Physics Girl - 2016-03-15
This episode is brought to you by Squarespace: http://www.squarespace.com/physicsgirl When light passes through the universe and is redshifted by the expansion of space itself, how is energy conserved? The stretched light has a longer wavelength and therefore a lower energy. Is energy conserved? If so, where does it go? Many thanks to Sean Carroll for his wonderful description of this question: http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ More resources: http://motls.blogspot.com/2010/08/why-and-how-energy-is-not-conserved-in.html http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html Help us translate our videos! http://www.youtube.com/timedtext_cs_panel?c=UC7DdEm33SyaTDtWYGO2CwdA&tab=2 http://physicsgirl.org/ http://twitter.com/thephysicsgirl http://facebook.com/thephysicsgirl http://instagram.com/thephysicsgirl http://physicsgirl.org/ Creator: Dianna Cowern Editor: sefd.com , Jabril Ashe Writer: Sophia Chen Gravitational Wave Animations: LIGO Visuals: Pixabay.com Music: APM and YouTube
Physics girl is conserved on my heart
I guess we can start making those perpetual motion machines now then :)
+koseq7 That would be the opposite of perpetual motion xD
I found sancarn
Maybe inside a black hole but I don't think anyone would venture there.
No. In earth, energy is conserved almost completely.
"The energy is simply...lost."
Yeah, nah. I don't think so.
Nobody care about what u think ! Show me a counter argument
@StupidityKiller - u talking to me? no counter argument to my statement. because logic is true. If universe is infinate, then conservation of energy is false by definition. your name tho
@AA CC - Hhh you said i don't think - that energy is simply lost - you do not give a logical explanation nor even an argument to support what yo u say.
Logic ISN'T True, you cannot equal Truth - that have philosophical roots and it's very meta - with logic - that it's, by definition, systematic study of the forms of inference.
"If universe is infinite, then conservation of energy is false by definition." - well first this isn't a proper argument bcs of "if", you don't know if the universe is infinite, and 2nd you only doesn't logically imply the other
@StupidityKiller - yes it does.
The Frog in the Well is similar to Plato's cave allegory. :)
It is pratticly the same, there are a lot of variants of philosofical thoughts, some of them are a modernized version.
+Jordan Munroe exactly
Though it covers a smaller total analog (sheltered individual vs sheltered society) so it is a lot simpler to use to convey this message. :3
This topic is gonna need a lot more videos.
+Boris Svetiev a LOT. Like at least 20. I'm serious.
This video is making me uncomfortable. 😰😷
+Boris Svetiev If this was part 1 of 7ish I would subscribe JUST to see the rest! All I know is that my brain hurts and I'm now convinced the universe is somehow broken. Gee thanks.
+Samsul Hoque Just be in well.
SerenityReceiver From what I understand, many physicists believe that energy isn't fundamental in this universe - it can be both lost and introduced and that what is actually fundamental is information - that is preserved within the universe. Kinda makes the universe sound a bit like a program. Maybe that's what it is.
Throwing a wild idea here : Could this energy loss actually be "stored" in dark energy ? Or are these two things totally unrelated ?
@Goran Micevski
"they are just theory"
No. First of all, I get so tired of people saying "just a theory" as though a theory is just a hypothesis.
Secondly, the retreat of galaxies from our location in the universe is measurable (including by the red shift) and is occurring equally in all directions from us. So it is not a 'theory' but an observation and a fact. Same for 'dark energy'. There is something that is driving the expansion of the universe faster than it should be from our calculations using what we do know about the amount of energy disbursed in 'the big bang'. And, we also know there is more gravity acting in the universe than can be accounted for by the mass/energy which we can see and measure. Since we can't 'see' them, but can measure them, we know they exist (the extra energy and gravity), but label them 'dark'. Thus they are also an observation and a fact.
67 replies?? I'm not reading all that!
My guess would be that this energy, like heat energy is simply lost. It's all part of the long, drawn-out death rattle, leading to the heat death of the universe.
@Sean Shubin My thoughts as well
The answer is YES.
It’s complicated though, everyone is born with all energies.
🐚
We don’t actually know very much about dark energy but I’m pretty sure it speeds the expansion of the universe but maybe it does somehow play a roll or maybe there’s another type of material that we don’t know about.
1:37 Half Life 3 confirmed.
+Ressurrectify legit
The energy isn't lost. It goes into fringe physics theories on the Internet. :)
Darth Wedgius go to hell loser
CONFORM
Its been a while since a science video has made me think this hard. Thank you for the revelations.
I think the term should be relevations.
"Is energy always conserved?"
Not according to sign above the light switch that says "to conserve energy, switch off when not in use." (I leave it on to see how long before the universe ends).
The Koch brothers thank you for your diligence as a consumer. They'll be using your contribution toward this effort:
http://www.foxnews.com/politics/2017/06/25/koch-brothers-group-set-to-give-up-to-400-million-to-midterm-candidates-who-go-big-on-tax-and-health-care-reform.html
if energy can get lost it also could be possible to create energy
+Silentsouls Watch sixty symbols videos about the speed of light or special relativity in general.
Light does not "seem" slower when we are drifting away, thats not what happens when it redshifts. the speed of light will always, in any circumstance or frame of relevance, appear to us moving with c (ca. 300'000'000 m/s) in the medium its travelling through. Even if you self are travelling with 99% of the speed of light yourself, and you send a lightbeam ahead of you, you will see the lightbeam travel away with the speed of light.
How come? time and space dilation. Time for you and the space your frame of relevance takes up fundamently change. your time will go slower, and distances will get shorter, allowing the lightbeam you sent out to actually reach everything in a time relative (hence relativity) to you as if you were not moving at all.
If you look for it you will definitively find peer reviewed papers on that, just look for special relativity.
+Silentsouls For sure Einstein wasn't right, what we don't know is where is he wrong and what's a better answer. For now we accept what he discovered because it works at this point. That's what science does.
+UniQuE TV Hmm...
Possibly by compressing the Universe. But that is just too hard.
Imagine that space is air. The less pressure the air is under the more it expands and it will seem like it is cooling down because the energy has to be spread through more space, but at the end the energy is conserved. If the air remained the same temperature, you'd be creating energy.
*enraged entropy sounds
I think you need more videos on the matter about energy not always being conserved. It's a very interesting topic that can get real confusing real fast. Just look at the comments
Hmmm.... I wonder if the expansion of spacetime can somehow account for the loss of energy. That this perhaps somehow relates to dark energy...
For example that, light interacts with some particle weakly, loses some energy that causes it to red shift. And at the same time, spacetime gets a small kick and expands.
+HexerPsy Or if the stretched out wave is "longer" and as such it just spread out the same amount of energy over a longer portion of space with lower power.
Nothing like a young pretty girl to help sell some ideas dressed up in assumptions.
Sorry, but there will be no More "Happy Physicsing" for me, now that you've gone and ruined conservation of energy. :-( Sad Trombone.
+USWaterRockets Join us chemists! We love conservation, we even pretend atoms are conserved!
Gareth Dean LOL 😂😂😂😂
/Plays sad violin music while eating cherry pie and cream.... We care, we really do. I also lie occasionally for effect :P
what if you connect a very long spring between two galaxies that are moving away from each other because of the expansion of the universe. this spring would heat up, like when you stretch a rubber band. is this creating energy?
Huh, good question.
Wow
That's a great question
the answer is no, you are converting mechanical energy into heat, NBD. Also its completely impossible to do that anyway.
> is this creating energy?
Yes, I believe it is.
Ask your favorite search engine about "Extracting energy from the expanding universe: can we avoid the heat death?" (in quotes).
If you send out a pulse of 1 second of blue light, by the time it's red, the pulse lasts for about 2 seconds, doesn't it? So the light is less energetic, but there is more of it. So no energy is lost?
+David de Kloet I believe 2 seconds would be describing the distance between photons, not the number of photons. So it would be the same "amount" of light.
+CodeKujo does that mean, if you send 20 watts of blue light you get 10 watts of red light?
@Abhilash Gandluri I think it's actually worse than half. You have half the energy (Joules) delivered over twice the time, which means one quarter the power (Watts)! So 5 watts of red light.
@Abhilash Gandluri Think inverse square law.
So... what you're saying is the EM drive is legit???
4:45 WOAH ITS PLATO'S CAVE happy philosopy moment
The claim that energy is not conserved during cosmological redshift is something that many physicists would disagree with. Although some people say that the energy is "lost", many others say that it is transformed into the gravitational energy of space-time.
+Physics Videos by Eugene Khutoryansky but wouldn't the soace-time be expanding just as quickly if the light weren't in it? Or am I confused?
yeah because eugene is totally not a physicist and totally hasn't made physics content that span hundreds of hours and goes into much greater detail than physics girl lol
"Not traveling through a medium? Most of space is empty?" Show me a pie graph that shows a % of the universe as empty/nothing.
Then the gravitational energy should be increasing constantly. But is that gravitational energy transferred to another form of energy?
You need to write down a formula for "gravitational energy of space-time" if you want to have a solid argument, not hand-waving.
The question of whether energy is globally conserved is more difficult than many think, since there is no unambiguous way to define global energy in a curved space-time. (You can do it in flat, Minkowsky spacetime).
Your hair is gorgeous.
I don't even care, I just want to hear her voice.
I'm so in love ♥
The only reason I watched to the end was because my fingers were busy rolling a joint. Hope that helps your survey.
I am soooo glad when I see girls like you <3 I hope you'll encourage girls to not be afraid about sciences :)
very nice video BTW ;)
Hey Physics Girl. You've overlooked one thing about photons in an expanding universe: The energy of the photon changes only depending on the reference frame. Seen from the point of view of a reference frame that compensates for the expansion like maybe the galaxy it originally came from or the photon itself (I haven't thought it through that deeply to find out which would be the correct reference frame) its energy would still be the same, right? This is relativity and you're handling it with absolute terms here...
Lukáš Fireš well? Spit it out
Lukáš Fireš dark energy
Connor Dow, your saying that as the photon redshifts the energy is constant because the light would last longer... A atom emits blue light for 1 second in a non expanding universe, while the same atoms light now lasts for 3 seconds and is redshifted in a expanding universe?
Szabii[Editor] you could also consider the time between the photos hitting the solar panel to take longer, so instead of having a million photos hitting in one second, after a the red shift, only half the rate or 500,000 photons would hit per second. The duration is longer but the total number of photons is conserved.
Connor Dow
No red shifted ligth will produce no energy even if it keep on hitting the panel for 1000 years.. look up photoelectric effect.. and she also give in the video the energi for a photon:
E = hc/lamda
Could the "loss" of energy actually just be transferred to fuel the expansion???
I agree with the Dilution Energy Theorem. As space expands the energy density decreases which is evident by the increase in wavelength. Energy is like icing on a cake; for a fixed amount of icing, which cake is going to have more icing per slice, a small cake or a big cake!! I WANT SOME CAKE!!!!
5:12 My god that audio quality lol
Fascinating! Dianna, I have a question for you, though. If energy really is lost as light becomes red-shifted when traveling through the expanding universe, does that mean that if we "ran the clock back" and "shrank the universe," energy would be created as light blue-shifted? Also, since we know that as the universe expands, light energy is decreased (red-shifting), does this imply that expanding space itself is a form, or result of, the conservation of energy?
I am so glad you made this video. I spent many hours talking with an astronomy professor about this very topic a couple years ago and the question always bothered me.
No pun intended, but going from "space is expanding" to "therefore the laws of physics aren't constant" seems rather a stretch to me. I'd like to see a video in which you explore that more fully, because I don't see that conclusion necessarily following from that particular premise.
This video arrived in my subs at the perfect time to (maybe) help settle an argument ;) Thanks!
OMG. Can't wait to tell my friends this. : )
May be, the energy lost by photos gets added up as "the dark energy" that works in expanding universe
when I started this video there was 15 seconds advertisement.
then at the end of the video there was advertisement too.
rly, you get dislike.
AHA-moment at 1:17, Great video!!!
what if the "lost energy" is converted into some form of dark energy because it isn't detected
You might possibly be right.God knows,my friend.Merci beaucoup,mon cher ami,and God bless you.
I've just completed the survey, and of course I've put Physics Girl as my favorite PBS digital studio show !
5:02 Or zoom in :)
"The law of conservation of energy applies on our own well". Life in one sentence. For the curious, open minded and humble :) .
I did the survey! I told PBS that you were my favorite PBS show :P
Wow! Very interesting question! Even though we all heard of redshift due to expansion, the question never came to mind as to consider conservation of energy.
Thank you so much for doing what you do. I love your explanations!
that was a good one
As the lightwave is redshifted and stretched longer, doesn't it mean that the total amount of energy is same but the energy of a particular length is decreased?
This video confused me that I had to watch it 3 times in a row 😥 happy physicsing
How do you know energy isn't conserved?
Was there a test or experiment to confirm this? Isn't possible the energy is conserved in a way we can't comprehend or understand?
+SergeofBIBEK exactly what she was speaking of, it applies in our own well, it's possible it's not convserved and it's also possible that it is but in a way we don't know of
@Sean McDonald But she seemed to definitively say that energy ISN'T conserved.
yea,because she's just saying that's the conclusion she drew from it, though i must say she should have been less certain
Thanks for blowing my mind. Just when I thought I had a basic understanding of physics, thinking, the weird stuff is in quantum physics, you went ahead and destroyed my happy place.
If an expanding universe decreases the energy of a photon, does an shrinking universe increase the energy of a photon?
Yes!
Also motion of the source towards you blueshifts the light as well.
the universe is not expanding
Doppler effect
Veritasium - 2016-03-15
Second!
Rohan Deshpande - 2018-09-26
What if universe was contracting.. will energy increase
Phenomenal Physics - 2018-09-27
@Rohan Deshpande maybe.... Ugh light is so wired it does not even follow physics laws properly
TheOnecosmos - 2019-11-14
@Momchil Momchilov ''The space created from nothing'' is nonsense.
Momchil Momchilov - 2019-11-14
@TheOnecosmos Well, that is the only explanation I know for redshifting. Forces cannot redshift light, but expanding apace in every direction (more space from nothing) can.
TheOnecosmos - 2019-11-14
@Momchil Momchilov Yes expanding space redshifts light and conversely, contracting apace blueshifts light, it means that the energy goes into the Universe's expansion itself, in the form of work, energy is always conserved!. But the spacetime is not created from nothing! peace.