Can gravitational waves INTERFERE with each other?

[@frasercain]

Thank you, I get this question all the time too.

[@DylanStone-w4s]

So little pieces of smoke energy are inside one field and all these little pieces that make up this field are different condensities so when they collide they can pack into each other... Becoming more condensed in pulling on the second field that's around the first field condensing it because it compacts into that space because it connects then what we see from gravitation anyway... Is the field being created by the first field when it becomes condense enough to condense the second field it also pulls in other little pieces... From its field that are different condensities.... Creating a field around the graviton that acts like an electromagnetic field....👽😇🤣🙄😜...Basically the reason we see everything I talked about in the other videos... Or audios... Is whenever you get closer to a field of gravity .... Other gravitational pulls become more condensed because the other gravitational field starts to condense it more and we can say this happens because they're different little pieces.... condensing the other gravity around it pulling in the object...

[@DylanStone-w4s]

If ultimately you think the election was hacked what's the point in promoting yourself.. for president when you didn't win the last time you think you'll be able to rig the election this time... or you're going to catch them ringing the election this time because what's the stop them from doing it again if they didn't get caught

[@weeblewonder]

Praying for all these Better Help contracts to run out on KZbin channels. Tired of feeling gaslit by a terrible org being promoted as if they're actually helpful.

[@Koroistro]

And note that they go for autoritative sciency channels. However they go on those that don't have the knowledge base to understand the ethical obligations actual therapists have.

[@mal2ksc]

Almost makes you wish for Raid Shadow Legends to come back, doesn't it?

[@kurtcraig3421]

if i see one more better help vid i'm going to need some for my constant self evaluation anxiety. maybe that's their business strategy.

[@kurtcraig3421]

@@mal2ksc thanks for ptsd trigger.

[@Laff700]

@@mal2ksc Maybe we were too harsh on them. At the end of the day, they did give KZbinrs a lot of money, and couldn't've been _that_ sinister.

[@KB-vq6li]

Love the fact this all came from a viewers' question. Shows that you take your community seriously and I love that.

[@pshalleck]

My favorite part of the introduction to the question is that, despite having an intuitive assumption about the answer, she recognized the importance of asking it and how much we still have to test and prove.

[@DrBecky]

Thanks. Admittedly I get a lot of emails like that and I can't reply to them all. Indeed, I didn't even reply to that one but I will now with a "surprise! I made a video" message haha

[@John.0z]

You beat me to that comment. Really well done Becky!

[@jamesbailey4581]

yup, good job Larry!

[@executor893]

I wonder what percentage of the emails she receives are crackpot theory ones? 90%?

[@miallo]

Hey Becky! Thank you very much for your great science communication! The way you present even the most complex topics to a broad audience is truly astonishing. First of all: I know this is not your main area of research, so hopefully you don't feel like your valuable time is wasted by another one of these crazy theories you will get every day ^^ If this is the case: I'm sorry and please just ignore this... In this video you talked again about the way the path of light is bent by gravity. For the cosmic distance ladder having a good model of it seems essential. Since both my Bachelors and Masters Thesis involved optics/lasers (yeah I was one of those solid state physics guys ^^), it made me wonder if there could be additional factors that might have been unaccounted for. Especially for the basic parallax measurement which by propagation of uncertainty would probably have a major impact on the more distant stages. My best guess of the distribution of the interplanetary medium in the outer solar system is that it is more or less radially symmetric and probably tailors off the more you go outwards (since I left academia I don't have access to many academic journals and (probably also because I was looking for the wrong words) I could not find papers on this for the outer solar system). Because a difference in density will result in a different refractive index this seems very related to gradient-index optics. This is obviously well known in astronomy e.g. with the earths atmosphere acting as a GRIN lens when you can still see the sun even if it is technically already below the horizon (=> unrelated: maybe a nice fun fact to explain in a Night Sky News when applicable). The "Gaia Data Release 2" article/paper [1] does not seem to take this into account. Is this just because the effect is negligible? It is hard to do a back of the envelope calculation because obviously compared to a usual optics lab the gradient in refractive index is minuscule but the distances are gigantic, so a simple ray transfer matrix analysis was basically useless with the data I have. Do you know anything about this from the top of your head? Thank you again for your great science communication! Michael [1] doi.org/10.1051/0004-6361/201833051

[@Morganstein-Railroad]

You have the ability to explain the most complex and Difficult subject matter in a way that the general public can interpret. Combine this with a very approachable personality and easy going attitude that you display in your videos and we have something special. I am 62 Years old - I have no real interest in you on a personal level other than what I have said. Having said that, If you were my daughter, I would be extremely proud of your acheivements, and your overall persona. That is why I love your work, and acheive great pleasure in watching these videos.. Thank you, Doctor Becky.

[@rdbasha5184]

If a field interferes with itself, it DOES NOT mean that the particle interacts with itself. For example, in pure electromagnetism, light interferes with itself, like any wave, but photons do not interact with photons. In the real world, photons do interact indirectly, but that is an EXTREMELY minor effect, and has nothing to do with the constructive/destructive interferences that we see in lasers. So whether gravitons interfere would not be any indication that they interact with themselves. We do, however, have many other reasons to belive that gravitons self-interact.

[@Lucius_Chiaraviglio]

My understand of she was saying is that gravitational waves would interact in ways that would be potentially detectable(*) as being different from how electromagnetic waves interfere. (*)With the caveat that LIGO and its relatives before the latest upgrade were not sensitive enough for this, and that upgraded LIGO might be sensitive enough, but not guaranteed.

[@danieljensen2626]

I think she's being a little loosey-goosey with her terminology because this is a public science communication video and not a technical paper. Her example of gravitational waves apparently being gravitationally lensed is a clear example though, EM waves DO NOT do that. She's saying interference but its clear in most of the cases she actually means interaction.

[@Lucius_Chiaraviglio]

@@danieljensen2626 EM waves do get gravitationally lensed. The question is whether gravitational waves lens each other -- this is predicted to happen and to influence how they interfere with each other, but more sensitive instrumentation is needed to detect it.

[@bikerfirefarter7280]

Assuming there are such things as 'gravitons'.

[@Lucius_Chiaraviglio]

@@bikerfirefarter7280 Good point -- at this point, we have neither proven nor disproven the existence of gravitons. If gravity is purely the manifestation of curvature of spacetime and not a force at all, like Sabine Hossenfelder says, then it would have no need for a force-carrying particle, and might well be a completely non-quantum phenomenon that will NEVER unify with the Standard Model forces.

[@robspiess]

@4:52 is it "deconstructive" interference? I've always heard it as "destructive" interference.

[@garethdean6382]

Both are used, though 'deconstructive' as the opposite of constructive is the more correct.

[@threeMetreJim]

My spelling checker also does not like the word "deconstructive".

[@Chris_Goulet]

You're right: every Google search suggestion for "deconstructive interference..." is corrected to "destructive interference..."

[@michaelsommers2356]

It's just a word! It makes no difference to the content.

[@robspiess]

@@michaelsommers2356 Sorry, I just wanted to know if I was using the wrong word or if I should be using one or the other word in a specific context.

[@moocowpong1]

I think you’re conflating *interference* and *self-interaction* here a little. In Maxwell’s equation, two light beams will interfere with each other, but they won’t *interact*-if they cross, they will each continue on after the crossing identically to if the other hadn’t been there, with no deflection or scattering. Interference is possible without interaction. Gravitational waves do interact with gravity, as you said, but that’s a different phenomenon from interference.

[@francom6230]

YES.. same with sound.. she's not entirely correct about "noise cancelation" or photon interactions.. she's making videos.. 🤔

[@QuicksilverSG]

Moreover, the quantum interference patterns observed in double-slit experiments are produced by the summation of complex-valued components in the quantum wave function. This type of interference does not apply to gravitational waves, simply because quantum mechanics does not apply to gravity.

[@moocowpong1]

@@QuicksilverSG even water waves and sound waves have interference patterns though. gravitational waves should exhibit interference simply due to being waves

[@QuicksilverSG]

@@moocowpong1 - The difference is that water and sound waves travel through physical media (water and air). Subatomic particles propagate via quantum fields. But with gravity there is no medium, there is only curvature of the spacetime metric (according to Einstein).

[@objective_psychology]

There is no such thing as separate self-interaction since gravity is not a true force. If quantum physics has taught us anything it's that gravitons probably don't exist.

[@IMortage]

Stop promoting BetterHelp, please. They've gained a (well deserved) shoddy reputation.

[@tyresefarrell]

useless as anything they are, solve more issues for yourself by going and buying a mcdonalds to make you feel better for the night xD

[@raphaelnjoroge1145]

Let her get her money

[@Kivikesku]

It's probably unwise to trust this company with sensitive information about your mental health.

[@Reinforce_Zwei]

Say it with me, CONTRACTED SEGMENT. She has no damn choice but to do the ad-read until the contract is over, unless you're going to pony up the money she'd lose for backing out. It isn't as simple as them sponsoring just a single video, they contract for the whole year or even longer sometimes.

[@slabrankle9588]

Also, the ordinary stresses and anxieties of adult life shouldn't require professional help. Bad precedent.

[@Stephen_Lafferty]

14:22 - I love the sneaky Doctor Who reference right at the end of a discussion of a highly complex scientific topic! :D

[@adrianbruce2963]

At the end? I was hearing Mavity in my head all through!

[@spacelem]

I hate being pedantic, but Newton didn't come up with the word "gravity", he reinterpreted gravity as a force rather than a natural quality. Everyone else was enjoying that (otherwise fantastic) episode of Doctor Who, while I was sitting there going "but Newton didn't..."

[@jwag82]

@@spacelemFurthermore, Newton lacked the mavitas to change the word all the way back in Ancient Rome.

[@Manzarek2009]

Meh… gravity, mavity, schmativy… the truth is with the interconnectedness of gravity, strength, weakness, electromagnetism, time, and space, the whole thing is just a big ball of wibbly, wobbly, timey, wimey… stuff.

[@atlantisvelforening]

Acceleration of all the small masses (particles, atoms, molecules) making up stellar objects gives rise to weak chaotic gravity waves (hypothetically; gravitons). i) Could these tend to cancel each other out (destructive interference)? (Due to the chaotic manner.) ii) Could such destructiveness decrease with time, as weak gravity waves spread out in space? So that, seemingly, something would be getting stronger for instance with increasing distance from the center of a galaxy. iii) Since gravity waves are related to acceleration of masses, and otherwise not "emitted" by masses in and of themselves, this would be a different effect than for instance predicted by MOND. I don't think this could explain "dark matter", but one could wonder if it could explain some deviations which otherwise seem to cling to even the best dark matter models.

[@JonBrase]

9:38 As far as I understand, what we're seeing here is just a confirmation of existing theoretical predictions (that gravity interacts with gravity), and the statement "QG is non-renormalizable" is basically equivalent to "gravity interacts with gravity and black holes are a prediction of GR", which basically means that, at the Planck scale, gravitons couple with infinite strength to Planck-mass black holes, which means that loop diagrams involving black holes are dominant contributors to any vertex involving a graviton, which means that gravity couples with infinite strength to *everything* at the Planck scale, which then destroys the predictive power of QG in exactly the situations where it actuary matters.

[@kindlin]

Ok, you had me in the first half, but then you went and jumped off a cliff.

[@FrancisFjordCupola]

@@kindlin yeah. Makes me wonder how many great initial hunches and thoughts get shot down every day by people jumping ot conclusions.

[@evanpenny348]

FH, whatever you are on I want some.

[@oldguyinstanton]

I think I understood that.

[@oldguyinstanton]

@@evanpenny348 I know, right?

[@theCodyReeder]

I wonder if putting a detector at the solar gravitational lense would result in a stronger signal. In other words will the suns gravity bend and focus gravity waves like it does light?

[@YunxiaoChu]

Hmm

[@TheSandkastenverbot]

Are you sure that interference neccessitates interaction between photons? Interference is a linear effect that also happens in a non-interacting theory. Photon-photon interactions would be a non-linear effect.

[@oldguyinstanton]

This is what I wrote above as a direct comment. Could it apply to what you are suggesting? "So wait... at 10:58 it shows the light being detected 2 seconds after the peak of the gravitational strain. The photons were slower by 2 seconds over 100 million lightyears. So, IF the speed of the photons is affected by all the matter they had to go through, how much of this delay was caused by: (1) spacial curvature as opposed to (2) actual collision and re-emission of the photon with a component of an atom of matter in its path. In other words, influence vs direct contact? This is, I think, important, as it might tell us something about the nature and size of the hypothetical graviton. For example, if a significant amount of the slowness of light is caused by actual collision and re-emission, then the explanation for the faster speed of that gravitational strain spike might be that the graviton is "that" much smaller than the photon, so it avoids collisions "that" much easier. From this ratio, it should be possible to calculate the size of the graviton. Or is all of the above speculation just so much gee-whiz pig-ignorant layman science BS?"

[@CMNunn]

^ That's right, interference is linear effect and doesn't require photon-photon interactions to explain in quantum optics. That point was a bit muddled in this video... But from what I understand, interference patterns in gravitational waves would still be a good place to investigate nonlinearities. I'm not even sure if nonlinearities prove that gravitons exist, but it would constrain a theory of quantum gravity that explains how they behave

[@danieljensen2626]

It does not, she kind of muddled that. Photons don't interact, and the interference of photons is linear. What she suggested with the gravity/optical correlation is that gravitational waves experience gravitational lensing, which does suggest interaction an non-linear interference.

[@martijnklijn2068]

@@oldguyinstanton The 2 second delay is explained more simply and happens at the event itself. The light coming of the collision needs a bit of time to escape. Relativity tells you that time inside a strong gravitational field moves slower then outside, stretching that very small initial delay to 2 seconds. So it does not need to happen somewhere underway. In fact the 2 second delay is what is expected if there is no further delay underway. Thats why scientists accept the 2 second delay as prove that the ligth waves and the gravitational waves made the exact same journey at the exact same speed.

[@objective_psychology]

Self-interaction is a property of fields, not particles

[@k8tina]

Go to 2:53 to avoid the Better Help promotion/ad. You're welcome 😊

[@Lukkystarxiii]

Please more videos of answering fan questions! So freaking cool!

[@stevenverhaegen8729]

Hey, Dr. Becky - I don't quite understand where the 2 sec difference between the gamma ray and gravitational wave signal comes from, if you say they travel the same path and speed?

[@whiterosesalchemist]

Waves from the merging, 2 sec pause til explosion after merge.

[@jmarvins]

like the above reply said, the waves are coming from the final moments of spinning-in before the objects collide, then the collision happens and within a few moments after makes the explosive light - the delay is what you expect because the light comes from after the gravitational waves are being produced by a small bit

[@murraymadness4674]

@@jmarvins ok, but 2 seconds is a massive amount of time when talking about these things isn't it?

[@user-Aaron-]

​@@murraymadness4674Considering how massive they are, I don't think it's unreasonable.

[@johannageisel5390]

@@murraymadness4674 We are talking about planet-sized objects, aren't we?

[@aresaurelian]

Assumptions are getting in the way here, cancelling each other out to nothing, or reinforcing each other to mega-assumptions. Thank you, Becky, for clearing things up.

[@williambrown9166]

I am enjoying the mavitas with which you talked about mavity. Fantastic!

[@quintuscrinis]

Mavity? All sounded a bit wobbly wobbly to me, don't know where it was picked up. Mind you Alonsee and all that.

[@melodyqueen6432]

I think she was having a stroke... somebody should call The Doctor

[@CritterKeeper01]

@@quintuscrinis * *twitches* * wibbly wobbly….alons-y…..you did that on purpose, didn't you?

[@pierreabbat6157]

This question came up when trying to decipher Lemnian: Is "mav" a numeral? Is Mavity anything like Macavity?

[@spacelem]

But Newton didn't name gravity, it was already a term in use! He changed its interpretation. (Sorry, I am being far too pedantic)

[@itsnicole11]

Currently reading your book ‘A brief history of black holes’. It’s very interesting. I don’t study Astrophysics right now but have always been interested in the subject and have considered studying it (Just no jobs in that field where I live, basically science jobs are very few here)

[@michaelsommers2356]

For these types of job, you have to go to where the jobs are.

[@Johnnycrystalblue]

I’ve actually thought about this. Never said anything about it. Glad you’re responding to the question. If one person thought it and said something thousands thought it but didn’t say anything. ❤

[@System.Error.]

for anyone interested related to this subject: check out the following 1. gravitational wave lensing (lensing potential and so on) 2. gersenshtein effect

[@ggentry5189]

Great question Larry!

[@tevatronlhc244]

wait a minute, light interferes but photons dont interact with each otther, but in higher order qed (lepton loop), what is in low energy regime very suppressed. i thought interference is especially a property of none interaction cause they passing through each other and adding linearily, interaction of wave particles disturbes interference. so what is it for gravitons. may be im completely wrong. than help me out

[@drdca8263]

I believe you are correct. Another comment making the same point as you, said that we have other *separate* reasons to believe that gravitons interact with gravitons. I personally don’t know what those reasons are. Though, I would imagine that the fact that gravitational waves are influenced by the curvature of spacetime (though, it would seem very weird if they weren’t!), that that would at least suggest that gravitons likely interact with gravitons? But that the waves interfere? No.

[@weldonanderson5124]

Trying to think this through; so gravitational "information", such as waves (or theoretical flat signal as well?) must travel through spacetime the same as light does. So if we see the light from a distant light source lensed by an intervening mass like a galaxy, the *gravity "signal"* associated with that light source should travel the same lensed path? It seems a little weird to me to try to imagine masses creating space time curvature affects the passage?/transmission? of other sources of spacetime. Not merely simple wave addition and subtraction, but wholesale lensing. If this were not true, the em images of distant lensed objects would become disassociated from their gravitational signals, right?

[@tevatronlhc244]

@@weldonanderson5124 im not talking about traveling on a curved spacetime background but that 2 waves traveling on it interacting with each other. interacting means for me, exchanging particles. photons do not (but in higher order qed), thats why the interfere linearily, do gravitions in the waves interact with each other by gravitons and how strong is this effect. hard to say without quantum gravitiy. but as for light, one can calculate interference pattern at least classically with art, and there is the question, linearly or not. not there is field.

[@orionx79]

Photons can interact with each under ideal lab conditions

[@martijnklijn2068]

Fermions and bosons. The probability waves are different like sinus and cosinus. This means the two fermions cannot co-exist in the same place, but two bosons can. Particles that form matter are all fermions (so far as we know, dark matter might be made of bosons and still have mass). Force carrying particles are bosons as far as we know to date. This means gravitons would be like fotons, bosons without mass. The fact that they travel at the speed of light already tells us gravity waves have to be massless. With mass they'd slow down considerably and we don't see that at all over 100's of millions of light years. This also tells us another thing, if gravitons are like fotons, then there must be a graviton spectrum, similar to a light spectrum. Another test for Becky id say.

[@divyajyoti1631]

Gravitational Wave (GW) physicist here. The inference that GWs can interfere with each other because they can get lensed the same way as EM waves is incorrect. Gravitational potential is not at the same order as GW. While GWs can interfere, the effect is extremely small compared to the actual amplitude of the wave.

[@timothykeech7394]

Unfortunately one of the main causes of mental difficulty is the inability to pay for such treatments.

[@nzuckman]

Not to mention they've got a record selling users' private medical info to advertisers

[@JKTCGMV13]

That’s definitely not the main _cause_

[@XellithUS]

@@JKTCGMV13They said ONE OF the main causes.

[@Linguae_Music]

@@JKTCGMV13 It's in the top 3, for sure!

[@Linguae_Music]

I don't go to therapy, psychedelics are cheaper and more effective muahahahahaha

[@nbahn]

If memory serves, Richard Feynman felt that physicists at universities should be compelled to teach at least *one* undergraduate course in order to answer "dumb" questions from undergraduate students so as to be compelled to consider physics questions from unorthodox perspectives. He thought that Einstein should have actively pursued other questions in physics; rather than the one issue that made him famous.

[@ilari90]

I hope there would be better way to visualize that in 3D environment, as the visualizations are almost always visualized as ripples on a pond, and not as how the waves would travel in 3D, as the visualizations are usually done in solar system scale and when the star is essentially affecting the system. Maybe using dots around the objects instead to show the effect than those waves on 2d plane.

[@R055LE.1]

It's sooooooo much harder to draw

[@Gin-toki]

My guess why that is, is due to most instancens only concerns the interaction of 2 to 3 objects and thus visualizing it as ripples on a pond is sufficient. Only if a 4th object gets introduced and one that is not coplanar with the three others, does it become more relevant to make a different kind of plot to see how the various objects interact/are affected by one another.

[@markfergerson2145]

We see in 2D basically from things that are not at very great differences in distance from us. How would you build a 3D display? How would you represent that adequately on a flat display screen until 3D displays become common? Notice that there have been and still are many companies trying to build 3D displays.

[@DrBecky]

You might like this video that goes through different ways of visualising GR and space curvature in 3D that are scientifically accurate (I like the bit at 09:43 best!) kzbin.info/www/bejne/raPamHygd7qMjMU

[@I_Don_t_want_a_handle]

Yes, I was going to query that. It seems, to a dunce like me, a little misleading to use a distorted plane when, in reality, the distortion would be in three ( or four?) dimensions. Doesn't gravity distort time?

[@eonasjohn]

Thank you for the video & the question.

[@billthomas7644]

Always heard the term destructive interference. Never heard the deconstructive interference version before.

[@michaelsommers2356]

It doesn't matter; It's just words.

[@therealpbristow]

@@michaelsommers2356 "deconstruction" implies prior construction, that is now being reversed; "destruction" implies only prior existence. It's a useful distinction in some situations, and therefore worth keeping the two words distinct. Since destructive interference can happen in cases where there hasn't yet been any constructive interference - i.e. in cases where the two waves have never previously met - I'd say the word "deconstructive" is not appropriate here.

[@dannydewario1550]

​@@michaelsommers2356Wtf do you mean "it's just words"?! Like what point are you even trying to make? 😂 Words in science have very specific definitions. Surprisingly, different words have different definitions. If you don't care about consistency in definitions, then I highly recommend staying out of every field of science.

[@michaelsommers2356]

@@dannydewario1550 My point is that words don't affect the physics, and the physics is what matters. If you can't figure out what 'deconstructive interference' means in this context, then you should stay out of every field of science, because you obviously don't have the intellectual machinery to understand and certainly not to do science.

[@Jericho6115]

You are awesome, Dr Becky. Your enthusiasm and energy is akin to Carl Sagan. Your voice and cadence is unmatched. Thank you.

[@qazsedcft2162]

One thing I don't understand is how do these supposed gravitons escape a black hole to affect the universe outside?

[@garethdean6382]

They don't. A black hole's properties are 'imprinted' on its horizon, held there by infinite time dilation. (This includes things like charge and spin.) The space around the hole can interact with things and this is what will emit gravitational waves. To the point that, when two black holes merge, the resulting hole is larger in volume than both combined and encloses a lot of nearby space, preventing even signals that originated outside the initial holes from escaping.

[@williammcguinness6664]

So it's a distortion in space that causes gravity waves ​@@garethdean6382

[@anthonybullard4441]

​@@garethdean6382 that's missing the point, though, isn't it? "Time dilation" is just the curvature of space-time. If curvature is caused by gravitons, then that curvature is caused by something that the curvature itself doesn't allow. It's a paradox. The gravitons cause a curvature which doesn't allow the gravitons to escape the singularity where the mass is, which means there's no curvature, which means the gravitons can escape causing a curvature which won't let them escape...

[@andrewthomas7109]

This question makes my head hurt, which means it's a great question!

[@k9876k]

@@anthonybullard4441 Yeah that's one of the main problems with trying to quantize gravity. With other quantized theories, those divergences/infinite interactions can be ruled out with renormalization but for gravity it doesn't work at all for the reason that you explained.

[@a11oge]

yet another of Dr Becky's videos that blow my mind.

[@silliconcarbon6637]

3:13 Don’t you mean bending SPACETIME, instead of bending “space”. I feel it is a significant difference, that’s often explained wrong and therefore often misunderstood by the general public.

[@galoomba5559]

Yep. Almost everyone uses the rubber sheet analogy but fails to mention that it's just an analogy and not what the curvature of spacetime actually looks like.

[@PublicRecordsGeek]

Space is stretched as Time is compressed and vice versa. Where time goes slower is "down," and the difference of rate from this to that region is a gravitational 'pull' magnitude. It's a consequence of Time moving at the rate of Causality even though the interaction is slight. Any difference from that absolute rate is a 'corner' in space. Some has mass, some has gas, some has enough of both to make the corner "bigger." Some corners have so far collected little mass, but none the less effect in bending space.

[@francom6230]

She is not concidering many of her assumptions are totally unproven ideas,, the kind w no proof.. ya kno?

[@metastatic746]

​@@galoomba5559that is because spacetime is 4d and therefore difficult for a lot of people to comprehend. I don't even know if I am understanding it correctly after watching videos/lectures about it for years, but my impression is the 3d version of the rubber sheet analogy would look like a planet dropped into spacetime that gets smaller as is shrinks and the fabric pulls away from your reference point. I personally think that a planet the size of earth dropped into spacetime 100 miles from an observer would become even further due to the stretching that happens. I don't know by how much. So, am I far from the truth? Please dissect this description if you have the time. I must know the truth.

[@glenwaldrop8166]

Pretty sure the time aspect being a variable is because of the compression of space caused by matter. You bend space and you alter how energy works in that space. Outside of a gravity field atomic decay accelerates as electrons are allowed to spin at greater distances.

[@Mysztek]

REMINDS ME OF HIGH SCHOOL WHEN HAVE TRICK QUESTION. No they can't interfere with each other. But they can compound on each other.

[@MrKago1]

Wow, what a question. Now I have so many questions. How would a gravitational interferometer would work? Can you double slit gravity waves? What would be the results? Do they reflect off of anything? Does mass act to gravity as a lens does to light? If you can double slit gravity waves, can we do an experiment similar to the one that showed you can affect the waves backward in time? If they stretch and compress space, and inside black holes space and time trade places, do they oscillate time?

[@benjaminbeard3736]

I did read somewhere, I can't remember where, that gravitational wave can be lensed. Because they are distortions of SpaceTime itself, yhey follow the contours of spacetime.

[@michaelsommers2356]

_"How would a gravitational interferometer would work? "_ Take a look at LIGO to see how it does, not would, work.

[@aarcaneorg]

Excellent question. Excellent video. A better question though, and perhaps more enlightening, would be "can gravitational waves interfere with themselves?"

[@takanara7]

You would need a way to bend gravitational waves the way you can with light. I guess gravitational waves can be lensed by more gravity - in which case you could have a gravitational wave that gets delayed by a gravitational lenses around some galaxy cluster and then appears to cancel itself out when the frequency is right.

[@rockapedra1130]

Why is there a delay at all in the arrival time of gravity waves and light? Light gets generated a full 2 seconds after the merger? That seems so counterintuitive! I would guess the light would start getting generated BEFORE the completion of the merger? Instead, it peaks 2 seconds AFTER?

[@tonywells6990]

Light interacts with matter as it passes through the exploding dense neutron star material, but gravity goes through matter without interacting so is not delayed.

[@JonBrase]

In supernovae, the peak is *days* after the initial event. There will be some light emitted at the time of collision, but as the material spreads out you'll see emission from more surface area and from deeper depths into the cloud of ejecta. You're also likely to see significant additional heating of the material after the collision from radioactive decay: neutrons aren't stable in vacuum but are at the pressures found at the center of a neutron star, so the ejecta will contain tons of isotopes that are way too neutron rich to stick around at zero pressure. The average half life of these isotopes may heavily influence when the event is brightest.

[@rockapedra1130]

@JonBrase Wow. That makes a ton of sense. Thanks, man!!!

[@rockapedra1130]

@tonywells6990 thanks,man!

[@JonBrase]

​@@rockapedra1130Also, in response to another comment, someone mentioned the possibility of equipment delays: i.e, the two detections were simultaneous but for technical reasons the gamma detection was reported a couple seconds late.

[@MemphiStig]

Fascinating discussion. I enjoy reading the comments section too. Lots of great discussions.

[@thebeber2546]

It always starts with a seemingly simple question. Great and very interesting video. I can‘t wait for some more measurements on gravitational waves.

[@PBeringer]

I just saw the title; this is something I've wondered about a lot! What happens at points of constructive and destructive interference is fun to consider - the nulls ... they're a bit scarier. Haha. The especially fun idea is that if they propagate conventionally, as any acoustic or electromagnetic wave, etc., they'd also be time-reversal invariant. The potential implications for THAT are even wilder (once we can generate them ourselves, that is).

[@doryiii]

Light slows down in a medium right? which is why we have refraction. Space is very empty but not completely empty; there are hydrogen atoms and plasma around which will very slightly refract any light. Light travelling through a large distance in space should have slowed down thanks to this. Doesn't this mean gravitational waves are also refracted the same way? which is very unlikely because even with light, refractive index differ for each frequency. Or can the 2s difference be explained by light refracting in space?

[@nirorbach8046]

First I solute you for explaining this subject at the edge of physics research to the general interested public in the most understandable way. Regarding the topic to the best of my personal understanding: Many years ago I was taught in my advanced Quantum Mechanics course that the static electromagnetic fields do not undergo quantization, but only the dynamical ones. If this is true also to gravity, it means that the observation that gravity waves follow the static gravitational field doesn't yet imply that they interfere with each other. So only if one sees a couple of gravitational waves simultaneously (or through a nonlinear effect of a single source as you mention), one can deduce the interference does occur. But we need much more sensitive detectors to see such a couple of gravitational waves, because they are much harder to detect than water waves or sound waves...

[@zooblestyx]

Please consider a different sponsor. This one has a pretty appalling data security record.

[@telling25]

This kind of melted my brain - thank you 🙂 The first reaction I had to the title was; yes of course. Gravitational waves are ripples in space time, so of course they can cause local gravitational lensing. After hearing the video and thinking a bit I have a couple of things I can not wrap my brain around. First, if the waves are strong enough, how would a lensing effect of another gravitational wave look like? And is it a thing at all? Second, in accelerators you use electromagnetic waves to accelerate particles. Essentially letting the wave ride on the electromagnetic slope. That got me thinking what effect wave riding a gravitational wave would have on photons? After all, they already are moving at the speed of light. Increase of energy? And would such an effect be visible in the burst of light that has been traveling along the gravitational wave for millions of years?

[@martijnklijn2068]

Such wave riding would look an increase in the energy of a foton. A blueshift.

[@telling25]

@@martijnklijn2068 Then, would it be possible to see the variations in energy shift as the gravitational wave passes us? There should be an variation of the photons emitted from the event as parts of them blue shifted and some are red shifted.

[@evanray8413]

Should be called DESTRUCTIVE interference.

[@nicolasblume1046]

10:40 I don't quite understand: Why does an interaction of different gravitational waves imply that there needs to be a graviton? Couldn't there be other explainations?

[@slabrankle9588]

If I discover the carrier particle for gravity I'm calling it the Gravioli. Don't try to talk me out of it.

[@alwaysdisputin9930]

After your discovery of the gravioli, priority number 1 is the development of gravy bombs.

[@therealpbristow]

You'd better hurry! There's thousands of ships being launched every day carrying detectors for those things... =:o}

[@slabrankle9588]

@@therealpbristow I'm working on it night and day and I believe I'm close to a breakthrough. Watch this space for further developments.

[@davidraiklen4521]

Kind of amazing that a more detailed study of relativity is possibly the way to quantize relativity. I'm so impressed by the work of the LIGO-Virgo team. It's really a new chapter in astronomy and physics. I heard Kip Thorne's first lectures on it at CalTech, and it became a lifelong passion, to understand and tell people about the development of this incredible telescope. Kip is an amazing, unforgettable speaker. Thank you for the beautifully clear explanation of one of the cosmic questions. A wave smaller than a proton has info on a far off black hole.

[@mawkernewek]

1:15 You're not just chatting about mental health, you pretend you want to chat about mental health and segway into an ad.

[@smenor]

and / worse an ad for Better Help which is a beyond horrible company

[@StuftBanana]

That’s what made it a good/conversational segue. 🥂🖖🏼

[@dannydewario1550]

I think Becky got confused at 8:38 There was a very clear time delay (of 2 seconds) between the gravitational wave peak and light wave peak. They were NOT detected at the same time (unless she's talking about some other piece of evidence she's not showing us). So that means the path light took was longer than the path the gravitational waves took. So this would actually be evidence against gravitational waves being affected in the same way as photons. Or in other words, gravitational waves aren't affected by other gravitational waves. Unless someone can explain to me what I missed, I think Becky made a mistake here.

[@yeroca]

Deconstructive →Destructive

[@watcherofwatchers]

You have failed in your attempt to be unnecessarily pedantic and correct an actual expert. Google your own statement.

[@yeroca]

@@watcherofwatchersYou have failed in your correction. I'm not saying deconstructive isn't a word. I'm saying it's not the traditional word used with wave interference. So I challenge you to google that. The two words are constructive and destructive.

[@carmattvidz4426]

Honestly, when contemplating the universe and the vastness of space, I believe I would be quite content aboard a spacecraft bound for Mars or the outer reaches of the solar system. Ice fishing on Europa (with adequate radiation shielding, of course) sounds incredibly appealing to me. The solitude, with no one to pester or disturb me, is something I find enticing. Some of us indeed thrive and yearn for isolation

[@brothermine2292]

It's called destructive interference, not deconstructive interference.

[@slabrankle9588]

The term "destructive" might hurt some feelings. Even grav waves have feelings these days.

[@raktoda707]

Thank you comprehensive overview

[@smenor]

Better Help ‽ Come tf on.

[@Dismythed]

The theory I have been exploring for several years now is that 1) the void of space is not a fabric (no fabric has ever been demonstrated, only the space between infinitesimal particles shrinks), 2) that other types of non-gravitational waves, like light waves, do NO WORK, but their particles do the work, but 3) gravitational waves do, in fact, DO WORK, but not because of gravitons, 4) but gravity is an existential effect of objects compressing (without wave) or stretching the distance between two infinitesimal particles whose default mode is to conserve the distance between them, 5) the gravity wave continues forever unless interfered with, 6) only particles can interfere with it, not other waves, gravity or otherwise, 7) because the delay by causality causes the two particles to change the distance between them as one of them moves, 8) the composite effect, therefore, is that gravity waves are generated when clumps of particles (large bodies) experience massive causal wave effects that travel outward, producing a wave in space. Now what this does, in regard to the theme of this video, is it does NOT allow gravity waves to grow larger or cancel out by contact with other waves. A gravity’s wave will ALWAYS be the same height as it moves out. It cannot get taller or shrink, until it comes in contact with a physical infinitesimal particle. Then that particle will absorb all the remaining energy of the wave of the particle that sent out that wave. However, this is a really small contribution, and smaller the further out it goes as per the inverse square law. So what happens in this scenario is that objects are affected by gravitational waves and multiple gravitational waves converging on an object will affect that object as if the waves interfere, but the gravity waves themselves will act like the other wave does not exist because they are just caused by one object attempting to conserve the distance between itself and another object. So any seeming measurement of interference is coming from physical objects. The 1.5 second delay between the wave and the light seems to indicate this. That both were constant indicates they followed separate paths. If true, this would be a fifth translation symmetry, generating the law of conservation of distance due to distance symmetry. It would be the holonomic non-quantum cause of relativity, causality (time), energy and gravity. Violations in this symmetry cause small effects that add up to large effects based on the intensity of the violation of distance between infinitesimal particles. So, then, what precisely is distance translation symmetry? It is that if there are only two objects in existence, they will seek equillibrium by remaining the same distance from each other, neither attracting nor repulsing. But by moving one, the other will seek to follow it to maintain the distance. Because of causality (time symmetry), reaction following temporally after action, movement (spatial and rotationsl translation symmetry) of infinitesimal particles causes gravity by constantly violating distance symmetry. It could also be stated that two infinitesimal particles in static equillibrium will have equal attraction and repulsion. When distance is violated by movement, the equilibrium of attraction and repulsion is also violated, generating specific gravity (attraction; +distance) and generalized universal expansion (repulsion; -distance). This is why I believe photons (the same photons we know and love) traveling out from stars and other light-producing phenomenon are the cause of universal expansion and that's okay because it is not uniform, allowing matter to flow in rivers throughout the universe and recollesce in empty regions. Thus, any void gets filled with collescing matter, allowing the universe to continue indefinitely.

[@willparker1404]

Better help is a predatory company. Stop allowing them to sponsor you for integrity’s sake.

[@blijebij]

It is a fascinating question! Splendid question from one of your guests.

[@rockapedra1130]

"deconstructive interference"? Is this a euphemism for "destructive interference"? 🤓

[@GuitaRN-David]

I love all of Dr. Becki’s videos

[@ClassicPass_]

Please give Lesser Hurt Their money back... you don't need that crap. 😢

[@Gin-toki]

If one thinks intuitively about it, but not in the sense of how waves behave but in the sense of an imagined space with two objects on the same line and equidistant from an observer in the center of the space. If the two objecst has the same mass the gravitational pull they have on the observer in the centre will be equal but opposite and thus cancel out. If now a third object with an mass is introduced next to either of the other two and on the same line, it will contribute to the gravitational pull on the observer in that direction, thus the gravitational pull is no longer cancelled out but instead increased in the direction of where the new object is placed. Any movement of the different objects relative to the observer will result in varying gravitational pull in different directions. The exact same thing happens when looking at how waves behave in water when something causes ripples in it, from eg a drop. So yeah, it would surprise me a lot if gravitational waves did not behave like any other wave, otherwise a namechange for it would perhaps have been in order to not cause confusion :P

[@TheNewSchmoo]

Thumb down and stopped watching at the sponsor spot. Go to them if you want all your problems etc sold on the open market.

[@JKTCGMV13]

They sponsor a ton of her videos so you might as well just unsubscribe instead of coming back just to dislike and stop watching

[@TheNewSchmoo]

@@JKTCGMV13 Hopefully the full story of their selling confidential information will hit the headlines soon.

[@Grungld3763]

I don’t think the promotion of therapy is a bad thing.

[@wayneosborne2506]

Just fast forward dude

[@smenor]

Hard same. Better Help is garbage. Had hoped Becky got better sponsors but nope. Pitiful.

[@linuxophile]

Interference as described is a linear phenomenon. GR is nonlinear, so definitely they interact not by superposition. OTOH, gravitational waves are also essentially linear phenomena when they reach us (they are result of perturbation theory, i.e. linearization of the GR equations). I.e. the answer I think is "of course there is interference for weak waves because their math is the linearization of a nonlinear equation". BTW if you want to see how nonlinear waves interact, see the pictures of waves in shallow water (KP equation).

[@SodiumWage]

I LOVE your channel, but I'm gonna have to stop watching your videos if you keep sponsoring the company in your ad. They are a scam, we all know they are a scam, and it's sad seeing this scam being peddled by one of the best science KZbinrs. Please, Dr Becky, do better.

[@FrankDijkstra]

I actually asked the same question a few months ago in the comments. Good to see more people thinking the same thing🙂

[@AndyGabrielPowell]

Learned so much about the universe from your videos Dr.Becky. Thank you.

[@AshishMishra-li7vd]

I watched a lot of your videos, and it seems like this one become my favourite. Very well explained. Thanks a lot 🙏

[@JimHelfer]

Fascinating...Therapy does Help.

[@JohannPetrak]

4:54 waves cancelling out is called "destructive interference" not "deconstructive interference" as mentioned and written in the video

[@dougrife8827]

One point not mentioned in the video is that GR itself is a nonlinear theory. In fact, if GR was linear, such as electromagnetic waves, the field equations of GR would be trivial to solve. They can be solved but only approximately using advanced numerical methods that need to run on a supercomputer. These numerical methods are one of the most important achievements in the study of gravitational waves. Without them it would not be possible to determine the masses of the black holes is a merger, for example.

[@gordonwallin2368]

Thank you, Dr. Becky. Cheers from the Pacific West Coast of Canada.

[@RussPanneton]

Love learning from and listening to your videos!

[@nicovandyk3856]

@Dr. Becky, two questions: 1. What is the amplitude of the gravitational waves close to the event itself? Is it strong enough to rip matter apart (I.e. the gradient of the stretch is so high that it is shorter than the electrostatic forces between atoms/molecules or even the strong force? Is that possible? Is that a potential reason for hypernovas?). 2. Can that gradient get so intense that it becomes shorter than the Planck length (Especially in the space between two supermassive black holes that is about to collide)?

[@stewiesaidthat]

Hypernova equals E=mc^2. The outer shell of the star accelerated the inner core causing a supermassive atomic bomb explosion. The laws of physics are equally applicable in all frames of reference. Just take the physics for an atomic bomb and apply it to a star collapse. Nature abhors a vacuum means an equalization of forces. Since Newton's F=ma -> F=a. The matter that is left over from the explosion rushes back in to fill the vacuum. If there is not enough acceleration, a 'black hole' is formed. Ie. A celestial object that doesn't have enough acceleration to produce electromagnetic waves in the visible light spectrum. In a rotating frame, the top/outer radius has more acceleration than the bottom/inner radius. The top falls back into the bottom. That's how you get 'star collapse'. As for planc length. How many times can you cut something in half? Infinitesimal. In nature, what is the smallest possible wavelength? Using E=mc^2 where mass decreases with Acceleration and E=a, taking all of the energy contained in the universe and accelerating it all at once, that should result in the shortest possible wavelength. Factor in the fact that the universe has an infinite amount of energy, there is no limit on how small a wavelength can be. That's demonstrated by Pi. That's why modern physics is stuck in a rut. E=mc. Acceleration defines mass. What defines Acceleration? Acceleration defines itself = Infinity = Religion. Becky won't admit this but that's where the real science leads you. Energy can be neither created nor destroyed, only transformed. E=mc -> E=a or Everything comes from Acceleration. And Acceleration is infinite as in the universe is unbounded, no limits. We just happen to exist in a region of the universe where energy has transformed itself into intelligent life. That's why modern science is still playing in the flat earth/science denial sandbox.

[@dichebach]

If you have not read it before, check out "The Structure of Scientific Revolutions" by Thomas S. Kuhn. In this influential work, Kuhn introduces the concept of "paradigm shifts" in the history of science. He describes how scientific communities operate within dominant paradigms or frameworks during "normal science," where researchers work within established theories and methodologies. However, Kuhn also discusses "revolutionary science," where new paradigms emerge, often through periods of crisis or anomalies challenging the existing framework. These shifts mark major changes in scientific understanding and practice.

[@DerekJones1081962]

Great explanation! I definitely wish that I could make time to study this science in greater detail. I'm still playing catch up for not studying astronomy earlier in my life.

[@brianlebreton7011]

Love your explanations. Thank you!

[@ozzy6162]

Here's a few more (possibly daft) questions Becky...... (1) Is there any concrete reasons (i.e. results) that show that space-time should (or possibly shouldn't) have a quantum nature? (2) How confident can we be in modelling the non-linear effects of interacting gravitons in such extreme conditions (mergers) when quantum mechanics isn't fully understood? (3) KAGRA in Japan is the 3rd gravitational wave detector. Are there plans to have detectors on every continent?

[@VGAstudent]

I reimagined your quantum gravity question on the reverse side and asked myself; "What if we can't see intermediate black holes, because their size is exactly the same size as a gravitational wave?" so they become a part of space as we see it with NO gravitational effects on things at all, because it becomes dark matter that is literally out of phase with our spacetime? We'd have to see a merger of two smaller black holes that cancel out, as evidence, ironically.

[@Chem0_oPoet]

Mavity? 😳 MAVITY! 🙀 We have a fellow Whoian!! 😂😂❤ I absolutely love your honesty, and the personal touch that your bloopers bring to your channel. It feels like having a casual discussion with my favourite mentor, instead of a stuffy lecture where you just "shut-up and listen". Thank you for being awesome!! 😸

[@DrBecky]

Thanks! Glad you enjoyed it :)

[@backwashjoe7864]

Mavitons!!

[@gregoryknowlton3734]

i have two questions 1st what happens to gravity of the star when the star goes supernova, does the pressure wave push the planets off into space? Would that be considered dark energy My 2nd question is if you had six Hubble telescopes around a Black hole at a safe distance, Put them at coordinates (x,-x) (y,-y) (z,-z) lets say Six light years away from Black Hole for each point. what would each telescope see? thank you for all the cool stuff you answer.

[@brandyballoon]

Perhaps a better question, one that would lead more directly to the answer, is how would it be possible for gravitational waves to not interfere with each other?

[@mikebartling7920]

Spot-on, thank you for your informative and fascinating talk. I look forward to your future videos.

[@JammyThoson]

My hypothesis prior to this video was that both gravity and gravitational waves distort spacetime, and therefore from a "mechanical" standpoint should interfere - in spacetime as a field. This would not evidentiate particles of gravity being able to interact amongst themselves.

[@s1gne]

I'm starting to wonder now. If light has frequencies and each frequency is a different color or type of light (some visible, some not), wouldn't that imply that if gravity could have frequencies and thus have different forms of gravity aswell? If gravity is a type of particle with a wave function anwyways.

[@babyoda1973]

Thats my question and all the implications

[@JohnHowshall]

I really loved this video- it’s my favorite topic! Though I’m one who is skeptical of the elusive graviton I agree wholeheartedly that gravitational waves interact with each other.

[@tfl-larsm24]

Thanks for a really interesting question discussion, particularly as an ol' geophysicist writing my first paper on Earth gravity, or rather how to detect fault zones with gravimeters. But, listening to this episode, I hit me: The gravity observatories work on long-distance objects, likely exhibiting some form of frequency "redshift", forcing Ligo/Virgo/Kagra to have these long receiver antennas. But how about our own solar system? Jupiter does affect the Sun, displacing the point of rotation substantially, with the other planets to a lesser extent. It is not on par with two multi-solar masses, but they are very close and we know their position to a few km at any point of time. So, why isn't it possible to measure the solar systems' far better-known entities' gravimetric influence to work out better theories? Ligo/Virgo/KAGRA have sensitivities far above a modern gravimeter, and in my time, we did see fault zones and ore bodies without problems. The antennas might need to be tweaked for "shorter" frequencies than remote neutron stars, but making a gravimetric model of the solar system with solutions for different upcoming planet positions might make detection possible.

[@EL_DUDERIN0]

Hey Dr. Becky: since light is affected by gravity as it travels to us on Earth from vast distance-- could this explain redshift in lieu of dark energy?

[@GraniteStateColin]

Dr. Becky, even though gravity interacts with gravity (a great proof you provide based on this observation!), that does not mean that gravitons (if they exist) can collide. Gravitons, as currently theorized, would be spin 2 bosons. Bosons, like the definitely-existing spin 1 photon, can occupy the same space as each other and so cannot "bounce" off one another. On the other hand, this same property might mean that it's possible to create interference patterns of gravity like with photos, which would be a gravitonic hologram. Cool.

[@TheGigashadow]

Love the channel! Just a word of warning, BetterHelp are starting to show signs of possibly being a bad organization. It's almost an Established Titles type scenario from the early investigations, so maybe beware of them at least until more is known!

[@wrekced]

@DrBecky What about that 2 second delay between the gravitational wave detection and the arrival of the light? Doesn't that indicate that the gravitational waves are less affected by the intervening sources of gravitational interference?

[@DavidKnowles0]

Others have said that the delay is accounted for at source, the gravity waves are emitted before the light wave. We probably need more of a sample size to confirm this through.

[@johnwickfromfortnite5744]

As far as pure GR is concerned: In the weak field approximation, gravitational waves are a linear phenomenon, and they can add up/interfere/cancel like light in that theory. without demanding weak field / linearized gravity, the einstein field equations are nonlinear in the metric (the tensor describing GWs) and they are therefore self-interacting, but only weakly in most cases. light is purely linear, as their tensor, the 4 potential of electrodynamics, only goes into light's wave equation in linear order. water waves are only linear in the limit where the water is much deeper than the wave's amplitude, for insance

[@davidramos5559]

your videos always get me so excited for the knowledge that us humans are achieving! Like we are doing some insaaaaane things! It's so cool! THANK YOU for making this wonder accessible to us folk who haven't formally studied in these fields.

[@sholinwright2229]

Fantastic! Love this type of content.

[@kevinreardon2558]

Gravitons and photons are not particles or waves, but are both and we don't have the mathematics to deal with that. We are dealing with 200 year old concepts where they only knew about billiard balls and rivers. We have expanded well past those models and need to consider different ones. We have the mathematical skills to do that. Photons and gravitational waves are properties of space and how space transfers energy through it. The fact that gravitational waves and light waves coincide, highly suggests this.

[@Max..Q]

Now I'm wondering, if there are gravitational freak waves out there like those 20m + water waves occasionally plowing the oceans? And if so, how "high" can those waves get? Can they become so strong that they rip matter apart? What are the probabilities of the occurrence? Am I on the way to unlock a new phobia?

[@voidagent]

It should be remembered, when Einstein theorized about gravity waves, he didn't think they would ever be detectable. Also, he gave a lecture in Switzerland in German about the Ether and General Relativity that doesn't seem to be well read in the physics community. These are not gravitation waves, the theoretical wave between two masses, they are gravity waves produced by a mass moving in the void of Space-Time. A pond is a 2D analogy of a 3D volume but two neutron stars coming together produces a "click" as they stick to each other. It like throwing a rock into a pond and that is the analogy Einstein used in his "clarifying" lecture, calling the Space-Time between stars, the Ether.

[@BenTrem42]

Good question. Like _"How come people warp truth, manipulate others, evade their truths, and expect happiniess?"_ *BUT* ... he also asked about collisions. So, honestly, wasn't that just word soup? Who, I ask ... who would think that waves would "collide"? Terms have weight.