So is sunlight old? Or not old? Watch the whole video and let me know what you think! And you can always come find me on Twitter/Instagram: @DrJoeHanson @okaytobesmart
@Rajeev Vij no. There is no perspective that moves with c with respect to something with mass. You can't just use the time dialtion formula without thinking.
The fact that the density decreases the further out from the core you go, actually adds a bias towards leaving the centre. You're more likely to collide with something on the way back in, so it's easier to go out, even if it's just a minuscule difference.
And now imagine that this does not only happen in the sun, but also every other star. Most of them are millions or billions of light years away and way bigger than our sun. This means every single photons fights it's way through immense temparatures and unimaginable high pressure for thousands or millions of years only to then travel through space time for another few million or billions of years, only to then reach your retina so you can look at the beautiful night sky. And every time you don't look at the stars, or you do look at them but simply start to blink, all this effort, all the amount of things this Photon went through, is "wasted" for you, because you didnt see it. It's so tragic that it's almost poetic and beautiful.
I bieve he is referring to the approx 100k years it takes for photons once emitted from the core to get to surface. Then it's ~8.min to earth. Gravity!
@@drzecelectric4302 photons don't travel through atoms. They get absorbed by atoms which could then emit a new photon. All of the photons we see from the Sun are 8mins old.
2:03 That phenomenon of the sun staying stable because its pressure is pushing outward and its gravity is pulling inward is called "hydrostatic equilibrium." That's also how planets like Earth maintain an atmosphere that extends upwards instead of floating away or getting squished against the surface. I don't know why that one phrase in astronomy 101 stuck with me so well.
Is it really the "same photon" after each interaction with a proton/particle within the Sun? Is that singular photon 170,000 years old, or does it just take 170,000 years from the original reaction of creating a photon, to an equivalent photon being released from the surface of the Sun?
Normally with an actual atom of something, a photon would be absorbed by an electron, which then generates another photon. However in the case of the sun, the immense heat and pressure causes the electrons to separate from their adjoining protons(which is the definition of plasma as a state of matter), which means the photon is actually colliding with a proton. Proton's cannot be excited like electrons and thus the energy is not absorbed, but rather bounces off. This means it is in fact the same photon. Electrons do still exist within this soup of protons though and some photons may become absorbed if they do manage to actually hit an electron.
@@setcheck67 Plasmas simply are states of matter in which SOME or all of the electrons have been stripped away, the key being that positively charged nuclei (Ions) can roam freely. It's a charged gas with high electrostatic interactions. Add to that the "Atmosphere" around the sun which creates absorption lines in the spectrum indicating the specific energy levels absorbed by the atoms and then re-emitted as photons and I'd lean more towards @Rachel Losacco being correct. I get that it's semantics, but she has a point.
@@andredbraxton She asked a question. A question of semantics, but a question nonetheless. So why are you phrasing this as though I'm calling her wrong when she did not provide a statement? Breaking it down to the deepest level, a photon is nothing more than a carrier of electromagnetism AKA energy. ALL OTHER THINGS CONSIDERED, energy cannot be created or destroyed, but mass can be converted into energy and energy into mass. So to break it down to the most semantic way possible... That photon was created when mass was converted fusing 2 hydrogen atoms to produce helium. That photon continues to exist AS THE SAME ENERGY until it meets another photon and forms an electron - positron pair. Only at that time has it stopped being the same energy. Thus it was born at that instant and "died" when it became mass.
@@setcheck67 No need to take it as a personal attack. I was simply pointing out that through 2 leaps in assumptions (1-in the sun electrons separate from protons, 2-photons can only collide with the protons) you claimed that 'plasma has no associated atom-electron structure and leaves photons with only protons to collide with in the sun' as the basis of your counterpoint. It is a flawed assumption, and the reason I gave you two examples of why that assumption doesn't apply to the case of our sun (1-plasma often has electron-proton structure, 2-There is a photon absorbing atmosphere for photons to traverse as demonstrated by absorption lines in the sun's spectrum) To your second response about mass-energy conversion. A photon striking an electron in an atom is NOT the same photon that is emitted from the collision. This can be easiest represented by the difference in energy levels in Neon. When struck with a photon of green light, only some of that energy is first released as an orange light photon, then again as another photon as it drops to a lower shell... and then another lower energy photon as it settles into its original lowest level energy shell. SURELY you would agree that such a reaction has nothing to do with two photons colliding and is another way for energy to be transferred from one photon into another different (or in my example, several separate) Photon. Therefor not the same photon from the fusion event, traversing through the soup of plasma, through the collisions with the actual atoms that absorb and re-emit photons of various frequencies when it leaves the surface region of the sun. These photons are "born" in the fusion event, and "die" when absorbed by an electron that gets pushed to a higher shell.
I know this is semantics, but if a photon strikes a proton and is absorbed (that's why it is losing energy, right?) and then a photon pops out, are we sure it's the same old photon or did that photon "die" and a new one was "born". It's like the Transporter Problem but for light particles.
It's not just semantics, as more photons are eventually produced than absorbed -- hundreds of thousands to millions times more. The nuclear reactions in Sun produce high-energy photons (MeV to tens of MeV -- Mega electron volts), but the visible photons which escape the Sun have energy of few eV (*). The Sun is in radiative equilibrium (its temperature remains stable), so it eventually radiates all the energy produced by the nuclear fusion -- thus it must radiate many times more low-energy photons for each high-energy one. ____ * eV is a nice little unit -- it's the energy does one electron get from being accelerated with one Volt. For example, photons of visible light have energies from about 1.8eV for red to 3.1eV for violet light. For the same reason, the red LEDs require voltages in 1.8-2V range, and violet laser used in Blu-Ray requires about 3.1V -- they all convert electron energy directly to photons.
lol Julian Heeck, a PhD student at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, calculated the minimum lifetime of a photon to be 10^18 years, or a _quintillion_ years. This _alone_ gives photons complete immunity to age shaming. Source: Claire Ely. (July 29, 2013) Big Bang Light Reveals Minimum Lifetime of Photons _Scientific American, website_
1:25 is wrong because when you define sunlight as light that originates from the sun you also have to count the light that is created when electrons lose energy and a photon is released, this also happens at the surface so there is sunlight that from our perspective is actually as old as the time it takes to get here.
@@DingbatToast Pretty certain it won't be, because of how photons literally don't experience time. If it turns out the universe is deterministic and we got insanely good at mapping/simulating all the particles in our solar system, we might be able to simulate where a given detected photon came from and how long ago, and so figure out how long it took to reach our detector since the moment of its creation. But I doubt that would be possible either for a lot of reasons.
I just need you to know that the hand that came out to high five for your sun pun really resonated with me. I will keep that in my heart and soul forever and think of it when I am sad. Thank you.
Great video! Another fun fact about the "turning off the sun" thought experiment: If we'd remove the sun, the earth would continue to orbit it for the next about 8 minutes, the same way we'd still see the sun for that period, until the sun's gravitation field would no longer attract it, since gravity also propagates at the speed of light! :)
I like to imagine how that’d look on a spacetime diagram where 3D space is a 2D sheet. A sort of anti-ripple taking 8 minutes to spread out from where the central depression used to be
Ever wonder how Dungeon Masters are made? It's from mothers lulling their kids to sleep with whispers of *It's okay to be smart. It's okay to be smart.*
FYI to confused people: the orbit animation at 0:55 is really badly incorrect, makes it look like Aphelion and Perihelion are the same distance. Sun should be at one of the foci of the ellipse! Awesome video though!!
#0:31 actually it would take 16 mins 32 seconds... :) this is because the signal to switch of the light still needs to travel to the sun at the speed of light :)
I've had questions about the 'life cycle' of photons since I was a kid and have had no luck getting answers. That is, until this video. Thanks so much Joe.
Considering all the photons that are "trapped" at any given moment you will understand why the supernovas are so bright - all those photons get released in a couple of seconds.
Omg this video is so good. I love the animations, the analogies, so so so good. Seriously impressed with the upside-down number writing. You are a master.
When I first learned this about light, I asked a scientist friend of mine following question: "Is this the reason a supernova is so insanely bright? Is a dying star outshining an entire galaxy simply because 170,000 years of light is all escaping at once?" I still think I'm on to something here, but he explained that this was actually not correct. I'm sorry I can't explain why it isn't correct because I stopped listening when he told me I was wrong, but I'm sure he's right. But still...
Hi Joe! Fellow Austinite here, and I love your show. At 10:00 of this episode you state that sunlight is responsible for all life here on Earth. Isn't that incorrect, when extremophiles have been found in complete absence of light under the Antarctica ice cap, in the sea floor of the Marianas trench, and even several thousand feet below the Earth's crust?
Great question. The jury is out on where/how life originated. If it originated around deep sea vents then you're correct in that not all of life depends on the sun, but evolution allows plenty of time for life to migrate to extreme environments, adapting to them, so it could be that life originated in tidal regions using photosynthesis and then migrated from there, slowly adapting to other means of energy production like radiosynthesis or chemosynthesis (in which case it still depends on ancestors that relied on the sun). If we find life on Europa or Enceladus, that might strengthen the idea that life indeed first arose on Earth around deep sea vents. Phylogenetics is the study of how life branches out as adaptations occur, and it allows us to compare DNA/RNA to try to understand the common point of origin (as all species share at least some common DNA/RNA). Scientists are still looking, but this is the field that's most likely to identify the earliest lifeforms. As an example, Methanopyrus kandleri-a form of deep sea bacteria capable of chemosynthesis-diverged from the common ancestor of the everyday bacteria Staphylococcus Aureus 4 billion years ago! Given life on Earth is anywhere from 3.8 to 4.2 billion years old, that's astonishingly close to the origin of life, but there's no way to know the exact characteristics of this ancient ancestor, only that these two genetic lines diverged way back then. If you want to try this out yourself, go to www.timetree.org/ You can even try something a bit more fun, like the divergence between humans and octopus.
If you’re going to say photons aren’t slowed by the medium in which they travel, then you really need to define “slowed.” To me, it seems that to be considered slowed you’d need to reach your destination later-and have less energy when you reach said destination-than if your path was clear of obstacles. Let’s use a human example. You’re standing at one end of a rectangular building lengthwise, and in front of you is a large maze. Your task is to get from your end of the building to the other at a constant pace. However, you’re given an option: you can choose to make all the boxes disappear. If you stick with the maze option, you will travel at the same “speed,” but the time it takes to get from one end of the building to the other is something like an hour, and you feel physically drained by the end. But if you go with the no-maze option, you’ll arrive at your destination FASTER and with MORE energy. Even though you’re walking at the exact same speed, one option is faster while the other is slower. So by definition, a photon is slowed by the medium it’s traveling in.
I enjoyed this video (and your others), however, at 1:43, it's a bit simplistic to say " light travels in straight lines from the Sun to us and that is why we cast a shadow on a sunny day". Yes, light for the Sun travels in straight lines, but its angular diameter in the sky is wide enough that light rays can cross when objects cast a shadow on the ground, so it is an "extended source" of light. That is why shadows we cast on the ground actually have an umbra and a penumbra, just like eclipse terminology. The umbra is created from the light rays coming straight down and casting the shadow and the penumbra is caused by light rays that cross. That is why in a solar eclipse, as the crescent phase gets thinner and thinner, the light rays become linear when in line with the crescent. So shadows cast at an eclipse change! Shadows have sharp edges with in-line with the crescent and have fuzzy edges if cast perpendicular to the crescent. Eclipse education is my specialty. I have a video called "What Are Fuzzy Shadows? - How To See Them" on my channel called Solar Eclipse Timer. Check it out. Please get ready for the 2024 solar eclipse crossing the United States again. Thanks. Gordon
Photons travel at the speed of light, so they are essentially ageless. It could be a million years since the photon was emitted, but to the photon it was just emitted. Remember, if you are traveling in the 3 spatial directions at maximum speed (c) then you have no velocity left for the time vector. To the photon time has stopped.
You know that special pleasure you get when a couple of things turn out to be connected? Well thanks for both that and the references. Looking forward to drilling in a bit more.
@@American-Plague There's a lot of semantics going on here, but the photons that arrive here are not "the same" ones the core creates. Check out the responses to the pinned comment if you want more discussion but this "old photon" is more of an analogy than physics. Like how people say that Hawking radiation is created by virtual particle pairs right on the event horizon.
@@sogerc1 And photons are basically just oscillations of electromagnetic fields so in some sense photons aren't even a thing plus there is actually a point of transition thanks to the equation of state and conservation laws where where recombination occurs such that atoms start regaining their electrons with both helium and hydrogen having reacquired their electrons and thus become opaque to light with hydrogen in the outermost layers of the sun having acquired an additional electron to fill its lowest s orbital valence shell as H- Helium is primarily neutral with only heavier elements having higher level electrons stripped from them. There are lots of things going on inside stars and ultimately a more realistic system will need to be solved via iterative processes since it is a system of partial differential equations.
@@American-Plague Well the photons that get created in the core due to the nuclear fusion reactions make their way out of the sun as described in the video and with every collision give off a bit of their energy to atoms in the sun. This energy is in the form of heat, thermal energy in the vibrations of the atoms and the thermal radiation that they in turn give off is what we see on earth. So yes all the suns energy comes from the core in for of high energy photons but the majority of photos that reach us are from the surface
The old college dorm was named Moore. It wasn’t always so easy to walk into, so when we broke the glass door we wrote that meme on the plywood they used to cover the hole.
I like how 'The Expanse' series renames the Sun to Sol and the Moon to Luna. Most likely this will be necessary when humans begin to populate the solar system.
I could be making a mistake but I think the statement that photons are bouncing around and loosing energy might be wrong. The photons must be absorbed by a particle which then release one (or more) photons of lower energy. And the difference in energy is turned into heat (particle's momentum), which in turn can turn back into light (black body radiation). Either that or I have to review my understanding of particle physics.
Smaller stars are emitting more low energetic light (infrared light) and bigger ones more high energetic light (like UV light). How can you describe this with the random walker? I mean the way out should be far longer in a bigger star and this should lead to more low energetic light (like the IR light).
Really GREAT video! I was intrigued by the numbers, and have tried to "do the sums" regarding the predicted length of time for a photon to exit the Sun's interior in a very simple model (that is, the hugely long time you get!). This is what I did -- I hope it makes sense! Many thanks for your wonderful resources! Stay safe! ;-) // Radius of Sun (m) Rs = 690 x 10^{6} // Volume of Sun (as a sphere) (m^3) Vs =4 pi Rs^3 / 3 Vs= 1.37605528 × 10^27 // Number of protons in Sun Np = 10^57 // Volume occupied by a proton (m^3) vp = Vs / Np vp = 1.37605528 × 10−30 // Closest distance between protons on cubic lattice (m) dp = vp^(1/3) dp = 1.11227445 × 10^−10 // Total distance of random walk from centre of Sun to outside = Rs // Step-length in random walk = distance between protons = dp // Random walk formula: "total-distance = step-length x ( number of steps )^(1/2)" // Number of steps in random walk
n_rw = (Rs / dp)^2 n_rw = 3.84834732 × 10^37 // Total distance of random walk (m) D_rw = n_rw x dp D_rw = 4.28041839 × 10^27 // Speed of light (ms^-2) c = 3 x 10^8 // Time for random walk (s) t_rw = D_rw / c t_rw = 1.42680613 × 10^19 // Time for random walk (y) T_rw = t_rw / (60 x 60 x 24 x 365.25) T_rw = 4.52127579 × 10^11 T_rw = 452 Gy
I would be interested to know the mechanism of photon/ proton interaction that constitutes the bouncing around. I like the point about "no time" for the photon from emission to absorption.
When a photon „bounces“ off of other particles, what actually happens is that the photon gets consumed by an electron and then resubmitted later on, most likely with a lower wavelength. In the end, the last step is an electron on the sun’s surface emitting a photon heading towards earth. That particular photon was actually emitted 500 seconds ago. So what do we consider the actual „birth“ of a photon?
Is the photon after the rebound the same individual as before, or the crashing photon dies and a brand new one with less energy is released after the colision?
In another sense, since C is the limit, not just of light, but of _information,_ a suddenly-dark Sun will occur at the moment we (don't) see it, not "really" at some earlier time.
If we were to assume the “Sun turning off” phrase simply meant that no new photons were produced, wouldn’t that also mean “we” wouldn’t “realise”/see this absence until 170,000 years (and 8 mins 20 secs) as the last photons random walked their way out?
So.... if a photon doesn’t experience any time passing because it is always moving at the speed of light, from its perspective, how does it experience/explain to itself, it’s journey through different energy states (from gamma to visible)?
Dude! Your cool factor went way up when at 3:38 I recognized the Gygaxian tools required for the ultimate, possibly greatest thought-experience played out for the past 45 years.
That hi-five hand slap: You didn't blink! Now that's amazing. Did the shot require many takes or is your self-control really good? Some of both? BTW, Prof. Burton Malkiel appreciated the plug.
ANSWER: Start watching at about 7:00 to learn that by the time a photo travels randomly through the son, and then starts its journey to Earth, over 170,000 years have passed.
I asked about this my astrophysics lecturer many years ago. He said that because radiative energy inside the Su is absorbed and emitted countless time (not being "bounced" or reflected as you say) going down the energy scale from X-rays to visible light, one cannot say it is the same light. I still had my doubt but now I agree with him. Would you say that geothermal energy is billions of years old? No one does but it would be a very similar argument.
The sunlight we get is 6000-8000k. Its the temperature @ the corona. Most of the light we see is ~8 minutes old, it was created in the corona. The light from the core usually gets absorbed before it leaves the sun
So is sunlight old? Or not old? Watch the whole video and let me know what you think! And you can always come find me on Twitter/Instagram: @DrJoeHanson @okaytobesmart
"So why is sunlight so old?" Because photons take a looooong time to escape the plasma of the Sun...
Wouldn't it take 8 and a half minutes for the signal from the remote to reach the sun?!
Age shaming sunlight?! 🌞
You have reached a new low.....jerk.....
What about incandescence of the outer layers? Wouldn't that account for some of the light hitting earth?
The short answer is that it's complicated.
"A balancing act between this urge to collapse and the urge to explode."
*so, like, my life.*
Haha same
@@leannluxcristobal9998 good one
well, you are technically stardust :)
Oh
dont matter what you do, you will still end up dead
~some skeleton from a video
I was really hoping this video would be 8 minutes and 20 seconds long
Well, the "Sun pun" did happened at 8:20
But if you notice, the substance ended at about the 8:20 mark, the parts after that were the epilogue.
Well, the video really ended at 8:20.
@@Arrunell true
@Rajeev Vij no. There is no perspective that moves with c with respect to something with mass. You can't just use the time dialtion formula without thinking.
"How old is sunlight?" Sees upload time: "8 minutes ago". Nice
Sandcastle • you are the top comment
Wrong. Too easy. Guess you didn't watch the whole thing cos you got it all figured out.
Sandcastle • says the one complaining about not getting likes
Tbh i hope youtube makes the upload time always be 8 minutes ago
Lol
"You're only as old as you feel."
-some photon
Haha
@ Whatever you do, don't pick up the soap.
thats would be about 75.... 5 days a week. then 20 ish the remaining 2 lol
is all you comment
"some quote"
-something stupid
Thanks for the enlightenment. I feel SO
much better now.😏
The fact that the density decreases the further out from the core you go, actually adds a bias towards leaving the centre. You're more likely to collide with something on the way back in, so it's easier to go out, even if it's just a minuscule difference.
Not surprisingly, in the photon language, the word for "hello" is also the word for "goodbye."
ALOHA!
@@scQue greetings from the sunshine state lol
So all photons are Hawaiian?
@@tracewallace23 Uke' ot me!
Is it coincidentally also the only word in their language?
Should have used a d8, you can move into those diagonal squares. It's what I always use for a random walk.
Imagine using lame square grids that treat diagonal and orthogonal moves as if they're the same distance.
-- This post was made by the Hex Grid gang
I love this! I miss tabletop rpgs; especially d&d! That random walk demonstration made my day!
Lol
He's not even sarcastic when he says, "Hey smart people".
Yeah, as a dumb person, I always feel kinda left out.
Hello fellow Romanian!
69 likes
nice
@@0dious me too but you are not dumb
@@mikeoxsmal8022 Joe Mama dumb
And now imagine that this does not only happen in the sun, but also every other star. Most of them are millions or billions of light years away and way bigger than our sun.
This means every single photons fights it's way through immense temparatures and unimaginable high pressure for thousands or millions of years only to then travel through space time for another few million or billions of years, only to then reach your retina so you can look at the beautiful night sky. And every time you don't look at the stars, or you do look at them but simply start to blink, all this effort, all the amount of things this Photon went through, is "wasted" for you, because you didnt see it.
It's so tragic that it's almost poetic and beautiful.
Wow unexpected John Cena
So what you are saying is that you don't interact with photons? Because I can't see you John.
@@besmart I'm something of a scientist myself.
pop sci youtube channels made this fact as well known as the capital of New York
Luckily photons don’t interact with time, so to it we don’t exist.
Love your presentation style. It's fun and accessible, but not dumbed down
Oh its dumbed down
@@putraduha3176 well, obviously it is meant to provide the viewer with an overview of the topic and an incentive to do more research by one's self
the mordor meme mightve been a bit excessive but i love these videos
@@putraduha3176 the only not dumbed down version would be the courses required for a university degree
Light taking 8 minutes and 20 seconds to reach earth just shows how far away the sun is. It's crazy.
10.000 years old?
Gives new meaning to the expression, "There's nothing new under the sun."
It’s more like 100k
I bieve he is referring to the approx 100k years it takes for photons once emitted from the core to get to surface. Then it's ~8.min to earth. Gravity!
@@drzecelectric4302 photons don't travel through atoms. They get absorbed by atoms which could then emit a new photon. All of the photons we see from the Sun are 8mins old.
It’s old but it’s still a deadly laser
DEADLY LAZER
Not anymore, there's a blanket!
@@susmitamohapatra9293 Come on, animals, let's go on land!
HackerTV Nope, can’t walk yet. And there’s no food yet so I don’t care
I saw you in a Tom Scott Video and now I see you again ;D
Joe: 100 billion years
Me: AWESOME
Joe: Wait a minute
Me: Oh yeah.. :(
Joe: 170 thousand years
Me: AWESOME
I caught it in an instant even I was surprised to know that I know it's wrong!
Biden?
2:03 That phenomenon of the sun staying stable because its pressure is pushing outward and its gravity is pulling inward is called "hydrostatic equilibrium." That's also how planets like Earth maintain an atmosphere that extends upwards instead of floating away or getting squished against the surface.
I don't know why that one phrase in astronomy 101 stuck with me so well.
Is it really the "same photon" after each interaction with a proton/particle within the Sun? Is that singular photon 170,000 years old, or does it just take 170,000 years from the original reaction of creating a photon, to an equivalent photon being released from the surface of the Sun?
Normally with an actual atom of something, a photon would be absorbed by an electron, which then generates another photon. However in the case of the sun, the immense heat and pressure causes the electrons to separate from their adjoining protons(which is the definition of plasma as a state of matter), which means the photon is actually colliding with a proton. Proton's cannot be excited like electrons and thus the energy is not absorbed, but rather bounces off. This means it is in fact the same photon. Electrons do still exist within this soup of protons though and some photons may become absorbed if they do manage to actually hit an electron.
@@setcheck67 Plasmas simply are states of matter in which SOME or all of the electrons have been stripped away, the key being that positively charged nuclei (Ions) can roam freely. It's a charged gas with high electrostatic interactions. Add to that the "Atmosphere" around the sun which creates absorption lines in the spectrum indicating the specific energy levels absorbed by the atoms and then re-emitted as photons and I'd lean more towards @Rachel Losacco being correct. I get that it's semantics, but she has a point.
It's not the same photon. For each original high energy photon, eventually hundreds of thousands to millions of visible-range photons escape the Sun
@@andredbraxton She asked a question. A question of semantics, but a question nonetheless. So why are you phrasing this as though I'm calling her wrong when she did not provide a statement?
Breaking it down to the deepest level, a photon is nothing more than a carrier of electromagnetism AKA energy. ALL OTHER THINGS CONSIDERED, energy cannot be created or destroyed, but mass can be converted into energy and energy into mass. So to break it down to the most semantic way possible... That photon was created when mass was converted fusing 2 hydrogen atoms to produce helium. That photon continues to exist AS THE SAME ENERGY until it meets another photon and forms an electron - positron pair. Only at that time has it stopped being the same energy. Thus it was born at that instant and "died" when it became mass.
@@setcheck67 No need to take it as a personal attack. I was simply pointing out that through 2 leaps in assumptions (1-in the sun electrons separate from protons, 2-photons can only collide with the protons) you claimed that 'plasma has no associated atom-electron structure and leaves photons with only protons to collide with in the sun' as the basis of your counterpoint. It is a flawed assumption, and the reason I gave you two examples of why that assumption doesn't apply to the case of our sun (1-plasma often has electron-proton structure, 2-There is a photon absorbing atmosphere for photons to traverse as demonstrated by absorption lines in the sun's spectrum)
To your second response about mass-energy conversion. A photon striking an electron in an atom is NOT the same photon that is emitted from the collision. This can be easiest represented by the difference in energy levels in Neon. When struck with a photon of green light, only some of that energy is first released as an orange light photon, then again as another photon as it drops to a lower shell... and then another lower energy photon as it settles into its original lowest level energy shell. SURELY you would agree that such a reaction has nothing to do with two photons colliding and is another way for energy to be transferred from one photon into another different (or in my example, several separate) Photon. Therefor not the same photon from the fusion event, traversing through the soup of plasma, through the collisions with the actual atoms that absorb and re-emit photons of various frequencies when it leaves the surface region of the sun. These photons are "born" in the fusion event, and "die" when absorbed by an electron that gets pushed to a higher shell.
Hey my older sister loves those ball things! I can always hear her playing with them in her room! So sweet ♥️
Giggity.
I know this is semantics, but if a photon strikes a proton and is absorbed (that's why it is losing energy, right?) and then a photon pops out, are we sure it's the same old photon or did that photon "die" and a new one was "born".
It's like the Transporter Problem but for light particles.
It's not just semantics, as more photons are eventually produced than absorbed -- hundreds of thousands to millions times more. The nuclear reactions in Sun produce high-energy photons (MeV to tens of MeV -- Mega electron volts), but the visible photons which escape the Sun have energy of few eV (*). The Sun is in radiative equilibrium (its temperature remains stable), so it eventually radiates all the energy produced by the nuclear fusion -- thus it must radiate many times more low-energy photons for each high-energy one.
____
* eV is a nice little unit -- it's the energy does one electron get from being accelerated with one Volt. For example, photons of visible light have energies from about 1.8eV for red to 3.1eV for violet light. For the same reason, the red LEDs require voltages in 1.8-2V range, and violet laser used in Blu-Ray requires about 3.1V -- they all convert electron energy directly to photons.
Age shaming photons... not cool, man.
Poor photons :(
UNCOOL MAN (oversimplified)
lol Julian Heeck, a PhD student at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, calculated the minimum lifetime of a photon to be 10^18 years, or a _quintillion_ years.
This _alone_ gives photons complete immunity to age shaming.
Source:
Claire Ely. (July 29, 2013) Big Bang Light Reveals Minimum Lifetime of Photons _Scientific American, website_
8:47 Love how the globe becomes dark exactly 8:20 secondes after the sunlight was "switched off"
Huh? I didn't see the globe turn dark at this time...
@@American-Plague it's at 8:47
@@gautamgenani2692 Oh wait...I see it! Nice observation! 😎👍
Dont remember when it started. Still love the sass the globe gives
1:25 is wrong because when you define sunlight as light that originates from the sun you also have to count the light that is created when electrons lose energy and a photon is released, this also happens at the surface so there is sunlight that from our perspective is actually as old as the time it takes to get here.
I wonder if it will ever be possible to age a photon. To say when it was created.
@@DingbatToast Pretty certain it won't be, because of how photons literally don't experience time. If it turns out the universe is deterministic and we got insanely good at mapping/simulating all the particles in our solar system, we might be able to simulate where a given detected photon came from and how long ago, and so figure out how long it took to reach our detector since the moment of its creation. But I doubt that would be possible either for a lot of reasons.
I just need you to know that the hand that came out to high five for your sun pun really resonated with me. I will keep that in my heart and soul forever and think of it when I am sad. Thank you.
"And it is really old! or.. is it?"
I take that as V-Sauce reference
"Sunlight is old. Or id it?"
You just pulled a Vsauce on us
Great video! Another fun fact about the "turning off the sun" thought experiment: If we'd remove the sun, the earth would continue to orbit it for the next about 8 minutes, the same way we'd still see the sun for that period, until the sun's gravitation field would no longer attract it, since gravity also propagates at the speed of light! :)
I like to imagine how that’d look on a spacetime diagram where 3D space is a 2D sheet. A sort of anti-ripple taking 8 minutes to spread out from where the central depression used to be
Probably the best episode! Greetings from Slovakia.
"Imagine you walk out of a tavern and go on an adventure".
Damn but you guys really know your audience.
Ever wonder how Dungeon Masters are made? It's from mothers lulling their kids to sleep with whispers of
*It's okay to be smart. It's okay to be smart.*
FYI to confused people: the orbit animation at 0:55 is really badly incorrect, makes it look like Aphelion and Perihelion are the same distance. Sun should be at one of the foci of the ellipse! Awesome video though!!
#0:31 actually it would take 16 mins 32 seconds... :) this is because the signal to switch of the light still needs to travel to the sun at the speed of light :)
Who says that "someone" is on Earth at all?
@@mcmuinorac5848 probably because they wouldnt be on the sun hitting the switch. And they would also tell you they have hit the switch
Ha! You beat me to it😂
I've had questions about the 'life cycle' of photons since I was a kid and have had no luck getting answers. That is, until this video.
Thanks so much Joe.
Considering all the photons that are "trapped" at any given moment you will understand why the supernovas are so bright - all those photons get released in a couple of seconds.
Omg this video is so good. I love the animations, the analogies, so so so good. Seriously impressed with the upside-down number writing. You are a master.
I hated the jokes, of course, every one of them.
"Please observe posted speeds.
REMEMBER: 300,000 ks/sec is not just a good idea...
...It's the LAW!"
It certainly LOOKS like a law. Would you get arrested if you went faster?
@@DieFlabbergast No
@@DieFlabbergast I mean you dont get arrested
That was a very entertaining presentation, for such a simple topic. YOU GUYS & GALS AT THIS CHANNEL ROCK!!!!
When I first learned this about light, I asked a scientist friend of mine following question: "Is this the reason a supernova is so insanely bright? Is a dying star outshining an entire galaxy simply because 170,000 years of light is all escaping at once?"
I still think I'm on to something here, but he explained that this was actually not correct. I'm sorry I can't explain why it isn't correct because I stopped listening when he told me I was wrong, but I'm sure he's right. But still...
Kudos for little touch of animated sun shining real light at Joe - 0:07
0:42 sneaky little Python reference?
7:40 and Vsauce reference too
oh boy, what a day.
I didn't catch the Python reference.
@@rhoddryice5412 me too,😒
Hi Joe! Fellow Austinite here, and I love your show. At 10:00 of this episode you state that sunlight is responsible for all life here on Earth. Isn't that incorrect, when extremophiles have been found in complete absence of light under the Antarctica ice cap, in the sea floor of the Marianas trench, and even several thousand feet below the Earth's crust?
Great question. The jury is out on where/how life originated. If it originated around deep sea vents then you're correct in that not all of life depends on the sun, but evolution allows plenty of time for life to migrate to extreme environments, adapting to them, so it could be that life originated in tidal regions using photosynthesis and then migrated from there, slowly adapting to other means of energy production like radiosynthesis or chemosynthesis (in which case it still depends on ancestors that relied on the sun). If we find life on Europa or Enceladus, that might strengthen the idea that life indeed first arose on Earth around deep sea vents.
Phylogenetics is the study of how life branches out as adaptations occur, and it allows us to compare DNA/RNA to try to understand the common point of origin (as all species share at least some common DNA/RNA). Scientists are still looking, but this is the field that's most likely to identify the earliest lifeforms. As an example, Methanopyrus kandleri-a form of deep sea bacteria capable of chemosynthesis-diverged from the common ancestor of the everyday bacteria Staphylococcus Aureus 4 billion years ago! Given life on Earth is anywhere from 3.8 to 4.2 billion years old, that's astonishingly close to the origin of life, but there's no way to know the exact characteristics of this ancient ancestor, only that these two genetic lines diverged way back then.
If you want to try this out yourself, go to www.timetree.org/ You can even try something a bit more fun, like the divergence between humans and octopus.
I’m disappointed that you didn’t mention when the 8.5 minutes were up and we lost our sunlight 😅
Look at the earth at 8:46
@@DarkRay12345 ooh thank you! I didn’t see that, that’s actually even better
If you’re going to say photons aren’t slowed by the medium in which they travel, then you really need to define “slowed.” To me, it seems that to be considered slowed you’d need to reach your destination later-and have less energy when you reach said destination-than if your path was clear of obstacles.
Let’s use a human example. You’re standing at one end of a rectangular building lengthwise, and in front of you is a large maze. Your task is to get from your end of the building to the other at a constant pace. However, you’re given an option: you can choose to make all the boxes disappear.
If you stick with the maze option, you will travel at the same “speed,” but the time it takes to get from one end of the building to the other is something like an hour, and you feel physically drained by the end. But if you go with the no-maze option, you’ll arrive at your destination FASTER and with MORE energy. Even though you’re walking at the exact same speed, one option is faster while the other is slower.
So by definition, a photon is slowed by the medium it’s traveling in.
The Bill Nye energy in this particular video is extremely high. Love it!
I enjoyed this video (and your others), however, at 1:43, it's a bit simplistic to say " light travels in straight lines from the Sun to us and that is why we cast a shadow on a sunny day". Yes, light for the Sun travels in straight lines, but its angular diameter in the sky is wide enough that light rays can cross when objects cast a shadow on the ground, so it is an "extended source" of light. That is why shadows we cast on the ground actually have an umbra and a penumbra, just like eclipse terminology. The umbra is created from the light rays coming straight down and casting the shadow and the penumbra is caused by light rays that cross. That is why in a solar eclipse, as the crescent phase gets thinner and thinner, the light rays become linear when in line with the crescent. So shadows cast at an eclipse change! Shadows have sharp edges with in-line with the crescent and have fuzzy edges if cast perpendicular to the crescent. Eclipse education is my specialty. I have a video called "What Are Fuzzy Shadows? - How To See Them" on my channel called Solar Eclipse Timer. Check it out. Please get ready for the 2024 solar eclipse crossing the United States again. Thanks. Gordon
The "hesitation of light" was demonstrated by the danish astronomer Ole Rømer in 1676
I love the details of light on his right side when the sun was there ... small details like this is what I really admire
Mr. Stark...I don't feel so good. Right on the dot.
Someone’s paying attention 🤓
I am surprise to scroll this deep to find this comment. I was really expecting the video darkens on 8:47 when he press the universal button
Extremely good explanation on sunlight journey. A+ score
7:41 Hey michael, VSauce here
Photons travel at the speed of light, so they are essentially ageless. It could be a million years since the photon was emitted, but to the photon it was just emitted. Remember, if you are traveling in the 3 spatial directions at maximum speed (c) then you have no velocity left for the time vector. To the photon time has stopped.
i was actually asking this to myself earlier today.. so thank you for your mind reading powers youtube.. i guess
You know that special pleasure you get when a couple of things turn out to be connected? Well thanks for both that and the references. Looking forward to drilling in a bit more.
1:39 is where the video starts.
gotta hit that 10min mark.
0:00 is when the video actually starts
@@0topon Ok Boomer.
@@Omar-em7rl Its a joke
Excellent video and professionally narrated.
Everyone: The Switch is 3 years old
Joe: How old is the sun?
Good work to simplify difficult consepts!
Actually, most sunlight gets created by the high temperatures at the surface of the sun, not by its core.
Where did you get this information? From the sources I see, it's formed in the core.
@@American-Plague There's a lot of semantics going on here, but the photons that arrive here are not "the same" ones the core creates. Check out the responses to the pinned comment if you want more discussion but this "old photon" is more of an analogy than physics. Like how people say that Hawking radiation is created by virtual particle pairs right on the event horizon.
@@sogerc1 And photons are basically just oscillations of electromagnetic fields so in some sense photons aren't even a thing plus there is actually a point of transition thanks to the equation of state and conservation laws where where recombination occurs such that atoms start regaining their electrons with both helium and hydrogen having reacquired their electrons and thus become opaque to light with hydrogen in the outermost layers of the sun having acquired an additional electron to fill its lowest s orbital valence shell as H- Helium is primarily neutral with only heavier elements having higher level electrons stripped from them.
There are lots of things going on inside stars and ultimately a more realistic system will need to be solved via iterative processes since it is a system of partial differential equations.
@@American-Plague Well the photons that get created in the core due to the nuclear fusion reactions make their way out of the sun as described in the video and with every collision give off a bit of their energy to atoms in the sun. This energy is in the form of heat, thermal energy in the vibrations of the atoms and the thermal radiation that they in turn give off is what we see on earth. So yes all the suns energy comes from the core in for of high energy photons but the majority of photos that reach us are from the surface
The old college dorm was named Moore. It wasn’t always so easy to walk into, so when we broke the glass door we wrote that meme on the plywood they used to cover the hole.
Do a video on coronavirus, pal!
Detective Gumshoe, what are you doing here?
@@imveryangryitsnotbutter trying to solve the mystery of this deadly virus, probably 😅
@@muhammadanasurrehman2993 So, slacking off on the job again? You can expect another cut in your salary this month.
I like how 'The Expanse' series renames the Sun to Sol and the Moon to Luna. Most likely this will be necessary when humans begin to populate the solar system.
After watching this video Im going to say ok boomer to the sun every morning
Cool. I learned waaaay more than I expected. And my expectations were high.
7:40
*Hey Vsauce, Michael Here*
I could be making a mistake but I think the statement that photons are bouncing around and loosing energy might be wrong.
The photons must be absorbed by a particle which then release one (or more) photons of lower energy. And the difference in energy is turned into heat (particle's momentum), which in turn can turn back into light (black body radiation).
Either that or I have to review my understanding of particle physics.
07:41
Vsauce music intensifies....
dig.. DING!!!!!!
How can someone NOT LIKE this show? I love it
My 7 year old thinks it’s hilarious that “you are old” too 😂
Ok, the coolness factor just went up exponentially when you broke out the DND dice and grid map!
Oh and Voltron in the bg! 😁❤️😄
It looks like you have the coolness factor and the HOTNESS factor down pretty good!
Smaller stars are emitting more low energetic light (infrared light) and bigger ones more high energetic light (like UV light). How can you describe this with the random walker?
I mean the way out should be far longer in a bigger star and this should lead to more low energetic light (like the IR light).
I expected you to blink at the high five but you didn't. Amazing self control. Or perhaps the sound effect was added later.
I NEVER FLINCH
@@besmart Good Man! Show that camera who's boss.
Really GREAT video! I was intrigued by the numbers, and have tried to "do the sums" regarding the predicted length of time for a photon to exit the Sun's interior in a very simple model (that is, the hugely long time you get!). This is what I did -- I hope it makes sense! Many thanks for your wonderful resources! Stay safe! ;-)
// Radius of Sun (m)
Rs = 690 x 10^{6}
// Volume of Sun (as a sphere) (m^3)
Vs =4 pi Rs^3 / 3
Vs= 1.37605528 × 10^27
// Number of protons in Sun
Np = 10^57
// Volume occupied by a proton (m^3)
vp = Vs / Np
vp = 1.37605528 × 10−30
// Closest distance between protons on cubic lattice (m)
dp = vp^(1/3)
dp = 1.11227445 × 10^−10
// Total distance of random walk from centre of Sun to outside = Rs
// Step-length in random walk = distance between protons = dp
// Random walk formula: "total-distance = step-length x ( number of steps )^(1/2)"
// Number of steps in random walk
n_rw = (Rs / dp)^2
n_rw = 3.84834732 × 10^37
// Total distance of random walk (m)
D_rw = n_rw x dp
D_rw = 4.28041839 × 10^27
// Speed of light (ms^-2)
c = 3 x 10^8
// Time for random walk (s)
t_rw = D_rw / c
t_rw = 1.42680613 × 10^19
// Time for random walk (y)
T_rw = t_rw / (60 x 60 x 24 x 365.25)
T_rw = 4.52127579 × 10^11
T_rw = 452 Gy
The animations were top notch and helped tremendously!
I loved the T-82 reference with big computers! That's what I grew up on too.
Fascinating and well told ... BRAVO!
the last word besides sponsors an d the words "sun pun" was enlightening at 8:20
I would be interested to know the mechanism of photon/ proton interaction that constitutes the bouncing around. I like the point about "no time" for the photon from emission to absorption.
Never knew I needed this. but so glad I watched it!
Loved this video! Nice touch using misconseptions as a tool for learning.
Like how this dude explains things on this channel. Thanks for the awesome info 😊
I love the dnd references! Great job Joe!
When a photon „bounces“ off of other particles, what actually happens is that the photon gets consumed by an electron and then resubmitted later on, most likely with a lower wavelength. In the end, the last step is an electron on the sun’s surface emitting a photon heading towards earth. That particular photon was actually emitted 500 seconds ago. So what do we consider the actual „birth“ of a photon?
Is the photon after the rebound the same individual as before, or the crashing photon dies and a brand new one with less energy is released after the colision?
The passage of time is not zero at the speed of light. It just approaches zero near the speed of light, which is not the same thing.
In another sense, since C is the limit, not just of light, but of _information,_ a suddenly-dark Sun will occur at the moment we (don't) see it, not "really" at some earlier time.
It’s good to know Joe is a fellow DnD nerd
If we were to assume the “Sun turning off” phrase simply meant that no new photons were produced, wouldn’t that also mean “we” wouldn’t “realise”/see this absence until 170,000 years (and 8 mins 20 secs) as the last photons random walked their way out?
So.... if a photon doesn’t experience any time passing because it is always moving at the speed of light, from its perspective, how does it experience/explain to itself, it’s journey through different energy states (from gamma to visible)?
I did not know this. Thank you!. I'll just take a moment to acknowledge the actual light source added in 0:07
Dude! Your cool factor went way up when at 3:38 I recognized the Gygaxian tools required for the ultimate, possibly greatest thought-experience played out for the past 45 years.
This video is about sunlight...
(glowing Sun appears)
I love subtitles
I'm convinced all science tubers have some sort of group chat where they agree on working on similar videos lol
That hi-five hand slap: You didn't blink! Now that's amazing. Did the shot require many takes or is your self-control really good? Some of both? BTW, Prof. Burton Malkiel appreciated the plug.
Thank you so much for uploading this video. It is helping me get through the pandemic!
Nicely explained
ANSWER: Start watching at about 7:00 to learn that by the time a photo travels randomly through the son, and then starts its journey to Earth, over 170,000 years have passed.
I asked about this my astrophysics lecturer many years ago. He said that because radiative energy inside the Su is absorbed and emitted countless time (not being "bounced" or reflected as you say) going down the energy scale from X-rays to visible light, one cannot say it is the same light. I still had my doubt but now I agree with him. Would you say that geothermal energy is billions of years old? No one does but it would be a very similar argument.
The sunlight we get is 6000-8000k.
Its the temperature @ the corona.
Most of the light we see is ~8 minutes old, it was created in the corona.
The light from the core usually gets absorbed before it leaves the sun
I read about this in an Arthur C Clark book and it blew my mind
What do you call a random walk to the bathroom?
Brownian motion.
Loving the Hulk byline in the captions when you're talking about gamma rays 😂