Hubble's law | Scale of the universe | Cosmology & Astronomy | Khan Academy
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- Опубликовано: 27 авг 2024
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Hubble's Law. Created by Sal Khan.
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I just imagine Edwin Hubble casually sipping his coffee and checking out all the cool redshifts in the galaxies, then suddenly turns his telescope to see a blueshift in Andromeda and spews all over his papers.
underrated comment
@@creedorian very underrated comment
She asked me why I was blushing. I replied "I'm actually just moving away from you very, very quickly"
This is brilliant 😂
Niice
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I somehow forgot the account password. I appreciate any help you can offer me
@Zaiden Ignacio instablaster =)
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Thanks man! Very helpful!
With the respective growth of space itself, both apparently inside us and outside our very bodies, wouldn't we in that case have the atoms in our bodies be expanding at a similar rate, but also being compressed, as space itself is expanding, so all empty space is expanding... including the empty space inside our bodies?
THANK YOU SO MUCH....
THANK YOU FOR THE CONCEPT SIR
Thank you.
Very helpful for my exam.
doesn't he mean 7 milliion lightyears at 9:06 ?
Expansion has to happen from the inside out not from the outside out
really informative video,all clear,thank u so much for making this video
really helpful! thanks a lot
all velocities are apparent(relative) aren't they. So how would the expanding universe be any different?
Hubble's Constant can be easily calculated using ONLY the speed of light (C) and Pi 2 X a megaparsec X C, divided by Pi to the power of 21 = 71 K / S / MPS. This equation comes from the "Principle of Astrogemetry"
If the galaxies aren't moving, but rather space is stretching, what is sticking the galaxies to space so it can be carried along with it?
Yes, good point, even relative velocities can't beat light speed. I don't know the answer I'm afraid but something tells me when it's a point in space relative to a point in space this might not apply, otherwise it would be space bending spacetime to preserve light speed. Not sure.
@Melthornal We would reach it. Although space is expanding, gravity is much stronger at "close" distances - galaxies are not expanding.
but still its very weak , integral multiple of G
typo at 8 mins
m = milli = 0.001
M = Mega = 1 000 000
Still very clearly explained.
7 minutes and 52 seconds
For everything to move away at an accelerating pace as distances increase would indeed require that the distances between atoms themselves increase at the same rate; but if that's the case, then the fabric of space itself is expanding at that rate... so the comparable distances between objects would be the same. Isn't that the case?
yes but we can't forget about gravity wich in shorter disnces is stronger than the expansion
@@antoniomoral4831 Valid point.
@@chissstardestroyerPlus, forces within molecules are WAY stronger than gravity
@@twopolaar599 Yes; that's true too; especially given that the sizes of the items involved would inevitably lead to such a difference in type of balance.
Things moving away in every directions RADIALLY from each other’s gravitational fields in the vacuum, so further it goes lesser it’s pulled back by each other.
No wonder it accelerates, as the gravity itself is the acceleration.
A matter moving away from the center of the universe in constant velocity linear motion, but the pull from the universe center remains, yet it’s moving away RADIALLY from the center so further it goes the “density” of the gravity pulling it back decreases. Hence it accelerates in the opposite direction.
Very simple.
Forget about dark matter and stuff.
So does that mean the universe will stop expanding at some point?? Or did I misunderstand this..
That can’t explain the acceleration. A weakening of a force decelerating an object isn’t the same as an object accelerating. It’s merely decelerating at a slower rate. That’s not acceleration.
in any local area of space anything can be happening. these laws/rules are valid at the large. For e.g. if a comet moves towards earth, it is not violating the idea that everything (in general and in the large) is moving away from everything else (in general and in the large).
What would be a good career field to get into for studying space ?
am i the only who when faced with a problem like this and can't bring myself to understand it for a while but then i finally get it, some tears just run down my face?
I assure you, you ain't the only one.
@@manprithsingh5195 I am pleased to know I'm not.
space isn't stretching, the amount of time between the objects has increased
Hi K A
Thanks for the Nice and informative Video.
I have one major issue I am grabbling with ..ok here it is
Hubble's
Constant is basically the Gradient of Reccession Velocities of Galaxies
against their distance from the Observer in Megaparsec.
OK What has
the Inverse of the Gradient (1/Ho) got to do with the Age of the
Universe. OK yes the inverse is a Unit of Time but no one has explained
what this constant is and why it is the Age of the Universe. There are
many Linear Relationships in Physics with known Constants, for example
Plancks Constant, but I am not going to pin Plancks Constant on some
Major Cosmology or other Physical datum. I dont see where you guys are
getting the Inverse of Hubble's Constant to be the Age of the Universe..
Where is the Maths.
Hubbles constant is expressed in km/s*mpc. You notice you have 2 units to mesure distances: km and MPCS so if you put the km in Mpcs you get a result in s ^ -1 if you then find the inverse of this you get 14 Million years, approchimately the time we now know the Big Bang occured. If you go back in time the galaxies that are farther away will get closser at a faster rate and the ones that are closer will get closser to us at a lower rate. If we go back 14 million years we would all be in a single point: just before the Big Bang.
@analog ❤️ Hubbles constant is expressed in km/s*mpc. You notice you have 2 units to mesure distances: km and MPCS so if you put the km in Mpcs you get a result in s ^ -1 if you then find the inverse of this you get 14 Million years, approchimately the time we now know the Big Bang occured. If you go back in time the galaxies that are farther away will get closser at a faster rate and the ones that are closer will get closser to us at a lower rate. If we go back 14 million years we would all be in a single point: just before the Big Bang
What program is he using?
MOKNEY
@@emelyarye2641 yo, thanks for the quick reply!
@@SomeSteven np
Just did little calc. Rougly at distance 13,85 billion light years space is stretching faster than the speed of light then. So i doubt we will see any further as we see now (which was stated in one of the previous videos).
@Melthornal Yes the escape velocity of our own galaxy ( the milky way) is greater than that of the velocity of voyager 1. It will never leave our galaxy.
So much for gravity
Tell us about gravitational red shift. Explain why our sun exhibits red shift.
@Fuxy22 Good question! The speed of light is theoretically a maximum. I dunno the answer :/ But I would guess once it gets to the speed of light it can't go any faster... Does anyone know?! :)
If like Hubble we interpret this redshift due to the doppler effect what actually happens is that the doppler formula is addapted, due to restricted relativity. The velocity and distance are not proportionnaly linear anymore and so it can never reach the speed of light. However this are not real distances travelled by galaxies, it is space time that streches. Also the hubble law also doesn't apply to big distances because H0 varies in time. The constant applies to distances in the moment and if we look at a galaxie that is far away we would be seeing the galaxie as it was in the past because light takes time to reach us.
Sphere?
So, we are assuming the velocity is constant? Or has that been determined?
So, using hubbles constant, aren't galaxies a certain distance away moving faster than the speed of light?
yeah but the light from them hasnt reached us yet so we cant confirm. (I, Think)
Realistically, from Earth's perspective the fabric of space time between earth and and the galaxy in your question is being "stretched" faster than the speed of light by dark energy, but not actually moving faster than the speed of light themselves.
The strength of expansion seems to be overcome by forces like gravity and electromagnetic forces that hold atoms together. Our atoms in our bodies won't be stretched from universe expansion (only a miniscule unnoticeable amount). Same goes for the atoms that make up the planets and galaxies. Expansion acts on everything surrounding galaxies but not the galaxies themselves(only a miniscule amount) Gravity from these galaxies seems to stop the space time from 'universe expansion' as well, gravity is a strong enough force that it overcomes expansion and keeps the galaxies local spacetime "pulled together".
Imagine galaxies are beads glued to a stretchy fabric. As you stretch the fabric, the bead itself wont be stretched but other beads around it will stretch proportionately to each other (like Hubble's Constant). The fabric of space time isn't "pushing" the galaxies away, so the galaxies aren't actually moving *through space* faster than the speed of light, it's the fabric of space time around them that is growing and "stretching" around them faster than the speed of light.
It seems that it is dark energy expanding space time that is breaking the speed limit rules, and not an object moving through space faster than light.
@@k1ng724 We will never see the light from those galaxies If the expansion of the universe overcomes the speed of light. The light will be trapped at an event horizon (The exact point/distance the space time expands faster than the speed of light). We will see the light from these galaxies for a brief period when it reaches us then it will go out like a candle. (If the galaxy was ever outside of the event horizon of expansion in the first place)
@@k1ng724 We will never see the light from those galaxies If the expansion of the universe overcomes the speed of light. The light will be trapped at an event horizon (The exact point/distance the space time expands faster than the speed of light). We will see the light from these galaxies for a brief period when it reaches us then it will eventually go out like a candle. (If the galaxy was ever outside of the event horizon of expansion in the first place)
the expansion of the universe creates drag on mass, thus mass is moving away. Anything massless has no drag on the expansion, so is picked and carried with the expansion at the speed of c.
Sorry, where does the "Plus or minus 3.1" part of Hubble's constant come into play?
Their not on the surface their in space that's the difference
@runawaybg That's because the force caused by the gravitational attraction (acceleration) between the Milky Way and Andromeda is bigger than the stetching at this distance.
that is true but also galaxies have a unique speed that can accelerate the expansion or diminish it. Normaly this velocity is nothing compared to the expansion but in andromedas case it is predominant because andromeda is relatively close to the earth and with the help of gravity it is getting closer to us. This unique velocity is at an average of 600 km/s. Andromeda and the milky way (our galaxy) will collide in about 4 500 million years at 120 km/s
How to prove Hubble’s Constant like how did he come up with it
He did it by measuring many distances and velocities with the helps of Humanson. He measured at the time 558 km/s mpc
I do wonder how much the fact that light redshifts due to distance travelled, how much that effects it
I'm wondering if its perhaps the explanation
as I saw one likening red shift to audio Doppler effect saying the road was stretching away from you
does this come from the universe not having definitive points to measure from?
Hi Mr. Khan. Your videos have inspired me to make my own. Not quite up to your level of quality yet, but they're getting better over time. Here's what I made about Hubble's Law a couple of months ago: watch?v=9ZpaBqiMwi8
It means atoms are also expanding?
omg... it is a moment of realization ... i read Space is also expanding several times but never quiet registered how that affects two points upon the third... that is huge! Still im not quite following how Hubbles constants roughly 70.6km/sec//mega parsec? Anyone ?
No no mater can move faster than light, and no mater with any mass can move as fast as light. this boils down to Einstines famous prof E=mc^2 for light or
E^2=(m0^2*c^4)+p^2*c^2)
where E is energy m0 is the mass at rest c is speed of light(vacume) pis momentum
from this pathagorean equation you can tell that nothing can reach the speed of light because the hypotenuse of the triangle is always longer than the longer leg.
I understand how this works but I still can not get my head around space expansion bast C and it affecting mass.
Well i think it might have something to do with space itself expanding? ie distance traveled over time would not change? but then why would we see the red shift? i don't know and it starts to hurt my head! I think i need to go to the library and get some good new physics books.
we would see the redshift because the expansion of the univers will make the distance between galaxies grow and this will make the light wave strech causing the wavelength to increase. The wavelength growing is the redshift.
great video
Is a lightyear a good constant rule of measurement of distance in space; or does it change at all, especially with the universe itself growing constantly and accelerating in its growth, Mr. Khan?
Yes because we will never reach a higher speed than light speed. If like Hubble we interpret this redshift due to the doppler effect what actually happens is that the doppler formula is addapted, due to restricted relativity. The velocity and distance are not proportionnaly linear anymore and so it can never reach the speed of light. However this are not real distances travelled by galaxies, it is space time that streches. Also the hubble law also doesn't apply to big distances because H0 varies in time. The constant applies to distances in the moment and if we look at a galaxie that is far away we would be seeing the galaxie as it was in the past because light takes time to reach us.
@@antoniomoral4831 Aside from slight misspellings, such as "galaxie" for "galaxy"; those are very valid observations.
what would happen to a point in space that is moving away from earth at a speed greater then the speed of light? Would that determin the boundry of the observable universe?
If like Hubble we interpret this redshift due to the doppler effect what actually happens is that the doppler formula is addapted, due to restricted relativity. The velocity and distance are not proportionnaly linear anymore and so it can never reach the speed of light. However this are not real distances travelled by galaxies, it is space time that streches. Also the hubble law also doesn't apply to big distances because H0 varies in time. The constant applies to distances in the moment and if we look at a galaxie that is far away we would be seeing the galaxie as it was in the past because light takes time to reach us.
So if we were to get in a spaceship and go 70.6 km/s, we would never be able to reach something that is a megaparsec from our initial point? Since Voyager is going about 60 times slower than this, does that mean Voyager has no hope of ever going any significant distance relative to the rest of the universe?
Voyager 1 is travelling at 62,140 km/hr which is about 170 km/s, so yes it would be gaining on Andromeda if it was heading that way.
I don't think the expansion of the universe is given enough credit for universal laws
So as an object moves away from me, it accelerates according to Hubble's law. So it must have s force?? What does this do for Newton's Laws?
I don't think that they are acctually moving, galaxies are still in a 3 dimesion sheet called space-time that can not only bend but also strech. Dark energy is responsible for this expasion.
I guess thats the whole reason then that we see background radiation at that distance?
so if the space is stretching, that means we are stretching too... creepy
this would make for some nice homework excuses.. 'sir, all the letters on my essay just started drifting away from each other :|'
hahhaahahahhh when?
@zbe8 what unit did you use for D? km?
But it's not
It goes approximately 0.0000000000008 mph or something like that if it was in a race with a snail,bamboo, the snail would win and it’s a one meter race! And it would take 14MILLION YEARS to reach 1 meter
It can go faster than the speed of light because it's just an apparant velocity.
If like Hubble we interpret this redshift due to the doppler effect what actually happens is that the doppler formula is addapted, due to restricted relativity. The velocity and distance are not proportionnaly linear anymore and so it can never reach the speed of light. However this are not real distances travelled by galaxies, it is space time that streches. Also the hubble law also doesn't apply to big distances because H0 varies in time. The constant applies to distances in the moment and if we look at a galaxie that is far away we would be seeing the galaxie as it was in the past because light takes time to reach us.
Andromeda isn't moving away form earth. So its wrong
galaxies have a unique speed that can accelerate the expansion or diminish it. Normaly this velocity is nothing compared to the expansion but in andromedas case it is predominant because andromeda is relatively close to the earth and with the help of gravity it is getting closer to us. This unique velocity is at an average of 600 km/s. Andromeda and the milky way (our galaxy) will collide in about 4 500 million years at 120 km/s
Türkçe altyazi bir noktadan sonra bitiyor :(
im gonna go and assume it's Dr. Khan...
if space is stretching outward are the particles in my body moving away from each other?
If i remember correctly, for particles that are attracted to each other, the effects of the expansion of space are reduced. As the particles in your body are bound by electromagnetic forces, they are kept in place, whereas distant galaxies have extremely small gravitational forces on each other, so the expansion of space is enough to cause them to move apart, I wouldn't say I know how strong the force needs to be to overcome the expansion of space though.
can someone tell what software is being used for this presentation?
Microsoft paint
is it true ? i am wonder about astronomy
But why, andromeda galaxy shown blue shift, that mean its going closer to earth, while other galaxy stretching away??
Yeah milkway and andromeda are bound by force of gravitation, they are said to merge together in future.
galaxies have a unique speed that can accelerate the expansion or diminish it. Normaly this velocity is nothing compared to the expansion but in andromedas case it is predominant because andromeda is relatively close to the earth and with the help of gravity it is getting closer to us. This unique velocity is at an average of 600 km/s. Andromeda and the milky way (our galaxy) will collide in about 4 500 million years at 120 km/s
Can someone clarify why according to Hubble's law everything is moving away, and the andromeda galaxy and the milky way are supposed to be crashing together in some couple of billions of years
Because they are relatively close to each other. The galaxies "move away" from each other on larger scales, for example comparing two big chunks of the universe, rather than two individual galaxies.
I'm Canadian, so, thank you and sorry
No worries!
a galaxy is billions of stars but it also has a much greater mass of nothing (space) so the milky way could pass straight though with no crashing involved.
Newtons Law of Gravitation bro.
Every interstellar object in NOT moving away from Earth
I thought the same thing at first....but whats the definition
I know but it's wrong
No that's not correct
nicw
By 60 times slower I mean 3600 times slower. o.0
@zbe8 haha that isnt calc.
magenta point why lmao
v=HoD
first
Waste of time.. dont watch this video
why?