+ellystripes It is very good system for traveling throught space more than "light speed". You no need increasing speed of ship, just bending space. And I hope this is first step for manipulate with gravitation.
ellystripes said: "I want to know what a ripple in space time would mean to this sandwich." This is actually a very intelligent and cogent question. Perhaps the penny hasn't dropped for you just yet, but think about it a bit longer.
ellystripes, firstly, forget gravity waves - it's not an accurate description. Gravitational Radiation imposes upon spacetime a 4 dimensional value. This means that A PULSE of gravitational radiation - perhaps from two orbiting Black Holes - propagating out from origin forces spacetime to expand as the pulse moves through it, but the ingredients and molecules in the sandwich want to remain together. Expanding spacetime can potentially rip apart the sandwich at the molecular level and atomic level as in the case of a Black Hole Event Horizon. Your entire body can be vaporised into a cloud - bones and all - given sufficiently expressive gravitational radiation. The sandwich question is actually an astonishingly good question to ask, in fact the entire line of questioning is sound. I don't think Cox truly know what a gravity wave is.
Max Headroom, I doubt that Brian Cox doesn't know what it is. I think he is trying hard to understand which "part of the alphabet" it is that the guy behind the camera doesn't get - maybe a bit too hard, so he is missing some of the obvious cues. Firstly, they start off talking about explaining things to the audience of the documentary whereas they should be talking about a common mindset first to have a common understanding of the actual question. Secondly, the guy compared himself to a surfer riding on a transverse wave whereas Cox had started out explaining longitudinal waves, so here is a mismatch of mindsets. And thirdly, the concept of "ripples in spacetime" is IMHO not understandable for anyone who hasn't grasped a fundamental concept of general relativity, i.e., Wheeler's "spacetime tells matter how to move, and matter tells spacetime how to curve." Now, putting it all together: For the audience, it wouldn't have mattered if they had explained a gravitational wave as longitudinal or transverse. Very simply speaking, if you looked at four-dimensional spacetime as a two-dimensional rubber sheet, gravitational waves would look like bubbles of air moving through a middle layer within the rubber, the size of the bubbles representing the magnitude of our four-dimensional spacetime vector
I think the confusion comes from the distinction (or lack thereof) between longitudinal and transverse waves. A water wave is transverse which is why you get an up and down motion but a sound wave is longitudinal which has no up and down. It's not clear which wave type a gravitational wave is from Brian's explanation.
There's something fascinating about watching a really smart person interact with a really stupid person, with no one giving a damn about how they come off. It's a bit like watching dwarf tossing.
You think that this producer is stupid, by asking questions, until it's a good enough explanation? Maybe you're afraid of asking questions, which is the sign of ignorance, not intelligence... Brian Cox clearly doesn't fully understand it himself, since he's getting visibly annoyed- you only truly understand something if you can properly explain it to someone else.
aahh i beg to differ. with my doctorate in communication systems from a tiny little university called Oxford, I (as Brian's producer) know exactly what Brian is jabbering on about. Just the thing is, the film isn't for me, or my clever chums. It is for a wide lay audience who quite possibly don't understand this stuff, so it is the job of the producer to get the clever chap in front of camera to explain stuff so that everyone can understand.
I beleive the tv Producer has a Doctorate from Oxford University and in this instance was only trying to get Bryan to explain something quite complex on camera so that a non scientific audience member could understand what on earth bryan is talkign about. I also believe said tv producer's doctorate involved fast fourier transfrom analysis of complex sound waves (just a hunch here) and so he knows exactly what Bryan is talking about. Said producer wanted Brain to explain things simply...
Just try watching the episode of the ABC show 'Q&A' to see how Cox pretends to know a lot more than he does when it comes to climate change. He makes a fool of himself, as he does in this video. Like I said, I like Brian and I'm glad he makes the docos he does, but he's essentially more of a poster boy for science who spends most his time doing tours and making TV shows than being a hard core physicist.
@@zedbaxter7101 my fisheries research professor at university was in Brian Cox's class at secondary school and apparently he failed his physics A level first time around!
Brian cox is awesome! A good way to think about what he is saying is to think about a trapoline and how the material stretches, bounces, and transfer energy through out the whole trampoline. I hope this helps.
Brian Cox seems to be quite slow in his head. Besides, if spacetime gets stretched, by what dimension do you measure the stretching? "Stretching" is a term used when describing the elongation and shortening of something regarding a dimension.
This, actually, was very helpful. Thankfully, I saw this after watching several other videos, but with a little bit of previous understanding, he gave me much more.
In all fairness to Cox, he is use to lecturing at a University, and so everyone he is teaching already knows exactly what a wave is from their A level Physics class.
@verticalsmurf The best way to visualize gravitational waves is to stretch out a slinky. If you look down the length of the slinky as you pound one end, you'll see the pressure wave bounce back and forth along the slinky. If you tape objects onto the slinky, near each other, you'll see them spreading apart and getting close together in succession. This represents the compression of atoms in a gravity wave. Btw i'm 31 not 16, and i just learned this 2 years ago.
I sympathise with Brian: he is clear and concise. The problem; which I think is very common; is where the supposed "experts" with language and communication (often writers, presenters and producers..) are not. They are the ones who can't cope when difficult concepts are clearly and precisely described. Their use of language is generally flowery pretty, but very poor semantically. If the producer was having such problems, why can't he explain what he doesn't understand?
in quantum gravity, gravitational waves can be though of as actual moving phonons of gravitons . just like, an EM wave is a phonon of photons moving though a virtual photon field, a gravity wave is a moving phonon of gravitons between the field of virtual gravitons Einstein calls space-time. both point of view are analogous, it's easier to explain in terms of particle and phonons or distorsions in fields, rather than bring the complex explanation of space-time wich people don't get .
Genuinely surprised by all the people in these comments who think the producer is rude / arguing, or even think this explanation of waves is simple enough for a general TV audience. Here's what's actually happening: the producer's trying to get him to explain gravitational waves in everyday terms... and he clearly can't, because physics is complicated, and science education is still difficult even for an expert. If you miss this basic emotional read, well -- tough.
Brian needs his own channel - Brian Cox Explains - it would be a bunch of maroons asking simple questions, getting clear answers and still not understanding. call it 'idiot shaming' and it will change the world.
I think there was confusion between the concept of coherent energy and mass. For example, a sound wave can be thought of as energy that impacts mass, then is thrown off by mass so that the coherent energy goes forward while the mass stays still. If your question is, "What is a wave", to some degree you are pre-supposing that there is some sort of "it", so it might be hard to come to grips with the fact that "it" is associated with different matter (ether?) at each instant.
At 2:17, Brian says that sound waves vibrate transverse to the direction of motion. They don't, they do exactly the opposite, they vibrate longitudinally, i.e. along the direction from which the disturbance originates.
Brian is confusing lateral and longitudinal waves. Still easy enough to understand. Spacetime is the medium, none of it travels, but a disturbance is propagated through it like a pressure fluctuation in air (a sound wave) causes adjacent air particles to be disturbed, which continues in an outward fashion from the source. The only unintuitive part about it is the fact that it is happening without matter interacting i.e. it happens to spacetime itself.
a longitudinal wave does also have transverse vibration in it, the individual air molecules vibrate transverse to the direction of travel, and that phonon of energy propagates forward as a longitudinal wave. the reason this is confusing is because it's newtonian mechanics, and we are trying to explain a relativistic event in newtonian terms, or a quantum event in newtonian terms, it simply can't be done without analogies.
This is an interesting look behind the scenes. It can be challenging to work with others on these kinds of projects. I can see it must have been difficult for Brian at times. This clip makes me appreciate the programs even more for I can see the struggle it must have been. The program was for the lay public and so having someone do what the producer is doing although annoying probably helped the show because they are seeking to make things clear to average viewers. We've all benefited.
the guy asking the question is trying to get Brian to answer a simple question so that a wide audience would understand. He is also tryign to wind up Brian (as we say in England) just for the sheer fun of seeing his angry face.
@SASNIGHTCRAWLER. Photons don't have 'Rest Mass', but they do have 'Inertial Mass', and this relates to energy momentum and curvature of spacetime as the photon flies through it. It's Inertial Mass is tiny, but real. In either case, both entities with or without mass are guided into a black hole because space and time are being dragged in to the black hole. But, space and time don't move, it is simply a change in the metric which creates the field of acceleration. Movement without Inertia.
@Bobbysl Remember the shows audience will be people who don't know much about physics, the producer was asking Brian to dumb down the explanation so that anyone can understand.
@vibins360 nope and yes. Sound in air propagates by longitudinal waves, but in solids and very high density liquids it propagates by both longitudinal and transversal waves. So bassically you're correct, but there's more into it :)
You're right, I was unprecise. Cox tells that spacetime contracts/expands, which is what a gravitational wave "does" to spacetime ;) The movement "through" spacetime is the wrong picture. Thanks for your correction, bassface182!
'Why is that not obvious?' LOL! Erm, I'm afraid it's just not for most people. Wave progression and what a wave does to the medium it's moving through is not at all intuitive - especially if you've never had it explained. Because disturbance of some sort is involved with wave motion, to most of us that infers physical movement of the medium....in the direction of the wave! But if this was true the medium would be pushed in front of the wave, and you'd have transport of something instead of just a momentary disturbance of that something. Wave motion's a difficult enough concept to grasp with familiar mediums - air, water, rock - so I can see the issue when talking about 'space time' (whatever that is). Anyway, a great post. Thank you for an insight into science vs TV production of science. Mick PS "Dr Brain Cox tries to explain to his tv producer what a gravitational wave is," is better. (Reported vs direct speech.)
Dear Brian, All you need to tell him is that when a crowd does "the wave", the people in the crowd aren't actually walking in the direction that the wave moves; they're simply moving up and down in a wave pattern. That's what a wave is. Also, to explain the effect of a gravity wave on the producer's sandwich: the sandwich sticks to the plate. The plate sticks to the table, and the table sticks to the floor which sticks to Earth. Ta-daa.
Gravitation waves change the volyme of the space or change the density of the space. Like soundwaves changes the density of the air. Correct explanation or?
2:25-2:30 "I want to know what a ripple in space-time would mean to this sandwich"2:30-2:40 Cox facial expression. LOL!!!!! I am sure anyone would have a hard time answering that guys question if they were treated this way, i myself would be stumped. You're intelligence just goes blank under such tense scrutiny.
I think the producer was wondering what happens to the objects within the space-time as it expands and contracts, but he wasn't able to articulate it. I think that's why he mentioned riding a water wave. Brian can't understand his low-level thinking, and the producer can't understand Brain's high-level thinking. Communication breakdown, perhaps?
lol,I think what's confusing the tv producer is that a wave on water pushing a surfboard or whatever -isn't- pushing it. the board is lifted up, its now on a slope, gravity causes it to slide down the slope, except that the part of the slope it's sliding down is also now rising. so it continually moves forwards. simple, but easily mixed up if you're not paying attention.
@JFSwifty yep. you have it right. and that is indeed where the confusion stems from. like BC says in the clip, it's more like sound pressure waves than anything else: at any point in space-time, the 'pressure' at any instant in time is rarely the same as it is an instant later. that point in space-time stays where it is but the pressure wave moves through it. might be easier to think of E-M waves, like from a radio transmitter. if that makes any sense...
It seems to me like a little conflict is necessary to thrash out the best way of tackling the explanation of difficult concepts to lay people. Different opinions and points of view will get a better result in cases like this, than everyone just nodding along.
I LOVE BRIAN COX. I think he's quality. And I really hope he can bring a mainstream audience to the idea that physics is actually REALLY impressive and interesting, rather than just geeky.
@Jiggerj01830 The simplest way I can put it (I'm no professor Cox), is think of a pool with oil on it, the water is spacetime, the oil is the matter of everything. A wave (gravity) goes through the water which stretches and compressed the water which does the same to the oil. Of course the denser clumps of oil will press deeper into the water and if you have taken a look at Relativity you will notice this is what Einstien says matter does to the fabric of time and is your gravitational field.
While space-time is rippling, this only means that curvature is rippling. It seems incorrect to suggest that rest-mass will be distorted. This seems like an important distinction that is overlooked when talking about gravitational waves. Many seem to assume that changes in the curvature of space-time apply to the dimensions of rest-mass. Therefore, you may notice a change in the perceived gravitational forces (accelerations of rest-mass reacting to space-time curvature) but you should not see length expansion or contraction. It might bend or lens photons but it wouldn't shorten or increase their travel distance (as measured in an L experiment). Photons would always be measured to travel at c. However, they might not be aimed like you thought they'd be. And I can't imagine that you'd ever be close enough to a gravitational wave source such the curvature changes would ever be of sufficient relativistic magnitude to have observed differences in time (seeing GPS out of whack). More: plus.google.com/+JonathanLangdale/posts/bRHdeSWxZRY .
Something that bugs me is the reification of mass. My understanding is that mass is a constant of proportionality relating incremental acceleration to differential force. As such, mass is not directly measurable, and as per special relativity, mass is certainly not invariant -- is a function of kinematic state. I challenge the notion of rest-mass as non-demonstrable idealization in the first place.
Jonathan Langdale Consider the solutions of the differential equation obtained by setting the magnitude of velocity to constant, i.e., setting the dot product of the velocity vector with itself to c*c. Only one of the solutions is a straight line, and that one can only exist in the absence of force, which is impossible in reality. Photons are accelerated by mass attraction and therefore alter course but do not slow down. Now, according to de Broglie, material objects have something in common with super high frequency photons. Also, I have no issue with mass-energy being invariant (it is, in the absence of energy exchange with an external system); just, mass is not.
Indirectly, yes. A photon is influenced by mass attraction, which causes it to change course. A photon does not "measure" anything per se; it reacts to the ambient gravity well according to its nature. My question to you is: is a photon mass attracted to the object which emitted it?
@vibins360 You're right- but I think Brian started to use the example of waves on water (transverse) then got flustered and threw in Sound waves (longitudinal) to explain that they don't "move" air, then went right back to talking about water waves without realizing his example now mixes up 2 different kinds of wave. The producer was asking pretty weird questions so I'm willing to let Brian off.
can i help, gravitation waves are only a theory that are currently being researched. gravitational waves are formed (theoretically) by movement or acceleration of mass objects ie binary stars that act like pulses.
What he is trying to describe is a longitudinal wave rather than a transverse wave. A 'Slinky' toy is a good tool for demonstrating longitudinal waves. The coils move together and apart as the energy travels through the toy. Similarly, space-time expands and contracts as the gravity wave propagates through it. Perpendicular lasers are expected to detect this phenomenon. (See LIGO & LISA)
I preferred Sagan rolling the ball on the rubber sheet. He made it understandable. Points of the sheet, NEAR where the ball went, got stretched, even though nothing physical passed through.
What would happen if 2 waves collided, would they go through each other with nothing happening, bounce of each other or would one take the other one out like a truck hitting a car?
do sound waves not affect the density of air, at all? or do water waves not affect the density of water, even slightly, as the waves are passing through..??
Brian I feel very proud of you. It seems to me you are close to comprehend how gravity works. But gravity is not a wave form and it doesn't have vibration is that simple it is more than wave form and vibration.
@SASNIGHTCRAWLER. The theory of gravity, General Relativity, is about how the spacetime field (field of acceleration) which moves into a massed object (black hole say), like carpet being pulled into a cellar, the furniture gets dragged down too. The converging furniture collisions are called tidal forces...molecules collide, heat up, and as in the case of Jupiter's moon 'Io', has volcanic activity.
Okay someone correct me if I'm wrong, but is it basically like if a ball went through a pool of water. The ball moves through the water, bending the water, ect. But because the ball, or wave, is made of such a weak force you don't notice it and you can't see it happen? That probably makes no sense...
Sound waves don't "vibrate transverse to the direction of motion", they are longitudinal waves - stretching and squashing of air molecules like he's demonstrating with his hands at the start - dunno why Brian Cox would get this wrong
what isnt so intuitive about what he is saying is that our perception of what a wave is doing is that it is propagating along a radial line from the center. THIS IS NOT THE CASE. What is happening is that particles are bouncing up and down in alternating intensities as the wave FORM moves outward and these particles are along a transverse axis to the wave form itself. Did this help?
2:09 Brian says that in a sound wave the particles vibrate transverse to the direction of motion, I thought sound was a longitudinal wave and the particles vibrated parallel to the direction of motion. Am I wrong?
@psychobollox What confuses me is how this process results in a continuous gravitational force. I think the producer is asking how a massive object, which apparently produces a disturbance in the fabric of spacetime, can cause that ripple to (i) come towards you (ii) hit you, then (iii) move away. I guess the answer is that the source is continually pulsing. But then why does the force never weaken or run out of energy? What is driving the force? That's what I don't get.
@JFSwifty A wave in space time is transverse to the direction they're traveling in. but in 3 dimensions. Space time is 4 dimensional remember. As far as I understand it, a wave in space time moves through the 3 dimensions, whilst moving at a steady pace through the 4th dimension which is perpendicular from the other 3 dimensions.
okay it seems theres a misunderstanding of terms here. Dr Cox assumes the producer know about the type of wave he's talking about specifically a longitudinal wave, but it seems the producer isn't aware waves don't only come in transverse waves, the one like on the oceans. Dr Cox didn't describe the different ways energy can propagate through a medium either perpendicular (transverse) or in the same direction the medium is travelling.
thansverse and longitudinal waves are taught to 14 year olds in this country upon their GCSE... if a producer of an astrophysics show is oblivious to this, then fuck them up their stupid ass
I watched the program yesterday. This particular part of the program, Cox admited was difficult to explain... but he explained it in a way that an unscientific head like me could understand... but now i know why.. after constant poking and prodding by the producer. This program seemed a continuation of David Malone's 'Testing God: Killing the creator' (2001).. where one of the main talking points was the laws of nature.. the possible options of where the laws came from, specifically gravity
LMAO Brian is seems irritated! Only saw him 1st time a couple of days ago and have been uplifted by his buoyancy and passion since. Wish there were more people around like him creating so much positive energy. Though it is good to see he has slightly negative traits and that his energy can subside too - shows there's hope for us all.
@vlatin1 Hi, sorry to jump in on your twos discussion, but I think the point Rebun24 was maming is that black holes have been directly observed, however you are right that there can never be any direct physical evidence for the black hole having an infinitely dense object at its centre. I think this is why cosmologists will still ALWAYS refer to them as black holes, and NEVER as singularities. A singularity is something for a particle physicist or a theoretical physicist to worry about.
(sorry for repeating that last bit). The problem is that Dr. Cox is so smart he's really having difficulty thinking that the producer is not understanding him. Non-scientific people can seem stupid when in fact it's their preconceptions that are at fault.
It reminds me of a little talk I had with my friend, a philosophy student, about something physics related but rather basic and at the end of me talking, waving my hands and doing silly sounds he just looked at me... (silence)... and said "and you actually believe it?!" :D
@BinaryStars100 They are compression waves but they can also be traverse waves when transmitted through solids. I think he just got his words mixed up because he went from talking about water to sound...plus he was on a rant. I think we can forgive him for that little slip up! :-)
@guitarpedant I think he was trying to relate back to the producer's example of water waves as he knew how he was visualising it- I'm sure he knows his waves!
I assume the question asker was confused about what is actually moving. An example would be the surface of water with a toy boat on it. The boat, and therefore the water, does not move from it's original position. The waves are the objects that are moving. This means that space is not moving...waves are moving THROUGH space.
The biggest problem EVERY description faces is that there is a fundamental difference. Gravity waves are simply changes in values of a metric tensor BUT are subject to RELATIVE viewpoints too. You gotta know metrics first.
@Mavrik347 Thanks for the info, Mavrik. Please bear with me for one more ignorant question: You say that space-time is the equivalent of my water. The ingredients of water is hydrogen and oxygen. What are the ingredients of space-time? I know you'll want to say space and time, but this doesn't say anything. We can describe what everything is in the universe (like: sound: a wave that travels through air...) so, what is space-time made of?
Great extrapolation of the issue. Actually I would have liked to hear more of that cause it is quite fascinating subject; what really is happening when electromagnetic wave is moving... This is ... like ... the most interesting videos ever; a super physicist explaining a mundane thing (mundane to him) ;-)
Wow. We all have some difficulty understanding concepts from theoretical physics, but this is like an interview by Ali G, except none of the humour.
"I want to know what a ripple in space time would mean to this sandwich."
I mean, honestly....
+ellystripes It is very good system for traveling throught space more than "light speed". You no need increasing speed of ship, just bending space. And I hope this is first step for manipulate with gravitation.
ellystripes said: "I want to know what a ripple in space time would mean to this sandwich."
This is actually a very intelligent and cogent question. Perhaps the penny hasn't dropped for you just yet, but think about it a bit longer.
Zed Baxter Thank you! Your condescension is appreciated.
ellystripes, firstly, forget gravity waves - it's not an accurate description.
Gravitational Radiation imposes upon spacetime a 4 dimensional value. This means that A PULSE of gravitational radiation - perhaps from two orbiting Black Holes - propagating out from origin forces spacetime to expand as the pulse moves through it, but the ingredients and molecules in the sandwich want to remain together. Expanding spacetime can potentially rip apart the sandwich at the molecular level and atomic level as in the case of a Black Hole Event Horizon.
Your entire body can be vaporised into a cloud - bones and all - given sufficiently expressive gravitational radiation.
The sandwich question is actually an astonishingly good question to ask, in fact the entire line of questioning is sound. I don't think Cox truly know what a gravity wave is.
Max Headroom, I doubt that Brian Cox doesn't know what it is. I think he is trying hard to understand which "part of the alphabet" it is that the guy behind the camera doesn't get - maybe a bit too hard, so he is missing some of the obvious cues. Firstly, they start off talking about explaining things to the audience of the documentary whereas they should be talking about a common mindset first to have a common understanding of the actual question. Secondly, the guy compared himself to a surfer riding on a transverse wave whereas Cox had started out explaining longitudinal waves, so here is a mismatch of mindsets. And thirdly, the concept of "ripples in spacetime" is IMHO not understandable for anyone who hasn't grasped a fundamental concept of general relativity, i.e., Wheeler's "spacetime tells matter how to move, and matter tells spacetime how to curve." Now, putting it all together: For the audience, it wouldn't have mattered if they had explained a gravitational wave as longitudinal or transverse. Very simply speaking, if you looked at four-dimensional spacetime as a two-dimensional rubber sheet, gravitational waves would look like bubbles of air moving through a middle layer within the rubber, the size of the bubbles representing the magnitude of our four-dimensional spacetime vector
"Are you being weird now?" oh god that was so funny
I think the confusion comes from the distinction (or lack thereof) between longitudinal and transverse waves. A water wave is transverse which is why you get an up and down motion but a sound wave is longitudinal which has no up and down. It's not clear which wave type a gravitational wave is from Brian's explanation.
"I can`t see that as a wave..." "tough"
love brian cox
"a...are you being weird now...?" ahahhaahhhhahahahahah
There's something fascinating about watching a really smart person interact with a really stupid person, with no one giving a damn about how they come off. It's a bit like watching dwarf tossing.
+EGarrett01 You could write Simon Cowel's remarks to really bad contestants.
You think that this producer is stupid, by asking questions, until it's a good enough explanation? Maybe you're afraid of asking questions, which is the sign of ignorance, not intelligence...
Brian Cox clearly doesn't fully understand it himself, since he's getting visibly annoyed- you only truly understand something if you can properly explain it to someone else.
The person's counter explanations show no signs of progress or probing of Cox's explanation. That is a sign of a dumb person.
the director is not an idiot. he was just 'training' brian to get the goods needed for the film.
as a producer for science programme, shouldn't he be scientifically literate?
aahh i beg to differ. with my doctorate in communication systems from a tiny little university called Oxford, I (as Brian's producer) know exactly what Brian is jabbering on about. Just the thing is, the film isn't for me, or my clever chums. It is for a wide lay audience who quite possibly don't understand this stuff, so it is the job of the producer to get the clever chap in front of camera to explain stuff so that everyone can understand.
I beleive the tv Producer has a Doctorate from Oxford University and in this instance was only trying to get Bryan to explain something quite complex on camera so that a non scientific audience member could understand what on earth bryan is talkign about. I also believe said tv producer's doctorate involved fast fourier transfrom analysis of complex sound waves (just a hunch here) and so he knows exactly what Bryan is talking about. Said producer wanted Brain to explain things simply...
Usually Brian Cox is the MOST patient man in the world lol
+assassin8or Or maybe he does lots of 'takes'. LOL
Just try watching the episode of the ABC show 'Q&A' to see how Cox pretends to know a lot more than he does when it comes to climate change. He makes a fool of himself, as he does in this video. Like I said, I like Brian and I'm glad he makes the docos he does, but he's essentially more of a poster boy for science who spends most his time doing tours and making TV shows than being a hard core physicist.
@@zedbaxter7101 my fisheries research professor at university was in Brian Cox's class at secondary school and apparently he failed his physics A level first time around!
@@zedbaxter7101 nope but thanks for your 6 year old comment that didn't really do anything.
Brian cox is awesome! A good way to think about what he is saying is to think about a trapoline and how the material stretches, bounces, and transfer energy through out the whole trampoline. I hope this helps.
now I'd like to see Nigel Tufnel's version of this concept!
Brian Cox seems to be quite slow in his head.
Besides, if spacetime gets stretched, by what dimension do you measure the stretching?
"Stretching" is a term used when describing the elongation and shortening of something regarding a dimension.
This, actually, was very helpful. Thankfully, I saw this after watching several other videos, but with a little bit of previous understanding, he gave me much more.
In all fairness to Cox, he is use to lecturing at a University, and so everyone he is teaching already knows exactly what a wave is from their A level Physics class.
I love this so much. Brian Cox, as always is explaining something wonderfully and when some guy argues with him... TOUGH!
@verticalsmurf The best way to visualize gravitational waves is to stretch out a slinky. If you look down the length of the slinky as you pound one end, you'll see the pressure wave bounce back and forth along the slinky. If you tape objects onto the slinky, near each other, you'll see them spreading apart and getting close together in succession. This represents the compression of atoms in a gravity wave. Btw i'm 31 not 16, and i just learned this 2 years ago.
A wave goes through a medium. The medium itself doesnt go anywhere...it that it?
I sympathise with Brian: he is clear and concise.
The problem; which I think is very common; is where the supposed "experts" with language and communication (often writers, presenters and producers..) are not. They are the ones who can't cope when difficult concepts are clearly and precisely described. Their use of language is generally flowery pretty, but very poor semantically. If the producer was having such problems, why can't he explain what he doesn't understand?
in quantum gravity, gravitational waves can be though of as actual moving phonons of gravitons .
just like, an EM wave is a phonon of photons moving though a virtual photon field, a gravity wave is a moving phonon of gravitons between the field of virtual gravitons Einstein calls space-time.
both point of view are analogous, it's easier to explain in terms of particle and phonons or distorsions in fields, rather than bring the complex explanation of space-time wich people don't get .
Genuinely surprised by all the people in these comments who think the producer is rude / arguing, or even think this explanation of waves is simple enough for a general TV audience. Here's what's actually happening: the producer's trying to get him to explain gravitational waves in everyday terms... and he clearly can't, because physics is complicated, and science education is still difficult even for an expert. If you miss this basic emotional read, well -- tough.
Brian needs his own channel - Brian Cox Explains - it would be a bunch of maroons asking simple questions, getting clear answers and still not understanding.
call it 'idiot shaming' and it will change the world.
I think he was wondering why you can't feel these waves stretching space and time like he can feel the wave when he is surfing??
I think there was confusion between the concept of coherent energy and mass. For example, a sound wave can be thought of as energy that impacts mass, then is thrown off by mass so that the coherent energy goes forward while the mass stays still. If your question is, "What is a wave", to some degree you are pre-supposing that there is some sort of "it", so it might be hard to come to grips with the fact that "it" is associated with different matter (ether?) at each instant.
At 2:17, Brian says that sound waves vibrate transverse to the direction of motion. They don't, they do exactly the opposite, they vibrate longitudinally, i.e. along the direction from which the disturbance originates.
Brian is confusing lateral and longitudinal waves. Still easy enough to understand. Spacetime is the medium, none of it travels, but a disturbance is propagated through it like a pressure fluctuation in air (a sound wave) causes adjacent air particles to be disturbed, which continues in an outward fashion from the source. The only unintuitive part about it is the fact that it is happening without matter interacting i.e. it happens to spacetime itself.
a longitudinal wave does also have transverse vibration in it, the individual air molecules vibrate transverse to the direction of travel, and that phonon of energy propagates forward as a longitudinal wave.
the reason this is confusing is because it's newtonian mechanics, and we are trying to explain a relativistic event in newtonian terms, or a quantum event in newtonian terms, it simply can't be done without analogies.
This is an interesting look behind the scenes. It can be challenging to work with others on these kinds of projects. I can see it must have been difficult for Brian at times. This clip makes me appreciate the programs even more for I can see the struggle it must have been. The program was for the lay public and so having someone do what the producer is doing although annoying probably helped the show because they are seeking to make things clear to average viewers. We've all benefited.
the guy asking the question is trying to get Brian to answer a simple question so that a wide audience would understand. He is also tryign to wind up Brian (as we say in England) just for the sheer fun of seeing his angry face.
I'm just glad to know that there are issues when explaining physics concepts even for Dr Cox!
@SASNIGHTCRAWLER.
Photons don't have 'Rest Mass', but they do have 'Inertial Mass', and this relates to energy momentum and curvature of spacetime as the photon flies through it. It's Inertial Mass is tiny, but real. In either case, both entities with or without mass are guided into a black hole because space and time are being dragged in to the black hole. But, space and time don't move, it is simply a change in the metric which creates the field of acceleration. Movement without Inertia.
@Bobbysl Remember the shows audience will be people who don't know much about physics, the producer was asking Brian to dumb down the explanation so that anyone can understand.
The look on his face when the producer asks "I want to know what a ripple in spacetime would mean to this sandwich" is absolutely priceless
Thanks for sharing this. Really interesting and helpful for me.
@vibins360 nope and yes. Sound in air propagates by longitudinal waves, but in solids and very high density liquids it propagates by both longitudinal and transversal waves. So bassically you're correct, but there's more into it :)
Sound waves are not transverse but are longitudinal waves, waves which the motion of vibratory disturbance is parallel to the direction of propagation
Just wanted to say thank you for sharing these outakes. It's great to see a very real conversation, that also make me laugh.
im curious to hear what the other guys were about to say before the video cut out
"Tough", wow i lost myself at that moment. As a physicist i feel that same way every time i talk to my friends, im just not so blunt.
we did include this scene in cut down form - in that brian was indeed struggling to find the right words to explain the process in a simple way.
It would be useful if he used the traffic jam scenario. That explain waves quite well.
You're right, I was unprecise. Cox tells that spacetime contracts/expands, which is what a gravitational wave "does" to spacetime ;)
The movement "through" spacetime is the wrong picture. Thanks for your correction, bassface182!
Brian Cox has the patience of a very patient thing!
'Why is that not obvious?' LOL! Erm, I'm afraid it's just not for most people.
Wave progression and what a wave does to the medium it's moving through is not at all intuitive - especially if you've never had it explained. Because disturbance of some sort is involved with wave motion, to most of us that infers physical movement of the medium....in the direction of the wave! But if this was true the medium would be pushed in front of the wave, and you'd have transport of something instead of just a momentary disturbance of that something.
Wave motion's a difficult enough concept to grasp with familiar mediums - air, water, rock - so I can see the issue when talking about 'space time' (whatever that is).
Anyway, a great post. Thank you for an insight into science vs TV production of science.
Mick
PS "Dr Brain Cox tries to explain to his tv producer what a gravitational wave is," is better. (Reported vs direct speech.)
Dear Brian,
All you need to tell him is that when a crowd does "the wave", the people in the crowd aren't actually walking in the direction that the wave moves; they're simply moving up and down in a wave pattern.
That's what a wave is.
Also, to explain the effect of a gravity wave on the producer's sandwich: the sandwich sticks to the plate. The plate sticks to the table, and the table sticks to the floor which sticks to Earth. Ta-daa.
Gravitation waves change the volyme of the space or change the density of the space. Like soundwaves changes the density of the air. Correct explanation or?
2:25-2:30 "I want to know what a ripple in space-time would mean to this sandwich"2:30-2:40 Cox facial expression. LOL!!!!! I am sure anyone would have a hard time answering that guys question if they were treated this way, i myself would be stumped. You're intelligence just goes blank under such tense scrutiny.
I think the producer was wondering what happens to the objects within the space-time as it expands and contracts, but he wasn't able to articulate it. I think that's why he mentioned riding a water wave. Brian can't understand his low-level thinking, and the producer can't understand Brain's high-level thinking. Communication breakdown, perhaps?
lol,I think what's confusing the tv producer is that a wave on water pushing a surfboard or whatever -isn't- pushing it. the board is lifted up, its now on a slope, gravity causes it to slide down the slope, except that the part of the slope it's sliding down is also now rising. so it continually moves forwards. simple, but easily mixed up if you're not paying attention.
Very, very excellently put.
@JFSwifty
yep. you have it right.
and that is indeed where the confusion stems from. like BC says in the clip, it's more like sound pressure waves than anything else: at any point in space-time, the 'pressure' at any instant in time is rarely the same as it is an instant later. that point in space-time stays where it is but the pressure wave moves through it. might be easier to think of E-M waves, like from a radio transmitter. if that makes any sense...
It seems to me like a little conflict is necessary to thrash out the best way of tackling the explanation of difficult concepts to lay people. Different opinions and points of view will get a better result in cases like this, than everyone just nodding along.
I LOVE BRIAN COX. I think he's quality. And I really hope he can bring a mainstream audience to the idea that physics is actually REALLY impressive and interesting, rather than just geeky.
@Jiggerj01830 The simplest way I can put it (I'm no professor Cox), is think of a pool with oil on it, the water is spacetime, the oil is the matter of everything. A wave (gravity) goes through the water which stretches and compressed the water which does the same to the oil.
Of course the denser clumps of oil will press deeper into the water and if you have taken a look at Relativity you will notice this is what Einstien says matter does to the fabric of time and is your gravitational field.
You should try to explain why is that gravity moves to begin with Mr Cox.
While space-time is rippling, this only means that curvature is rippling. It seems incorrect to suggest that rest-mass will be distorted. This seems like an important distinction that is overlooked when talking about gravitational waves. Many seem to assume that changes in the curvature of space-time apply to the dimensions of rest-mass.
Therefore, you may notice a change in the perceived gravitational forces (accelerations of rest-mass reacting to space-time curvature) but you should not see length expansion or contraction. It might bend or lens photons but it wouldn't shorten or increase their travel distance (as measured in an L experiment). Photons would always be measured to travel at c. However, they might not be aimed like you thought they'd be.
And I can't imagine that you'd ever be close enough to a gravitational wave source such the curvature changes would ever be of sufficient relativistic magnitude to have observed differences in time (seeing GPS out of whack).
More:
plus.google.com/+JonathanLangdale/posts/bRHdeSWxZRY
.
Something that bugs me is the reification of mass. My understanding is that mass is a constant of proportionality relating incremental acceleration to differential force. As such, mass is not directly measurable, and as per special relativity, mass is certainly not invariant -- is a function of kinematic state. I challenge the notion of rest-mass as non-demonstrable idealization in the first place.
David Chako What is a lensed photon measuring as it curves near the Sun?
Jonathan Langdale Consider the solutions of the differential equation obtained by setting the magnitude of velocity to constant, i.e., setting the dot product of the velocity vector with itself to c*c.
Only one of the solutions is a straight line, and that one can only exist in the absence of force, which is impossible in reality. Photons are accelerated by mass attraction and therefore alter course but do not slow down.
Now, according to de Broglie, material objects have something in common with super high frequency photons.
Also, I have no issue with mass-energy being invariant (it is, in the absence of energy exchange with an external system); just, mass is not.
David Chako Was that an answer to my question?
Indirectly, yes. A photon is influenced by mass attraction, which causes it to change course. A photon does not "measure" anything per se; it reacts to the ambient gravity well according to its nature.
My question to you is: is a photon mass attracted to the object which emitted it?
@vibins360 You're right- but I think Brian started to use the example of waves on water (transverse) then got flustered and threw in Sound waves (longitudinal) to explain that they don't "move" air, then went right back to talking about water waves without realizing his example now mixes up 2 different kinds of wave. The producer was asking pretty weird questions so I'm willing to let Brian off.
can i help, gravitation waves are only a theory that are currently being researched.
gravitational waves are formed (theoretically) by movement or acceleration of mass objects ie binary stars that act like pulses.
What he is trying to describe is a longitudinal wave rather than a transverse wave. A 'Slinky' toy is a good tool for demonstrating longitudinal waves. The coils move together and apart as the energy travels through the toy. Similarly, space-time expands and contracts as the gravity wave propagates through it. Perpendicular lasers are expected to detect this phenomenon. (See LIGO & LISA)
I preferred Sagan rolling the ball on the rubber sheet. He made it understandable. Points of the sheet, NEAR where the ball went, got stretched, even though nothing physical passed through.
What would happen if 2 waves collided, would they go through each other with nothing happening, bounce of each other or would one take the other one out like a truck hitting a car?
patience and tolerance combined with sheer and utter fucking genius - sigh!
do sound waves not affect the density of air, at all? or do water waves not affect the density of water, even slightly, as the waves are passing through..??
Brian I feel very proud of you. It seems to me you are close to comprehend how gravity works. But gravity is not a wave form and it doesn't have vibration is that simple it is more than wave form and vibration.
@SASNIGHTCRAWLER.
The theory of gravity, General Relativity, is about how the spacetime field (field of acceleration) which moves into a massed object (black hole say), like carpet being pulled into a cellar, the furniture gets dragged down too. The converging furniture collisions are called tidal forces...molecules collide, heat up, and as in the case of Jupiter's moon 'Io', has volcanic activity.
Okay someone correct me if I'm wrong, but is it basically like if a ball went through a pool of water. The ball moves through the water, bending the water, ect. But because the ball, or wave, is made of such a weak force you don't notice it and you can't see it happen?
That probably makes no sense...
Sound waves don't "vibrate transverse to the direction of motion", they are longitudinal waves - stretching and squashing of air molecules like he's demonstrating with his hands at the start - dunno why Brian Cox would get this wrong
what isnt so intuitive about what he is saying is that our perception of what a wave is doing is that it is propagating along a radial line from the center. THIS IS NOT THE CASE. What is happening is that particles are bouncing up and down in alternating intensities as the wave FORM moves outward and these particles are along a transverse axis to the wave form itself. Did this help?
2:09 Brian says that in a sound wave the particles vibrate transverse to the direction of motion, I thought sound was a longitudinal wave and the particles vibrated parallel to the direction of motion. Am I wrong?
@psychobollox
What confuses me is how this process results in a continuous gravitational force. I think the producer is asking how a massive object, which apparently produces a disturbance in the fabric of spacetime, can cause that ripple to (i) come towards you (ii) hit you, then (iii) move away.
I guess the answer is that the source is continually pulsing. But then why does the force never weaken or run out of energy? What is driving the force?
That's what I don't get.
@JFSwifty A wave in space time is transverse to the direction they're traveling in. but in 3 dimensions. Space time is 4 dimensional remember. As far as I understand it, a wave in space time moves through the 3 dimensions, whilst moving at a steady pace through the 4th dimension which is perpendicular from the other 3 dimensions.
okay it seems theres a misunderstanding of terms here. Dr Cox assumes the producer know about the type of wave he's talking about specifically a longitudinal wave, but it seems the producer isn't aware waves don't only come in transverse waves, the one like on the oceans. Dr Cox didn't describe the different ways energy can propagate through a medium either perpendicular (transverse) or in the same direction the medium is travelling.
thansverse and longitudinal waves are taught to 14 year olds in this country upon their GCSE...
if a producer of an astrophysics show is oblivious to this, then fuck them up their stupid ass
I watched the program yesterday. This particular part of the program, Cox admited was difficult to explain... but he explained it in a way that an unscientific head like me could understand... but now i know why.. after constant poking and prodding by the producer. This program seemed a continuation of David Malone's 'Testing God: Killing the creator' (2001).. where one of the main talking points was the laws of nature.. the possible options of where the laws came from, specifically gravity
A moving sphere which expands and contracts would be one way to visualise a spacetime wave.
LMAO Brian is seems irritated! Only saw him 1st time a couple of days ago and have been uplifted by his buoyancy and passion since. Wish there were more people around like him creating so much positive energy. Though it is good to see he has slightly negative traits and that his energy can subside too - shows there's hope for us all.
like a caterpillar moving along? is that close to how it is?
@vlatin1 Hi, sorry to jump in on your twos discussion, but I think the point Rebun24 was maming is that black holes have been directly observed, however you are right that there can never be any direct physical evidence for the black hole having an infinitely dense object at its centre. I think this is why cosmologists will still ALWAYS refer to them as black holes, and NEVER as singularities. A singularity is something for a particle physicist or a theoretical physicist to worry about.
Haha, "Are you just being weird now?" Dr. Cox, you are a patient man.
(sorry for repeating that last bit). The problem is that Dr. Cox is so smart he's really having difficulty thinking that the producer is not understanding him. Non-scientific people can seem stupid when in fact it's their preconceptions that are at fault.
This is a deleted scene from Alan Partridge, right?
it literally doesn't even correlate with a single aspect of patridge...
It reminds me of a little talk I had with my friend, a philosophy student, about something physics related but rather basic and at the end of me talking, waving my hands and doing silly sounds he just looked at me... (silence)... and said "and you actually believe it?!" :D
Where are these outtakes from?
He just doesn't get it, people. We've all had those moments.
So true.
i think you had more of these moments than most
@BinaryStars100 They are compression waves but they can also be traverse waves when transmitted through solids. I think he just got his words mixed up because he went from talking about water to sound...plus he was on a rant. I think we can forgive him for that little slip up! :-)
@guitarpedant
I think he was trying to relate back to the producer's example of water waves as he knew how he was visualising it- I'm sure he knows his waves!
@PolarSquid Longitudinal waves don't move media, either (beyond a little bit).
You tell em brian. I understand it . How can anyone not
would it not be easier to explain it like flicking a cable, ripples move down but the cable doesnt move anywhere, it stays in your hand
I assume the question asker was confused about what is actually moving. An example would be the surface of water with a toy boat on it. The boat, and therefore the water, does not move from it's original position. The waves are the objects that are moving. This means that space is not moving...waves are moving THROUGH space.
Did you deliberately write "Brain" Cox in the description? :)
I understand everything that he says perfectly. I'm 16. Is it really that hard to understand?
The biggest problem EVERY description faces is that there is a fundamental difference. Gravity waves are simply changes in values of a metric tensor BUT are subject to RELATIVE viewpoints too. You gotta know metrics first.
the gravitational waves cause the stretching and contraction. the stretching and contraction isn't the actual wave but the effect the wave causes
@Mavrik347 Thanks for the info, Mavrik. Please bear with me for one more ignorant question: You say that space-time is the equivalent of my water. The ingredients of water is hydrogen and oxygen. What are the ingredients of space-time? I know you'll want to say space and time, but this doesn't say anything. We can describe what everything is in the universe (like: sound: a wave that travels through air...) so, what is space-time made of?
Great extrapolation of the issue. Actually I would have liked to hear more of that cause it is quite fascinating subject; what really is happening when electromagnetic wave is moving... This is ... like ... the most interesting videos ever; a super physicist explaining a mundane thing (mundane to him) ;-)
It's funny to see Brian Cox angry, he is usually portrayed as a saint, so good to see he can get pissed. He is a legend though
Ok, I think that those guys just wanted to hear whether the hamburger would get smashed/destroyed by the wave or it would just shrink and expand back.
you'd be right in your assumption about his producer, ie me. and we did workshop, and we've made a brand new film exploring the nature of time.