Professor Dave Explains
Professor Dave ExplainsRelativity comes in different flavors, as it happens. We spent some time looking at Einstein’s special relativity, so now it’s time for the general variety. This is all about the geometry of spacetime, which curves around massive objects. This was a huge update on our understanding of gravity, so get on board!
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43 Comments
@ADITIGAVHALE-z6z
03/07/2025 - 11:16 AMI am literally obsessed with the intro…………😂😂😂it's stuck in my mind😂😂❤
@ajvg1037
03/07/2025 - 11:16 AMThis explains light can bend around an object, it doesn't explain the force that pulls everything down to Earth's core.
@TejasPatil0
03/07/2025 - 11:16 AMI am getting sadder every second
@chiangchengkooi9791
03/07/2025 - 11:16 AMMost will explain how but not why mass can distort space and time around.
@mehdizangiabadi-iw6tn
03/07/2025 - 11:16 AMGravity of the curvature where's from and what's it's fur
Mulan
@apollo5341
03/07/2025 - 11:16 AMLight follows a gradient of space-time density which is highest near massive celestial bodies such as the sun, a lesser space-time density than the Sun is Also near the near the Earth, with the greatest space-time density in the elements of the Earth itself, its gasses to the Earths heavy metals.
@TomHendricksMusea
03/07/2025 - 11:16 AMThe Curvature of Space May Be Caused by Anti Gravity, Not Gravity.
The curvature of space is now defined as this: Massive bodies, like planets, have gravitational fields around them that causes light or any matter to travel in curved paths around them.
My suggestion is that the expanding space caused by dark energy, an anti gravity like force, causes light or matter to travel in curved paths around massive bodies.
Therefore it's not gravity causing curved space, but the anti gravity force, dark energy causing curved space.
The expanding force of dark energy is 70% of the universe and by far the greatest force in the universe. It pushes and expands everywhere in space. But it is weakest where there is massive bodies; because, there is no empty space there to push back from!
The dark energy drops off significantly near massive bodies. This dark energy pushes or expands from all sides. But there is little dark energy pushing back between the planet and a passing photon, or matter of any kind. That's where dark energy is the weakest.
Therefore any photons or matter of any kind that is nearing a planet are pushed by dark energy toward the planet.
They are pushed toward it from empty space, not pulled toward it because of gravity.
The expanding force of dark energy between any planet and a photon is weak and weaker the closer the two objects are to each other. This is the opposite of gravity.
See drawing. When the photon traveling from left to right approaches the planet, dark energy striking the planet from all sides is much greater than the weak amount of dark energy between the photon and planet. This causes the photon to be pushed toward the planet in a curved path.
This helps explains an alternate reason for the curvature of space. This suggests curvature of space is caused by dark energy.
@SamsungGalaxy-vw9gy
03/07/2025 - 11:16 AMAre u a real professor?
@chandanpandey1862
03/07/2025 - 11:16 AMThe question is… How is that one large mass curving space-time in order to give other bodies a movement thereby creating a gravitational force? Rest everything is reacting to some really really large mass but what is that mass reacting to? How is that large mass curving anything?
@koyaaanisquatsi
03/07/2025 - 11:16 AMyou are speaking too fast, I had to slow it down to make sure I really understand (I don't study or work in physics)
@rossholst5315
03/07/2025 - 11:16 AMWe often say that gravitational lensing is dependent upon the presence of a massive object.
How does density affect the lensing? Could we have a very massive yet very voluminous object (a massive object with low density and large volume) cause the warping?
How about a plethora of small masses that sum to the total mass of a large object, spaced out such that constructive interference occurs between the spaced small mass objects?
I would think the density would affect the focal points.
@kokomanation
03/07/2025 - 11:16 AMWe don’t what kind of matter the spacetime fabric is made off because for it to exist it must have some physical properties
@a2t4r75
03/07/2025 - 11:16 AMIt’s 3am and I’m laying here in my bed watching videos about general relativity.
@thomasolson7447
03/07/2025 - 11:16 AMYou can merge them with the quadratic formula.
@Zhroomy
03/07/2025 - 11:16 AMSo I have a question, Prof. Dave: Would another analogy of how gravity interacts with the universe be to imagine a cavitation bubble under water, with the water being space/time and the cavitation bubble being matter/planets/stars? The ‘water’ wants to collapse onto the cavitation bubble and it doing that pulls in any surrounding ‘water’ and with it the items (matter/dust/planets/etc)? But the ‘water’ causes ‘cavitation bubbles’ of any kind of matter to pull in any other items. I have trouble imagining gravity using a sheet of fabric and metal balls, despite the concept being that the curvature of space time makes objects try to fall into the center of a source of gravity.
@moupiyasawoo1504
03/07/2025 - 11:16 AMWhenever I think about general relativity, the question comes to my mind is that if the planets are following the curvature created by the sun in the spacetime fabric, why the planets don't fall into the sun eventually?
@trwagner1
03/07/2025 - 11:16 AMWait, gravitational lensing is not as simple as you explain
@trwagner1
03/07/2025 - 11:16 AMAnd, how to gravity "propagate? 😉 just posing the question
@trwagner1
03/07/2025 - 11:16 AMSO, all this to enforce our understanding that the expending of energy, no matter the source, results in "waves"?
@trwagner1
03/07/2025 - 11:16 AMOften with science, there are exceptions. theories are that, not facts. Your information that our brains can't understand and that our brains can only understand 3 spatial dimensions, doesn't make sense, because you go on in an attempt to explain them.
@1014AH
03/07/2025 - 11:16 AMShady cloudy and image differs the Closer you get
@fadhilm.c.6420
03/07/2025 - 11:16 AMThis is probably the most simplified explaination of GR I’ve ever seen.
@hmmm1482
03/07/2025 - 11:16 AMi.e. except time there is one more dimension to the 3 we know? So if we count time as dimension too, then there are actually 5 dimensions??????
@WalterHildahl
03/07/2025 - 11:16 AMLight can follow a straight path thru curved spacetime.
@Karim-nq1be
03/07/2025 - 11:16 AMI don't get what it means for the space to be curved, I do get the idea of a manifold in maths but I don't get the physical idea of a curved space.
@intelligentdesign4435
03/07/2025 - 11:16 AMTHIS IS an stupid explanation. Oh my goodness..
@Hussain9077
03/07/2025 - 11:16 AMLight doesn’t follow a curved path, our perception of the path that it is curved, but maybe it is not curved, maybe the path exists in another dimension
@curlyhum1276
03/07/2025 - 11:16 AMlet me write what i got from this mini lecture Professor: gravity is like a magnet in that it has an attraction force within it, electromagnetic force travels through space in an ordered sign wave fashion with electric and magnetic system that shares this up and down motion that balances out the energy keeping it in a straight line . if we look at light in the form of a laser passing by a large space object like earth general relativity tells us that the gravity transmitted by the planet will bend the light do to its effect on the mass in the light?
so the mass of the planet effects the mass of the light causing it to look like its bending or curving around this gravity waves of earth? so the light no longer is following a straight path but a curved path do to gravity of the source effect body. so your saying the force of gravity of the planet can warp the light rays but not space time? i fail to make any connection between space curvature and the bending of light by a planet? space itself does not bed at tall? what is bending or to cause to appear as curving is the action of gravity acting on a light ray that has some number of mass do to the effect of gravity in play. therefore space time is constant around a planet but gravity does effect any mass within its proximity, outside this critical distance there is a net zero effect of gravity do to its distance from the core of the mass.
Gravity could only be some form as yet not identified within the electromatic spectrum like X-ray UV light and so on, gravity is a net effect of all mass within a three dimensional field that sums to a quantum number of gravity force that can act on any other mass be it light or particles. if you want to build a gravity weapon you need to create gravity by mining mass , extracting the gravity magnets particles that sum together causing gravity waves , once you gain a net unit of one gravity unit you can then use electricity to amp up the waves allowing one to use it as a tool to pull in objects or reverse polarity to repulse objects. push pull at the flip of a switch! the idea of space curving or bending is an incomplete childish description like the big bang theory or the theory of evolution in the face of a God creator. what appears like space bending is just the path of the lights travel , space its self does not bend for space lacks all mass and is just empty void volume that mass energy plays in!
@variousvideos5248
03/07/2025 - 11:16 AMnice from india
@uncle-epicurus
03/07/2025 - 11:16 AMI've always thought that the two dimensions of classical portrayals of black holes were incorrect. In reality I think the real thing is actually a "black sphere" & in 4D.
x, y, z, t.
@bienjifaylon7114
03/07/2025 - 11:16 AMWhat causes massive object press down spacetime? Just asking..
@jibinkjose1073
03/07/2025 - 11:16 AMGreat video. But one point to note: Massive objects bend/curve spacetime and not space itself. In other words,they accelerate space towards themselves.
@ahsanrubel2869
03/07/2025 - 11:16 AM3 spatial dimensions are curved around a 4th spatial dimension!? …. ?
@Black-mx3hc
03/07/2025 - 11:16 AMSo is the curved spacetime 3d? What is the 4th dimension then
@christianhill3244
03/07/2025 - 11:16 AMIsn't it like a fuzzy ball…the curvature of space
@liminal27
03/07/2025 - 11:16 AMH~O~W does matter curve spacetime. HOW…how does it do that. HOWWWWWWWW does it do it. I get that it DOES but HOWWWWWWWWW does it happen. HOW. Edit: If science doesn't know the answer to that question please just say, "science doesn't know the answer to that question (yet)."
@AB7524EVA
03/07/2025 - 11:16 AMIf space and time fill everywhere in the universe than why are we only focusing on the bottom side of a planet or mass. The same thing would apply at the top . Middle and bottom. After all the universe is not a sheet of paper or trampoline mat is it?
@hamzaayech5966
03/07/2025 - 11:16 AMThanks for this video! But i have one remark, i think you should tell people that the curvature caused by objects is not like the one that's visualized in your video, i understand that's a 2D representation, but i think if you used a 3d one it will make people understand more and more.
@CasualGlassEnjoyer
03/07/2025 - 11:16 AMExplains gravity. (Note to self)
@aeonsleo2
03/07/2025 - 11:16 AMSpacetime does not curve because bending is a three dimensional feature. We have to use some fourth dimension term.
@africanhistory
03/07/2025 - 11:16 AMI came confused and left more so— nice one.
@dimitristripakis7364
03/07/2025 - 11:16 AMCan someone explain why "mass curves spacetime" and not "mass curves space only" ?
I mean, an object that travels near the Sun turns towards it in space (so its "straight trajectory" becomes a curve), Ok fine.
But that is curving the space. What does time has to do with it ?
@wehrewulf
03/07/2025 - 11:16 AMQuantum Field Theory says there is no curvature of space, and that gravity is not a product of a mass's interaction with local space.