
UnimatrixOne
UnimatrixOne

@SKEKSIS That wasn't my question at all! The question is, will the space itself expand or will new parts of space be added?

Vor 7 Monate
SKEKSIS
SKEKSIS

Neither, gravity and the strong force are strong enough to counteract the expansion of spacetime on a local level. The space you are in still expands, but those two prevent you from expanding along with it

Vor 7 Monate
Kevin Watts
Kevin Watts

The void, or darkness of space is endless for infinity. The expansion is the existing matter like Stars, planets, dust, gasses and light which is constantly expanding.

Vor 5 Monate
Jim Jimmy
Jim Jimmy

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?

Vor 4 Monate
Mohammad Ahmady
Mohammad Ahmady

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

Vor 4 Monate
Noah Day
Noah Day

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

Vor year
Best Gun
Best Gun

@Noah Day oh, ok.

Vor year
Noah Day
Noah Day

@Best Gun Oh, I hadn't seen that yet

Vor year
Best Gun
Best Gun

He made a community post where he said he has a team now.

Vor year
maratreus ,
maratreus ,

This is the phrase I heard today

Vor year
Doug Nichols
Doug Nichols

That sponsor money getting put to use

Vor year
Tofran Bohk
Tofran Bohk

If there are two galaxies that are moving in the same direction at the same speed, therefore they are stationary relative to one another, are they actually getting farther apart because the universe is expanding?

Vor Monat
Jeff B
Jeff B

If the electromagnetic force stopped holding the molecules of your body together, wouldn't they still be gravitationally bound to eachother and therefore not expand with the universe?

Vor 7 Monate
Matt H
Matt H

I was always told everything is expanding including the atoms in our body.

Vor 2 Monate
Blackmark52
Blackmark52

*"The photons themselves stretch."* Never heard that one before. The explanation I heard was of the doppler effect. Nothing gets stretched. Only the frequency changes depending on the observed direction of movement of the photons. And photons aren't a wave that can stretch any more than they are a tiny unit of matter. They are just reference points on a wave that define its frequency. And that seems to be the conclusion of the video as well.

Vor 7 Monate
Noah F.
Noah F.

@Blackmark52 The things that go on at cosmological scales are so far out of our daily experience that the human brain does not posses the mental faculties to fully comprehend them. That's what makes cosmology so interesting. : )

Vor Monat
Blackmark52
Blackmark52

@Noah F. "a little trickier than the usual doppler shift" thanks for the explanation, it helps, but it's still hard for me to wrap my brain around.

Vor Monat
Noah F.
Noah F.

It's a little trickier than the usual doppler shift since the redshift continues while the photon is traveling, not just due to the relative velocities of the emitter and observer. In the video, he says you can view the continuous redshift due to the expansion of the universe as a series of tiny doppler shifts at each point in space. It's like the sound a car would make when it drives past you, but if the road between you and the car is also expanding at an accelerated rate.

Vor Monat
Blackmark52
Blackmark52

@Eric Ray "he meant Doppler shift." Derek initially talks of the Doppler Effect as one explanation of redshift. The photons stretching is another option. That's kinda the point of the video asking if everything is getting stretched.

Vor 7 Monate
Eric Ray
Eric Ray

I think he just stated it kinda weirdly. I’m pretty sure he meant Doppler shift.

Vor 7 Monate
Мариос Христодулу
Мариос Христодулу

I'm surprised to hear that the common explanation for the cosmological redshift is that light itself gets stretched out. I have actually never heard that explanation before. The only one I've ever heard is the one that involves the Doppler shift due to far away galaxies moving away from us due to the expansion of space.

Vor year
isonlynameleft
isonlynameleft

I've heard both explanations, it's just easier to explain it that way to someone if they don't know anything about relativity.

Vor 3 Monate
Markus Karzelek
Markus Karzelek

Yeah, maybe it’s an US thing. In our school in Germany we were taught, it’s because of the Doppler Effect.

Vor 4 Monate
tim harrell
tim harrell

In cosmological red shift, where does the energy of the photon go ? (As in energy is proportional to frequency or 1/wavelength.) In normal doppler, one accepts that the relative motions explain the energy loss. But in cosmological red shift, does the energy go into the expanding space ? Is it enough to explain the expansion ?

Vor 6 Monate
Melinda Green
Melinda Green

Hang on. Lewis' paper says "that there is no physical experiment our observer, could do to distinguish between being at rest in a gravitational field or being inside a uniformly accelerating rocket in deep space." But if the ship is standing on the ground, an observer at the top should be able to measure a lighter gravitational force than one at the bottom, simply because they are slightly further from Earth.

Vor 6 Monate
Ingmar Kronfeldt
Ingmar Kronfeldt

Question (a brilliantly stupid one I hope): Time stands still for photons (relativity/Einstein), so when does it have time to oscillate, travel around objects along the shortest path, be stretched out, talk to its entangled buddy and so on? It is created and then "dies" at the same moment, in the same spot, right, but then finds itself potentially billions of light years from home (except it never gets to experience it, since it "dies"). How does this work? Does electromagnetic give us answers here, or where should we turn?

Vor 7 Monate
Gregory Stocker
Gregory Stocker

I’m no expert, but listening to Roger Penrose he had an interesting thought about this. He said once the heat death of the universe occurs it will become only photons because all mass will have been turned into energy through Hawking radiation seeping out of the last black holes. He said that once photons are the only thing that’s left in the universe, since time is relative and so is distance, the space between the massless photons will lose all meaning even though they have been stretched extremely far apart. He postulated that this state of pure energy that has no meaningful sense of time or space becomes indistinguishable from the conditions of the Big Bang. So I think asking what it’s like for a photon is that time doesn’t exist and has no meaning from a photons point of view. Infinity is a single moment which is pretty impossible to imagine.

Vor 7 Monate
squeakeththewheel
squeakeththewheel

New results (2021) from gravitational wave observations imply the size (and mass) of black holes are expanding/increasing. I guess that is because a black hole is really an aspect of space-time, not an object held together by any forces.

Vor 7 Monate
decay
decay

I love the direction this channel is moving in. I've not seen any channel as big as Veritasium trying to explain these interesting theories about relativity and space, especially in such an understandable manner. Nice work man

Vor year
herlsone
herlsone

Arvin Ash does a great "laymans" job at this also.

Vor year
Gurender Singh
Gurender Singh

"It matters a lot on who is doing observation". Welcome to universe which is Maya. Temporary, ever-changing, incomprehensible, indescribable.

Vor 4 Monate
Undying EDM
Undying EDM

So, Blue-shifting would occur if the external observer was travelling *towards* the source, at a faster rate than the expansion of the universe?

Vor 8 Monate
Ramin Safakish
Ramin Safakish

It’s amazing how this video shows “my significant less gray matter” than physicists.

Vor 4 Monate
Lawrence Burleson
Lawrence Burleson

What if you had a glass box and threw it out into space. The inside of the box is a vacuum and the outside is also a vacuum. Would the box stay the same size or would the space within the box slowly expand until it exploded.

Vor 8 Monate

Nächster

Why Gravity is NOT a Force

17:34

Why Gravity is NOT a Force

Veritasium

Aufrufe 8 800 000

This Particle Breaks Time Symmetry

9:00

This Particle Breaks Time Symmetry

Veritasium

Aufrufe 4 100 000

Is Most Published Research Wrong?

12:22

Is Most Published Research Wrong?

Veritasium

Aufrufe 4 400 000

I Delivered a Penny to MrBeast!

17:36

I Delivered a Penny to MrBeast!

Ryan Trahan

Aufrufe 6 875 904

Chaos: The Science of the Butterfly Effect

12:51

Is Dust Mostly Dead Skin?

15:13

Is Dust Mostly Dead Skin?

Veritasium

Aufrufe 3 900 000

Spinning Black Holes

10:14

Spinning Black Holes

Veritasium

Aufrufe 4 700 000

Turbulent Flow is MORE Awesome Than Laminar Flow

18:32

The Discovery That Transformed Pi

18:40

The Discovery That Transformed Pi

Veritasium

Aufrufe 9 900 000

This is why we can't have nice things

17:30

This is why we can't have nice things

Veritasium

Aufrufe 17 000 000

Math's Fundamental Flaw

34:00

Math's Fundamental Flaw

Veritasium

Aufrufe 20 000 000

I Delivered a Penny to MrBeast!

17:36

I Delivered a Penny to MrBeast!

Ryan Trahan

Aufrufe 6 875 904