What is the difference between big "G" and little "g"... And what is gravitational lensing? More physics and astronomy at www.sixtysymbol... With Laurence Eaves, Mike Merrifield and Meghan Gray.
Back in Physics in high school I had my own equation/constants sheet as well, lol. It's pretty common for any Physicist worth his salt. Physics prefers you to memorize the concepts and how to manipulate things properly, not just wrote memorization of equations and constants. That's why even in college they let you have an equation/constants sheet, even on tests ;)
1:06 I'd like to show this to every one of my math/physics teachers who have claimed we have to remember every formula and every value by heart until an upcoming test.
Indeed but this applies more to non physics science. Biology, etc is overwhelming memorisation and often rote memorisation at that. It really annoyed Feynman who became a biologist for awhile.
It's the most common analogy to help visual how gravity informs/deforms the curvature of spacetime, how gravity can be thought as just that curvature itself. A trampoline is often replaced for the couch in many versions of the analogy. It's a great analogy as long as you understand the limits and context of said analogy.
If we only see the deflected images of objets behind other massive objects of which we don't originally know the mass, how is it possible to know from where the light came in the first place? I didn't get that from the fist explanation :S
I genuinely love your vids, Brady. You're doing a great service to science and us all. ps I thought the force of gravity didn't exist, it was just the deformation of space-time?
I was one of the citizen scientists on Spacewarps - looking through CFHTLS photos (Canada, France, Hawaii, Telescopic Lens Survey) Our goal was to I.D. new gravitational lenses. Having gone through a third of a million photos I can truthfully say that these lenses are one of the great wonders of the universe. Although they are but optical illusions they look real enough to touch. For non scientists and science geeks these citizen science projects are a unique blessing. You never know what the next slide will show. At times, you can be the first human to see a jaw-dropping wonder. You can liken it to the first person to lay eyes on the island of Oahu. This seems like a good spot to slip in a good word for these amazing projects that benefit everyone.
I love these videos. I'm not particularly mathematically inclined but these videos have helped bridge the gap in my mind between variables and constants in equations and natural phenomenon. I have a background in English rhetoric and composition, so when asked to describe the physical world I use parts of speech to do so, which can be arranged according to the rules of grammar. These videos are showing me that mathematics does the same thing, but instead of using words mathematicians use equations and constants.
p=mv is actually an approximation. The equation in special relativity is actually p= γmv where γ=1/sqrt(1-β^2) and m is the rest mass (mass when not moving since objects get more massive when moving). β = v/c so when you apply this equation to photons you get: p= 1/0 (0)c which is undefined. However if we use Einstein's equation E^2=m^2c^4+p^2c^2, which reduces to E=pc for a photon we get that the momentum of light is actually equal to its energy divided by its speed.
I said root 1-(v/c)2 will give you time dilation and length contraction, not that relativistic mass caused them. After reading the paper you cited the argument is about whether mass or momentum is the correct concept to use, with Einstein in favour of keeping the maths pure. This is an ongoing controversy, not a decided issue, but in light of it I happily amend my position. The explanation I gave was not an accurate description but a simplified analogy that can't be pushed too far.
Only wish is that some of them had discussed the experiment in which G was measured. I've never quite understood how Cavendish managed to account for all effects of earth's gravitational field. Like obviously in Y, but there's also compression in X too, which he couldn't have anticipated and I've never heard of anyone re-measuring the constant.
The scientist from 5:35 to 8:00 Basically explained 2 weeks of studying in my school and discussing the big G and the effect of gravity on other things... Big kudos to her, she's really great..
Good question, and I should have elabortaed. p = m v is the classical physics definition. In quantum physics it's p = (Planck constant h) / wavelength. You can combine both definitions to find the RELATIVISTIC mass m = h / (wavelength c), but that's not mass in the classical sense.
you can see the original object, the lens and the bent light. those 3 points allow you to make an angle. the distances of the source and the lens can be found through examining the red-shift of the light from each.
Physicists discuss G the gravitational constant, which is one of the most fundamental constants of physics (1 of 7.) In this video, the gravitational lenses is explained beautifully by a lady astrophysicist. Recommended.
Also, in the case of dark matter: we can actually see right through dark matter. If the light is coming directly at us it is going straight through the center of the lens and will not get distorted. In that case we have an image and the original. I looked up some images: the closer you get to the ring, the more distorted the image becomes, so that's another way to find where the ring would be.
The confusion with this principle is that we use newton and some mystery force to explain local effects and Einstein gravity is based on space time in the macro universal sense. So like he said we dont have a full theory on gravity or the gravaton so we kinda just say magical force that we only observe here lol. I'd love to know how we can square these opposing theories, and then how space time theory relates to the ball I throw in the air and atoms as well:) I've struggled alot with G so insight would be much appreciated:)
Actually that's pretty much one of the main problems in modern physics. Classical physics and Quantum physics can't agree on how gravity works. So currently they've just sort of drawn an arbitrary line in the sand and said "on this side we use classical gravity, on this side we use quantum gravity." If you could provide insight into that problem you'd probably win a Nobel Prize...lol
The concept of relative mass isn't outdated when considering why an object with rest mass can't be accelerated to light speed. E=mc2 holds at rest or in motion because the formula you gave above allows any extra kinetic energy to be accounted for in the equation. In fact it allows you to work out how much your mass increases, how much you would contract in the direction of travel and the amount of time dilation you would experience relative to an observer. So use the equations and then (cont'd)
I'm not sure your mirror analogy quite encompasses the phenomenon of gravitational lensing. Lenses refract light, mirrors reflect. However, it is possible to have two galaxies both appear to be in the same place (ignoring distance).... two galaxies in a row whose alignment coincides with the leading edge of the lensing mass relative to them. We would see a distorted double galaxy. The only other way, and I suspect is what you are envisioning, would involve too great a distance for size (cont)
Well, we know its x & y coordinates, because in order for us to be able to see it, it must be aligned with us and the deflecting mass (as stated in the video), so we just need to work out its distance from us, and this can be calculated (assuming it's sufficiently far away) by the red-shift of the light emitted from the object, allowing us to measure the angle.
My guess would be they can measure it because we are not dealing with a single point but a section of light being bended, thus the far sides (the one closest to the lensing source and the one farthest) will be bent at a different strength and analysis of the difference would allow you to derive the position of the original.
Remember, gravity is the curvature of spacetime. Since photons propagate directly through space, curving space is equivalent to curving the path of the photons. It's like drawing a line (representing the light) on a piece of paper (representing space) and then bending the paper (representing curvature due to gravity). You would notice that the line is now curved. Similarly, light traveling through curved spacetime appears curved.
@ispravljat Light is both a particle and a wave. Sometimes it behaves like the "stuff" in your microwave that makes things hot, sometimes it behaves like the grains of sand fired through a sandblaster. Gravity's effect on light falls in the behaviors associated with the latter. Far too much to fit in a CZcams comment, though our high school physics class learned all about it.
Brady, make the videos longer. Have them explain the things they mention. I mean, it's great that you told us that by measuring the angle between the real light source and the image we see of it we can calculate the mass of the deflecting object, but we don't know how you can measure that angle since it isn't known where the real object actually is.
Practically, gravity is to small too measure in quantum scale experiments, but also there is a theoretical issue. When considering the other forces that operate at human scales, then in QM, certain particles behave such that at our scale they resolve into these classical forces. But with gravity, it has to resolve into the bending of space-time, because we already know that at large sales, gravity is really a side effect of bent of space-time rather than a force. So this is uniquely different.
My guess is that they don't just use a single light source but look at multiple ones. That Einstein ring is a certain distance away from the center. A lot of images will be scattered on that ring because there are many light sources _almost_ perfectly behind it (because of the scale of the universe). The change from nothing inside the ring to more than usual in the ring should be fairly obvious, allowing you to reconstruct the ring and use that to calculate the angle. But I could be wrong...
@dudejohnny did you watch the video? The bit at the end talking about lensing? the mass of the star doing the lensing would dictate how far the light was bent. The mass of it has to be assumed, how ever gravity would shift the polorazation properties of the light and that you can measure dirrectly.
Actually, photons don't get frames of reference in special relativity. Trying to make sense out of them leads to nonsense, like the fact a photon would experience no time at all. We simply discriminate against massless particles that way, they don't get FoRs. Also, in general relativity, ANY object under a gravitational pull is really moving in a straight line, just through curved space. The earth is moving in a straight line through the curved space around the Sun. So, you're correct.
@puncheex Actually they only have to be in a straight line to get a complete Einstein ring. Usually they aren't in a straight line, so instead of a ring you see a curved distorted image. From what I've read since this video, I believe astronomers can measure the distortion and from that calculate the amount the light was bent. This has let them compute the density variations in a huge region of dark matter, which is much harder than analyzing a concentrated mass like a star or galaxy.
About gravitational lensing: So when the light is put on another path, it could actually look as if for example two galaxies are at the exact same position in space, because their images are overlapping?
because of e=mc2. The faster an object travels, the more energy it has in addition to the energy value of its mass. If e increases and c2 can't, then m must increase as a logical consequence of the equation. The more mass you have the more energy it takes to accelerate you, which in turn increases your mass further, until the energy required to accelerate you more becomes infinite. As for why, Einstein wrote a book explaining relativity in layman's terms, which would probably interest you
@BULLBRANDDAN It's actually just the light of the moon (which is the light of the sun) refracted through either ice crystals in the atmosphere, or moisture in the clouds, much like a rainbow after a rain shower.
I think it's amazing that Einstein and other scientists could predict stuff like the Einstein ring. He must have been incredibly smart... And he was...
E=Mc² is explicitly for rest mass only. Also relativistic mass is an old concept that has fallen almost completely out of favour, very few scientists still use the concept as it is just a poor way to try to make classical ideas (E.g. F=ma) still apply, and it obscures the actual physics and in many cases using it results in things that just aren't true. E.g. the use of relativistic mass would predict a fast moving up quark could decay into a top quark which can't happen.
So does this imply that the "coordinate system" of our universe is space vs time vs mass? So that all relativity becomes just a surface equation, and that gravity is a partial derivative of this surface equation?
That's the most understandable answer I've read so far. From the perspective of the photon, it's still travelling in a straight line? But when observed from a different location in space it appears to warp? (un-schooled thanks)
True! This is an invitation to see an artist theory on the physics of light and time! Based on just one equation (E= ˠ M˳C²) ∞ the Lorentz contraction of space and time is between the energy and mass. The greater the energy the greater the contraction of space and the slower time will run. Mass will increase relative to this and each ref-frame can be seen as a vortex in space formed by the rate that time flows. The brackets represent the boundary condition of the ref-frame within infinity!
Because it is assumed that the laws of physics are the same at any speed. Light speed is determined by two constants to do with electromagnetism, if the speed of light was different for you going at a high speed that would mean these 2 constants would be different for you at this speed and hence the laws of physics would not be the same. After going through some (relatively simple, nothing more than Pythagoras) maths assuming that speed of light must be constant at all speeds that limit arises.
This objects in space are constantly moving, and even we are moving, so this is not a static picture. So for example, we can look at the source of light even before its light has been bended, and then watch how light from the source distorted, like in a curved mirror.
", that they give conflicting results at the sub-atomic level isn't exactly news to anyone. " It entirely is. Quantum mechanics incorporates special relativity into it. Even Einstein said not to use the concept of relativistic mass as it is a bad concept that does nothing except cause inaccuracies. No it does not explain at all how much you would contract or how much time would dilate, the idea of relativistic mass is to cause the physics to work without having lorentz transformations.
a stretchy fabric. Imagine shoving a large ball into that springy matrix and all the tubes would bend out of the way and around the large ball, but that's not how the large ball distorts space. Instead of pushing the tubes out of the way, the distortion would appear as though the tubes were sucked into the center of the large ball, and that suckage would have less effect on the tubes the farther away they are from the large ball. That's how I imagine it.
Love the channel and the related channels Brady, great stuff. But please what is up with British CZcams channels having their audio normalized so low? Yeesh.
@qkn30989 Yes, I suppose you could. The distance it would have to travel to actually double back around to it's source would be phenomenal though, given that we can just barely see (often not with visible light) massive planets orbiting other relatively close stars that would pretty much make it useless. There is also the problem that the light would become distorted as it bent around so many sources of gravity, and the natural dispersal of the light eventually completely nullifying the image.
At one point you say, (around 1:10) that you have a calculator with the constants built in.. Can you tell me what the calculator is, make/model or anything, an/or where to get one. THANKS GUYS KEEP UP THE VIDEOS !!
I realize what it looks like, I was just guessing around: Imagine a half reflecting mirror (half the light goes through, the other half is reflected) and you put a light source behind the mirror and in a 45° angle to the mirror at the same distance from the mirror, they'd basically look like they were a single light source from a observer positioned in a 45° angle to the mirror. (like this: Light source on the ground, mirror in 45° angle and lightsource behind mirror)
I read somewhere that Galileo never actually dropped anything from the Tower of Pisa! Instead, he looked at how different sized balls of different materials rolled down a slope and from there he deduced that gravity acted upon everything equally.
isn't about the one system?... i mean when u put the butter on a toast they will become one system and before falling down to the floor, they will have to be stable, so before even falling down it will turn upsidedown.. i mean let's attach the butter to a string and then put the butter on one side, so it will have to rotate on that string butter side down... because of the mass and (f=ma).. that's why we use the balance... it will turn in the heavy side first i donno :), would you tell me why?
@soppybollocks11880 gravity as described by the video can even warp space, which is a vacuum (light travels at different speeds at different atmospheres we only get the constant when it is in a vacuum), so why can it not warp light? thus in layman's terms gravity > vacuum > light
But if the original is hidden behind something and all you are seeing is the lensed image of the original, then how do you know where the original is? Is there a way of knowing?
The mass of an object causes a curvature of space/time, hence light travels in a straight line though space/time, but space time is curved giving the appearance of light deflection.
For years this has bothered me, and I don't know where else to ask: If fermions are effectively embedded in spacetime, then it seems that distortions would directly affect them without the need for any intermediary. I don't understand where gravitons come from, as in, why theories require them to be a separate entity like the strong, weak, and electromagnetic force, rather than gravity being an innate feature of spacetime.
no, a black hole can capture light because photons actually are matter, however, gravitrons are more points of time and space that have been bent to attract matter to a large mass, like points on a sheet with a weight in the middle. in actuality, gravity is what powers a black hole. beyond the event horizon nothing with mass can escape.
Yes I am confused, because this demo doesn't help in explaining gravity. Without gravity, this demo would not work. The ball would continue in the same direction, as the dimpled cushion dropped out from underneath it. If you're saying the ball would continue to travel in a straight line, but that line is distorted by gravity, this demo still doesn't work for that. I think a better visual demo would be a matrix of tubes in which the ball would travel. Those tubes are attached by springs, making
@soppybollocks11880 There is no distinction between mass and energy in the light of general relativity. They are just the same thing appearing different from different frames of reference.
Wait - you said the gravitational effects are instantaneous. How is that possible? If it is a particle ("gravitron" is used in this movie) - nothing travels faster than light (as far as we know). I guess it comes down to: what is gravity????
At 4:32 you say "the average density of mars and earth are about the same." In fact mars is 28.6% less dense to be precise. That's not "about the same." Other than that ...I liked your video.
Because it has momentum, and that's affected too. The famous E=m c^2 is not the full picture. If it were then a photon wouldn't have no energy, since m = 0, and of course that's nonsense. That part is only valid for matter which has mass and is at rest. The full equation is E^2 = (m c^2)^2 + (p c)^2 where p is momentum. May look daunting, but upon closer observation it looks like Pythagoras' equation a^2 + b^2 = c^2. The factor a here is the familiar m c^2.
(cont) apparent sizes to line up. The only I can think of to get one lensed galaxy in the same apparent position is for the unlensed galaxy to be in front of the lensing mass which projects the image of an even further galaxy. We would see a huge galaxy (closest to us) with a tiny little lensed galaxy inside (behind) it. The disparity in distance would render our observation as unremarkable and obvious. In case that's not quite the scenario you had in mind...I'll go a step further for ya (cont)
point out to me why my original comment (to someone other than you) was inaccurate in explaining why you can't accelerate something with rest mass to the speed of light? As for the decay of quarks, you would explain them using quantum physics not relativity, that they give conflicting results at the sub-atomic level isn't exactly news to anyone.
Does this mean that every object in space is not where we see it to be because of the existence of gravity between us and the object? Does that mean that if a galaxy that is thousands of light years away, which we see at position X, is actually at a different location (Y) because the light that has been emitted from the galaxy has been directed, by forces of gravity, to eventually arrive at our planet?
Bhuvan Kandel if you look into Albert Einstein’s experiment on gravitational lending you will understand better. They plotted the position of stars and tried to measure how much the light from those stars was manipulated when our sun was between us and the stars, but in order to see they had to do this during a total eclipse and low and behold the stars appeared to alter position, due to our sun “bending” the light due to gravity.
actually the couch doesnt warp instantly ...the couch warps at a finite speed .. in slow motion u would see the fabric shuddering like a "wave" ....like when u throw a ball against a glass window , in slow motion the window "warps" like a wave .. thats how space works ...but faster ..at the speed of light , gravitational waves move at "c"
So if we cant tell where the source light is coming from after it has been deflected from an object, how can we measure the angle of where we actually see it?
@appelelle The third time she called the attention on her fist I felt a little intimidated (my little g actually) *chills*. Jokes apart, this whole series is awesome!
Think of two people who set off at right angles from the south pole, if they don't know their on a sphere they would see there initial right angle velocity being deflecting towards each other until they collide at the north pole, they could explain that by saying there is some force that pulled them towards each other. Thats wort of how gravity works, but it works with space and time and so the vertical motion in my example could be moving through time instead of space.
Could you help translate? I'm not quite that advanced. What I got was: That would be like a vacuum, it sucks strongly, that it * the suction away and * * sucks... ?
According to current theory, mass warps 'space'. We can see this due to what we perceive to be gravitational lensing. That's 'if' our perceptions and theories of gravity prove to be true. If so, can it be considered that 'space' has become more 'dense' moving toward the center of mass in the presents of that mass or more 'rarefied'? I'm not so sure that that is even a viable question? Thank you.
Gravity is the only force we can’t combined with the other. We want relatively to be fully compatible with quantum mechanics. So we want quantum gravity (gravitons) to fit in a nice theory of everything. May not turn out that way but that’s the idea.
From Professor Merrifield.... "Why would a scientist eliminate a book from his shelf just because he doesnt believe what it says. If you want to argue against creationism, it is probably a good idea to find out what it claims."
@sixtysymbols If Fg=(Gm₁m₂)/(r²) what would be the the force of gravity be like between a massive object and a cluster dark matter with centers of gravity at the same point?
In classical physics, G is simply a constant from which you can determine how much force 2 masses exert upon one another through gravity. Basically if you have m0 and m1 (2 masses), the force that attracts each other through gravitation is m0.m1.G/d^2 (where d^2 is the distance between the center of mass of the 2 object squared). This constant was postulated by Newton and first determined (with pretty good precision) by Cavendish. It is important because it is one of the 3 basic constants of the universe (the others 2 being the Planck constant and c, the speed of light).. (On a sidenote : I kind of remember Epsilon0 - the electrical permessivity of vacuum also being one - but it can possibly be infered by the other 3 constants).
Ivan Warren That is not quite correct. For once, there are 26 fundamental constants to the universe, as we know it today, and none of them can be inferred by the other ones (otherwise it would not be fundamental).As for the vacuum permittivity: it can be calculated from e, the elementary charge, h the Planck constant and c the speed of light in vacuum. As such it si not considered a fundamental constant.If you disagree, I would like you to derive e.g. the mass of the top-quark from your three "basic constants".
@danielbluesmoke Yes, but if the photon has taught us anything it's that sometimes things have duality. Photons can act as both waves and particles. Electrons too. We should keep am open mind to the graviton.
I still dont get the fist on the couch - gravity warping space - analogy. Her fist warps the couch instantly - but warping space/time occurs at a finite speed (c I think). Isn't there a better analogy?? Also like the ball - the light would speed up as it nears the object. This seems to be impossible.
Well, no. First of all, gravitons haven't been discovered yet, that's one of the reasons why physicists haven't been able to link General Relativity with Quantum Mechanics yet. The way gravitation works is, it bends space and time. Like the lady said in the video, it's kind of like a bowling ball on a trampoline. That indentation in the space time fabric is the reason behind the gravitational force.
@Entrepreneur101 I can understand how someone who does not have a degree in physics would not understand the first two, but the third one puzzles me. It takes a deep and severe lack of knowledge of classical mechanics to think that last one is a lie.
You've been thumbed down but I've given you one back up - I know what you mean. Not only is she attractive physically, but there's that brain, that awesome brain just lurking in there, waiting to be tapped over dinner. Again, hats off to the older professer, amazing chap. Very interesting talk, perticually as I came from a TED talk on Dark Matter which mentioned Einstein Rings.
@shagster1970 It's possible. However, the Standard Model has predicted the graviton (which, although I am not sure, might also be the Higgs boson), and all its previously predicted particles have been found. A theory's predictive power gives credence to its validity.
it does occur, i'm not sure when the next time this will be observable is, i remember seeing a simple, large home telescope with a distant image of Jupiter, as it passed near the view of a star, and right before it contacted (visually) the star, the star apeared to move. Videos of this with the sun are on youtube durring an eclipse when u can see the relativly dim stars behind the sun.
Does that work in some way with the clouds and the moon? Twice I have seen a perfect circle of cloud with the moon in the centre and it couldn't have been random, how could it have been perfect from where I was standing. The only problem is that the clouds are in front of the moon.
light can be bent by gravity, so at a certain distance from a black hole, the event horizon, you would be able to look to the side and see the back of your own head. the telescope bit is only because the light still has to travel very far, so it'd still appear to be many miles away
I've never understood the need for a graviton. If a mass bends space-time in an expanding universe (in higher-than-3D geometry), and gravity is a result of that geometry (Einstein's general), then shouldn't we be looking for the interaction that binds all particles to the "fabric" of space-time? Universal acceleration and this "binding" force is all that we'd need to produce the effect of gravity - in lieu of a mediator that "communicates" gravity between two objects. It seems that this interaction would be present even if no significant gravity presents itself between two small or distant objects, because it's really an interaction with space-time itself.
I love how the guy can just casually break out a card of physical constants in conversation.
Its called being gangster
Just went to Nottingham University's open day and the physics department gave me one for free.
Back in Physics in high school I had my own equation/constants sheet as well, lol. It's pretty common for any Physicist worth his salt. Physics prefers you to memorize the concepts and how to manipulate things properly, not just wrote memorization of equations and constants. That's why even in college they let you have an equation/constants sheet, even on tests ;)
0:34 He busts out the fundamental constants card from his wallet. That was awesome.
1:06 I'd like to show this to every one of my math/physics teachers who have claimed we have to remember every formula and every value by heart until an upcoming test.
... except professors don't set tests.
what?
You are not required to memorize constants, but constants and formulae are not the same.
timewasteland This is what they do in high schools for the students who are better at remembering than actually solving physics problems.
Indeed but this applies more to non physics science. Biology, etc is overwhelming memorisation and often rote memorisation at that. It really annoyed Feynman who became a biologist for awhile.
That couch metaphor is the most simple easiest to understand explanation of gravitational lensing I've ever heard well done
+Joshua Lansell-Kenny Watch the video "gravity visualized". Saw it there the first time and it is a very cool video indeed.
its a pretty common way to explain gravity tho. If you watch some more lectures on gravity, u'll see lecturers use this demonstration very often.
It's the most common analogy to help visual how gravity informs/deforms the curvature of spacetime, how gravity can be thought as just that curvature itself. A trampoline is often replaced for the couch in many versions of the analogy. It's a great analogy as long as you understand the limits and context of said analogy.
Could you do a video on the Einstein field equations?
these physicists are proper inspiration! dont ever stop making these videos.
makes mne want to to go to uni of nottingham.
big G sounds like rapper
and little G
Lil' g is his son
That's because it is. A wrapper.
Ok
Cool. The "couch" analogy was really informative. Made a lot more sense than a lot of other YT videos I've seen on the topic!
If we only see the deflected images of objets behind other massive objects of which we don't originally know the mass, how is it possible to know from where the light came in the first place? I didn't get that from the fist explanation :S
I genuinely love your vids, Brady. You're doing a great service to science and us all.
ps I thought the force of gravity didn't exist, it was just the deformation of space-time?
In classical mechanics it can thought of like that but indeed we know it is due to the space-time curvature.
I was one of the citizen scientists on Spacewarps - looking through CFHTLS photos (Canada, France, Hawaii, Telescopic Lens Survey) Our goal was to I.D. new gravitational lenses. Having gone through a third of a million photos I can truthfully say that these lenses are one of the great wonders of the universe. Although they are but optical illusions they look real enough to touch. For non scientists and science geeks these citizen science projects are a unique blessing. You never know what the next slide will show. At times, you can be the first human to see a jaw-dropping wonder. You can liken it to the first person to lay eyes on the island of Oahu. This seems like a good spot to slip in a good word for these amazing projects that benefit everyone.
How did you get to do this?
Physicists just 'doodle' around with huge scary numbers all day and think about things.
Best most awesome job ever.
I love these videos. I'm not particularly mathematically inclined but these videos have helped bridge the gap in my mind between variables and constants in equations and natural phenomenon. I have a background in English rhetoric and composition, so when asked to describe the physical world I use parts of speech to do so, which can be arranged according to the rules of grammar. These videos are showing me that mathematics does the same thing, but instead of using words mathematicians use equations and constants.
Awesome video, especially there at the end.
p=mv is actually an approximation. The equation in special relativity is actually p= γmv where γ=1/sqrt(1-β^2) and m is the rest mass (mass when not moving since objects get more massive when moving). β = v/c so when you apply this equation to photons you get:
p= 1/0 (0)c which is undefined.
However if we use Einstein's equation E^2=m^2c^4+p^2c^2, which reduces to E=pc for a photon we get that the momentum of light is actually equal to its energy divided by its speed.
I said root 1-(v/c)2 will give you time dilation and length contraction, not that relativistic mass caused them. After reading the paper you cited the argument is about whether mass or momentum is the correct concept to use, with Einstein in favour of keeping the maths pure. This is an ongoing controversy, not a decided issue, but in light of it I happily amend my position. The explanation I gave was not an accurate description but a simplified analogy that can't be pushed too far.
Wow, that analogy of the woman (Brady, you never introduced her... as far as I know) really amazed me. Thanks for this great explanation.
Only wish is that some of them had discussed the experiment in which G was measured. I've never quite understood how Cavendish managed to account for all effects of earth's gravitational field. Like obviously in Y, but there's also compression in X too, which he couldn't have anticipated and I've never heard of anyone re-measuring the constant.
I love these videos guys, very well explained, even someone with a Finance degree can understand and appreciate !!
The scientist from 5:35 to 8:00 Basically explained 2 weeks of studying in my school and discussing the big G and the effect of gravity on other things...
Big kudos to her, she's really great..
Good question, and I should have elabortaed. p = m v is the classical physics definition. In quantum physics it's p = (Planck constant h) / wavelength. You can combine both definitions to find the RELATIVISTIC mass m = h / (wavelength c), but that's not mass in the classical sense.
you can see the original object, the lens and the bent light. those 3 points allow you to make an angle. the distances of the source and the lens can be found through examining the red-shift of the light from each.
I personally am astounded at the analogy of gravitational lensing, proposed by the woman. WOW.
Physicists discuss G the gravitational constant, which is one of the most fundamental constants of physics (1 of 7.) In this video, the gravitational lenses is explained beautifully by a lady astrophysicist. Recommended.
Also, in the case of dark matter: we can actually see right through dark matter. If the light is coming directly at us it is going straight through the center of the lens and will not get distorted. In that case we have an image and the original.
I looked up some images: the closer you get to the ring, the more distorted the image becomes, so that's another way to find where the ring would be.
The confusion with this principle is that we use newton and some mystery force to explain local effects and Einstein gravity is based on space time in the macro universal sense. So like he said we dont have a full theory on gravity or the gravaton so we kinda just say magical force that we only observe here lol. I'd love to know how we can square these opposing theories, and then how space time theory relates to the ball I throw in the air and atoms as well:) I've struggled alot with G so insight would be much appreciated:)
Actually that's pretty much one of the main problems in modern physics. Classical physics and Quantum physics can't agree on how gravity works. So currently they've just sort of drawn an arbitrary line in the sand and said "on this side we use classical gravity, on this side we use quantum gravity." If you could provide insight into that problem you'd probably win a Nobel Prize...lol
Kirhean They don't draw a line in the sand between them, they just don't have a proper quantum gravity theory.
The concept of relative mass isn't outdated when considering why an object with rest mass can't be accelerated to light speed. E=mc2 holds at rest or in motion because the formula you gave above allows any extra kinetic energy to be accounted for in the equation. In fact it allows you to work out how much your mass increases, how much you would contract in the direction of travel and the amount of time dilation you would experience relative to an observer. So use the equations and then (cont'd)
I'm not sure your mirror analogy quite encompasses the phenomenon of gravitational lensing. Lenses refract light, mirrors reflect. However, it is possible to have two galaxies both appear to be in the same place (ignoring distance).... two galaxies in a row whose alignment coincides with the leading edge of the lensing mass relative to them. We would see a distorted double galaxy. The only other way, and I suspect is what you are envisioning, would involve too great a distance for size (cont)
Well, we know its x & y coordinates, because in order for us to be able to see it, it must be aligned with us and the deflecting mass (as stated in the video), so we just need to work out its distance from us, and this can be calculated (assuming it's sufficiently far away) by the red-shift of the light emitted from the object, allowing us to measure the angle.
My guess would be they can measure it because we are not dealing with a single point but a section of light being bended, thus the far sides (the one closest to the lensing source and the one farthest) will be bent at a different strength and analysis of the difference would allow you to derive the position of the original.
subscribing Sixty Simbols is one of the best things i ever done :D
Remember, gravity is the curvature of spacetime. Since photons propagate directly through space, curving space is equivalent to curving the path of the photons. It's like drawing a line (representing the light) on a piece of paper (representing space) and then bending the paper (representing curvature due to gravity). You would notice that the line is now curved. Similarly, light traveling through curved spacetime appears curved.
@ispravljat Light is both a particle and a wave. Sometimes it behaves like the "stuff" in your microwave that makes things hot, sometimes it behaves like the grains of sand fired through a sandblaster. Gravity's effect on light falls in the behaviors associated with the latter. Far too much to fit in a CZcams comment, though our high school physics class learned all about it.
Brady, make the videos longer. Have them explain the things they mention. I mean, it's great that you told us that by measuring the angle between the real light source and the image we see of it we can calculate the mass of the deflecting object, but we don't know how you can measure that angle since it isn't known where the real object actually is.
Practically, gravity is to small too measure in quantum scale experiments, but also there is a theoretical issue. When considering the other forces that operate at human scales, then in QM, certain particles behave such that at our scale they resolve into these classical forces. But with gravity, it has to resolve into the bending of space-time, because we already know that at large sales, gravity is really a side effect of bent of space-time rather than a force. So this is uniquely different.
Love this channel so. Old by todays standards but humble and embodied. Still make people watch it from time to time :)
My guess is that they don't just use a single light source but look at multiple ones. That Einstein ring is a certain distance away from the center. A lot of images will be scattered on that ring because there are many light sources _almost_ perfectly behind it (because of the scale of the universe). The change from nothing inside the ring to more than usual in the ring should be fairly obvious, allowing you to reconstruct the ring and use that to calculate the angle.
But I could be wrong...
@dudejohnny did you watch the video? The bit at the end talking about lensing? the mass of the star doing the lensing would dictate how far the light was bent. The mass of it has to be assumed, how ever gravity would shift the polorazation properties of the light and that you can measure dirrectly.
Actually, photons don't get frames of reference in special relativity. Trying to make sense out of them leads to nonsense, like the fact a photon would experience no time at all. We simply discriminate against massless particles that way, they don't get FoRs.
Also, in general relativity, ANY object under a gravitational pull is really moving in a straight line, just through curved space. The earth is moving in a straight line through the curved space around the Sun. So, you're correct.
@puncheex Actually they only have to be in a straight line to get a complete Einstein ring. Usually they aren't in a straight line, so instead of a ring you see a curved distorted image. From what I've read since this video, I believe astronomers can measure the distortion and from that calculate the amount the light was bent. This has let them compute the density variations in a huge region of dark matter, which is much harder than analyzing a concentrated mass like a star or galaxy.
About gravitational lensing: So when the light is put on another path, it could actually look as if for example two galaxies are at the exact same position in space, because their images are overlapping?
because of e=mc2. The faster an object travels, the more energy it has in addition to the energy value of its mass. If e increases and c2 can't, then m must increase as a logical consequence of the equation. The more mass you have the more energy it takes to accelerate you, which in turn increases your mass further, until the energy required to accelerate you more becomes infinite. As for why, Einstein wrote a book explaining relativity in layman's terms, which would probably interest you
@BULLBRANDDAN It's actually just the light of the moon (which is the light of the sun) refracted through either ice crystals in the atmosphere, or moisture in the clouds, much like a rainbow after a rain shower.
I think it's amazing that Einstein and other scientists could predict stuff like the Einstein ring. He must have been incredibly smart... And he was...
E=Mc² is explicitly for rest mass only. Also relativistic mass is an old concept that has fallen almost completely out of favour, very few scientists still use the concept as it is just a poor way to try to make classical ideas (E.g. F=ma) still apply, and it obscures the actual physics and in many cases using it results in things that just aren't true. E.g. the use of relativistic mass would predict a fast moving up quark could decay into a top quark which can't happen.
Best explanation of gravitational lensing that I've seen.
So does this imply that the "coordinate system" of our universe is space vs time vs mass? So that all relativity becomes just a surface equation, and that gravity is a partial derivative of this surface equation?
That's the most understandable answer I've read so far. From the perspective of the photon, it's still travelling in a straight line? But when observed from a different location in space it appears to warp? (un-schooled thanks)
True!
This is an invitation to see an artist theory on the physics of light and time! Based on just one equation (E= ˠ M˳C²) ∞ the Lorentz contraction of space and time is between the energy and mass. The greater the energy the greater the contraction of space and the slower time will run. Mass will increase relative to this and each ref-frame can be seen as a vortex in space formed by the rate that time flows. The brackets represent the boundary condition of the ref-frame within infinity!
Because it is assumed that the laws of physics are the same at any speed. Light speed is determined by two constants to do with electromagnetism, if the speed of light was different for you going at a high speed that would mean these 2 constants would be different for you at this speed and hence the laws of physics would not be the same.
After going through some (relatively simple, nothing more than Pythagoras) maths assuming that speed of light must be constant at all speeds that limit arises.
This objects in space are constantly moving, and even we are moving, so this is not a static picture.
So for example, we can look at the source of light even before its light has been bended, and then watch how light from the source distorted, like in a curved mirror.
", that they give conflicting results at the sub-atomic level isn't exactly news to anyone.
"
It entirely is. Quantum mechanics incorporates special relativity into it.
Even Einstein said not to use the concept of relativistic mass as it is a bad concept that does nothing except cause inaccuracies. No it does not explain at all how much you would contract or how much time would dilate, the idea of relativistic mass is to cause the physics to work without having lorentz transformations.
a stretchy fabric. Imagine shoving a large ball into that springy matrix and all the tubes would bend out of the way and around the large ball, but that's not how the large ball distorts space. Instead of pushing the tubes out of the way, the distortion would appear as though the tubes were sucked into the center of the large ball, and that suckage would have less effect on the tubes the farther away they are from the large ball. That's how I imagine it.
Love the channel and the related channels Brady, great stuff. But please what is up with British CZcams channels having their audio normalized so low? Yeesh.
@qkn30989 Yes, I suppose you could. The distance it would have to travel to actually double back around to it's source would be phenomenal though, given that we can just barely see (often not with visible light) massive planets orbiting other relatively close stars that would pretty much make it useless.
There is also the problem that the light would become distorted as it bent around so many sources of gravity, and the natural dispersal of the light eventually completely nullifying the image.
At one point you say, (around 1:10) that you have a calculator with the constants built in..
Can you tell me what the calculator is, make/model or anything, an/or where to get one.
THANKS GUYS KEEP UP THE VIDEOS !!
I realize what it looks like, I was just guessing around: Imagine a half reflecting mirror (half the light goes through, the other half is reflected) and you put a light source behind the mirror and in a 45° angle to the mirror at the same distance from the mirror, they'd basically look like they were a single light source from a observer positioned in a 45° angle to the mirror. (like this: Light source on the ground, mirror in 45° angle and lightsource behind mirror)
I read somewhere that Galileo never actually dropped anything from the Tower of Pisa! Instead, he looked at how different sized balls of different materials rolled down a slope and from there he deduced that gravity acted upon everything equally.
isn't about the one system?... i mean when u put the butter on a toast they will become one system and before falling down to the floor, they will have to be stable, so before even falling down it will turn upsidedown.. i mean let's attach the butter to a string and then put the butter on one side, so it will have to rotate on that string butter side down... because of the mass and (f=ma).. that's why we use the balance... it will turn in the heavy side first i donno :), would you tell me why?
@soppybollocks11880 gravity as described by the video can even warp space, which is a vacuum (light travels at different speeds at different atmospheres we only get the constant when it is in a vacuum), so why can it not warp light?
thus in layman's terms
gravity > vacuum > light
But if the original is hidden behind something and all you are seeing is the lensed image of the original, then how do you know where the original is? Is there a way of knowing?
The mass of an object causes a curvature of space/time, hence light travels in a straight line though space/time, but space time is curved giving the appearance of light deflection.
For years this has bothered me, and I don't know where else to ask: If fermions are effectively embedded in spacetime, then it seems that distortions would directly affect them without the need for any intermediary. I don't understand where gravitons come from, as in, why theories require them to be a separate entity like the strong, weak, and electromagnetic force, rather than gravity being an innate feature of spacetime.
no, a black hole can capture light because photons actually are matter, however, gravitrons are more points of time and space that have been bent to attract matter to a large mass, like points on a sheet with a weight in the middle. in actuality, gravity is what powers a black hole. beyond the event horizon nothing with mass can escape.
@qkn30989 NO. Light doesn`t orbit a center of mass, a material object does.
Yes I am confused, because this demo doesn't help in explaining gravity. Without gravity, this demo would not work. The ball would continue in the same direction, as the dimpled cushion dropped out from underneath it. If you're saying the ball would continue to travel in a straight line, but that line is distorted by gravity, this demo still doesn't work for that. I think a better visual demo would be a matrix of tubes in which the ball would travel. Those tubes are attached by springs, making
@soppybollocks11880 There is no distinction between mass and energy in the light of general relativity. They are just the same thing appearing different from different frames of reference.
Wait - you said the gravitational effects are instantaneous. How is that possible? If it is a particle ("gravitron" is used in this movie) - nothing travels faster than light (as far as we know). I guess it comes down to: what is gravity????
At 4:32 you say "the average density of mars and earth are about the same." In fact mars is 28.6% less dense to be precise. That's not "about the same."
Other than that ...I liked your video.
Because it has momentum, and that's affected too.
The famous E=m c^2 is not the full picture. If it were then a photon wouldn't have no energy, since m = 0, and of course that's nonsense. That part is only valid for matter which has mass and is at rest. The full equation is
E^2 = (m c^2)^2 + (p c)^2
where p is momentum. May look daunting, but upon closer observation it looks like Pythagoras' equation a^2 + b^2 = c^2. The factor a here is the familiar m c^2.
(cont) apparent sizes to line up. The only I can think of to get one lensed galaxy in the same apparent position is for the unlensed galaxy to be in front of the lensing mass which projects the image of an even further galaxy. We would see a huge galaxy (closest to us) with a tiny little lensed galaxy inside (behind) it. The disparity in distance would render our observation as unremarkable and obvious. In case that's not quite the scenario you had in mind...I'll go a step further for ya (cont)
point out to me why my original comment (to someone other than you) was inaccurate in explaining why you can't accelerate something with rest mass to the speed of light? As for the decay of quarks, you would explain them using quantum physics not relativity, that they give conflicting results at the sub-atomic level isn't exactly news to anyone.
@Erick Hernandez I think that cosmic speed limit of light still apply to gravitons.
Does this mean that every object in space is not where we see it to be because of the existence of gravity between us and the object? Does that mean that if a galaxy that is thousands of light years away, which we see at position X, is actually at a different location (Y) because the light that has been emitted from the galaxy has been directed, by forces of gravity, to eventually arrive at our planet?
Bhuvan Kandel if you look into Albert Einstein’s experiment on gravitational lending you will understand better. They plotted the position of stars and tried to measure how much the light from those stars was manipulated when our sun was between us and the stars, but in order to see they had to do this during a total eclipse and low and behold the stars appeared to alter position, due to our sun “bending” the light due to gravity.
actually the couch doesnt warp instantly ...the couch warps at a finite speed ..
in slow motion u would see the fabric shuddering like a "wave" ....like when u throw a ball against a glass window , in slow motion the window "warps" like a wave ..
thats how space works ...but faster ..at the speed of light , gravitational waves move at "c"
So if we cant tell where the source light is coming from after it has been deflected from an object, how can we measure the angle of where we actually see it?
@appelelle The third time she called the attention on her fist I felt a little intimidated (my little g actually) *chills*.
Jokes apart, this whole series is awesome!
How do you calculate the deflection angle if you don't know where the object originally was?
Think of two people who set off at right angles from the south pole, if they don't know their on a sphere they would see there initial right angle velocity being deflecting towards each other until they collide at the north pole, they could explain that by saying there is some force that pulled them towards each other. Thats wort of how gravity works, but it works with space and time and so the vertical motion in my example could be moving through time instead of space.
It's interesting that G constant is not a constant at all. There is a good TEDtalks about it.
Could you help translate? I'm not quite that advanced. What I got was: That would be like a vacuum, it sucks strongly, that it * the suction away and * * sucks... ?
According to current theory, mass warps 'space'. We can see this due to what we perceive to be gravitational lensing. That's 'if' our perceptions and theories of gravity prove to be true. If so, can it be considered that 'space' has become more 'dense' moving toward the center of mass in the presents of that mass or more 'rarefied'? I'm not so sure that that is even a viable question? Thank you.
Gravity is the only force we can’t combined with the other. We want relatively to be fully compatible with quantum mechanics. So we want quantum gravity (gravitons) to fit in a nice theory of everything. May not turn out that way but that’s the idea.
I think it's OK as long as it's presented as an analogy to gravity and not as a demonstration of gravity.
From Professor Merrifield.... "Why would a scientist eliminate a book from his shelf just because he doesnt believe what it says. If you want to argue against creationism, it is probably a good idea to find out what it claims."
@sixtysymbols If Fg=(Gm₁m₂)/(r²) what would be the the force of gravity be like between a massive object and a cluster dark matter with centers of gravity at the same point?
In classical physics, G is simply a constant from which you can determine how much force 2 masses exert upon one another through gravity. Basically if you have m0 and m1 (2 masses), the force that attracts each other through gravitation is m0.m1.G/d^2 (where d^2 is the distance between the center of mass of the 2 object squared). This constant was postulated by Newton and first determined (with pretty good precision) by Cavendish. It is important because it is one of the 3 basic constants of the universe (the others 2 being the Planck constant and c, the speed of light).. (On a sidenote : I kind of remember Epsilon0 - the electrical permessivity of vacuum also being one - but it can possibly be infered by the other 3 constants).
Ivan Warren That is not quite correct. For once, there are 26 fundamental constants to the universe, as we know it today, and none of them can be inferred by the other ones (otherwise it would not be fundamental).As for the vacuum permittivity: it can be calculated from e, the elementary charge, h the Planck constant and c the speed of light in vacuum. As such it si not considered a fundamental constant.If you disagree, I would like you to derive e.g. the mass of the top-quark from your three "basic constants".
Actually G was first determined by the Schiehallion experiment (on a mountain) with Charles Hutton and others.
@danielbluesmoke Yes, but if the photon has taught us anything it's that sometimes things have duality. Photons can act as both waves and particles. Electrons too. We should keep am open mind to the graviton.
I still dont get the fist on the couch - gravity warping space - analogy. Her fist warps the couch instantly - but warping space/time occurs at a finite speed (c I think). Isn't there a better analogy?? Also like the ball - the light would speed up as it nears the object. This seems to be impossible.
Well, no. First of all, gravitons haven't been discovered yet, that's one of the reasons why physicists haven't been able to link General Relativity with Quantum Mechanics yet.
The way gravitation works is, it bends space and time. Like the lady said in the video, it's kind of like a bowling ball on a trampoline. That indentation in the space time fabric is the reason behind the gravitational force.
@Entrepreneur101 I can understand how someone who does not have a degree in physics would not understand the first two, but the third one puzzles me. It takes a deep and severe lack of knowledge of classical mechanics to think that last one is a lie.
How do you put these values into your calculator? I have a graphical Casio and I have no idea how to do it...
how can you tell how far it has been rotated, by how much light is polorized in particular directions?
You've been thumbed down but I've given you one back up - I know what you mean.
Not only is she attractive physically, but there's that brain, that awesome brain just lurking in there, waiting to be tapped over dinner.
Again, hats off to the older professer, amazing chap. Very interesting talk, perticually as I came from a TED talk on Dark Matter which mentioned Einstein Rings.
Where do I find one of those cards?
Rangifulla i think he wrote it out
@shagster1970 It's possible. However, the Standard Model has predicted the graviton (which, although I am not sure, might also be the Higgs boson), and all its previously predicted particles have been found. A theory's predictive power gives credence to its validity.
it does occur, i'm not sure when the next time this will be observable is, i remember seeing a simple, large home telescope with a distant image of Jupiter, as it passed near the view of a star, and right before it contacted (visually) the star, the star apeared to move. Videos of this with the sun are on youtube durring an eclipse when u can see the relativly dim stars behind the sun.
Does that work in some way with the clouds and the moon? Twice I have seen a perfect circle of cloud with the moon in the centre and it couldn't have been random, how could it have been perfect from where I was standing. The only problem is that the clouds are in front of the moon.
light can be bent by gravity, so at a certain distance from a black hole, the event horizon, you would be able to look to the side and see the back of your own head. the telescope bit is only because the light still has to travel very far, so it'd still appear to be many miles away
I've never understood the need for a graviton. If a mass bends space-time in an expanding universe (in higher-than-3D geometry), and gravity is a result of that geometry (Einstein's general), then shouldn't we be looking for the interaction that binds all particles to the "fabric" of space-time? Universal acceleration and this "binding" force is all that we'd need to produce the effect of gravity - in lieu of a mediator that "communicates" gravity between two objects. It seems that this interaction would be present even if no significant gravity presents itself between two small or distant objects, because it's really an interaction with space-time itself.