3. The Doppler Effect and Special Relativity

MIT 8.286 The Early Universe, Fall 2013
View the complete course: ocw.mit.edu/8-286F13
Instructor: Alan Guth
In this lecture, the professor discussed the doppler effect, time dilation, Lorentz-Fitzgerald contraction and relativity of simultaneity.
License: Creative Commons BY-NC-SA
More information at ocw.mit.edu/terms
More courses at ocw.mit.edu

[@gnasty30]

These videos are a gift and I thank for them

[@FelipeBl100]

I like the very simple example in around 30:00 about time dilation and light arriving to an observer in a different frame of reference than of the source. Very clarifying

[@ericsu4667]

Time dilation is not real. It is purely mathematics from Lorentz Transformation. vixra.org/abs/1704.0187

[@luisgeniole369]

Here's a completely non-controversial discussion: Don't you guys think that the intuition with which Einstein arrived at Relativity, that of physics not being so "sloppy", could be extrapolated to our current speculations of what lies beyond the standard model? I mean, the ether of classical mechanics and the 10^272000 metastable states both feel like way outs, like patches on a designer's dress: they're pretty much unverifiable with our current technology and they heavily imply that the laws of physics aren't universal.

[@mg-il6km]

Great lecture. Very clear and to the point. Thank you!

[@mubarakhussain6462]

Its a profound lecture by one of the greatest contemporary minds.

[@macieyid]

This lecture is a treasure. The example presented during the first 20 minutes is how every introduction to relativity should look like. If, like me, you're still not clear on how the non-intuitive stuff about photons fits together, watch this.

[@4567mariusz]

So amusing watching this genius perform elementary algebraic operations on the blackboard. I'm grateful to MIT for making Alan's lectures available online.

[@ericsu4667]

Doppler Effect is a good example of variable speed of light in various inertial reference frame. For example, a person moving toward a microwave oven will detect higher frequency in microwave from oven. However, microwave forms standing wave inside oven. Therefore, two microwave of same wavelength but different frequency. vixra.org/abs/1705.0324

[@alias40anon]

It is a complicated by interesting subject. A great and suitable for the job professor by the way with a deep theoretical understanding

[@brainstormingsharing1309]

Absolutely well done and definitely keep it up!!! 👍👍👍👍👍

[@adurgh]

The only sticking point for me was the discussion about accelerating clocks. The effect of time dilation has to do with the time dimension as measured by any means, and a particular clock design is irrelevant, so the physical effects of acceleration on an actual clock being the motivation to introduce the concept of "ideal clock" seems unnecessary; even confusing to me.

[@CrownOfGoldCompleatSacrifice_2]

System progressing two failed attempts at going back to the things before. On different note. At the end of last month I felt great and was ready to progress

[@laszlogmeszaros3046]

Hywel 4 is correct. Someone is finally out there, who is willing to think. It's great.

[@ShubhamBhushanCC]

The dude who asked the Galilean Relativity question is a genius. I never thought of it but now when I worked it out, it blew my mind. Damn!!! Physics is beautiful

[@aphysique]

What do you think of Non locality of consciousness? If you have any thoughts on that particular subject matter? Also since you seem to understand thing's well, do you have a hypothesis on or about how or why Quantum Entanglement or spooky action at a distance work's? I'm just throwing questions at you sorry!🤔

[@luisgeniole369]

@Esoteric Fitness that's one mighty comfortable armchair you must be sitting on, may I ask where'd you buy it?

[@louerleseigneur4532]

thanks mit

[@CrownOfGoldCompleatSacrifice_2]

It appears we may not be getting it but as our thoughts change and it takes time to get to full understanding, they are past your life cycles so the change is instant

[@philoso377]

Page 24:00 regarding Aether. Albert Michelson and Albert Einstein didn’t (know or scrutinize) enough of the principle of operation in the apparatus employ in light speed measurement which is “incapable” of determining presence of Aether or not, consequently declare that Aether do not exist ... by ignorance.

[@owen7185]

his lectures are very good

[@richardsmith6488]

Did he state the clock difference equation incorrectly at time 1:07:27, when he talks about simultaneity. He seems to state the clock difference is βLC, and it should be βL/C. The term is shown correctly in the slide.

[@davidwilkie9551]

In the Quantum universe, the observation by resonance is equivalent to the emitted pulse and return of radar, so the "pinged" clock would show a normal rate of elapsed time at a higher or lower reflected frequency, and if it's travelling at relativistic speed then you probably can't detect it at a reasonable temperature, approximately as with black holes and orbiting light emitters? The equivalence of EM and reciprocal mass is balanced at the ground-state of spacetime resonance that is interpreted as distance, velocity and acceleration combinations of orbital in frequency multiples and bands. The observable event is a comparison of time-rate/timing, harmonics and period duration-history, ..comparing those different combinations of the universal clock-time superimposed ratios perceived as spacetime coordinates. ----- Einsteinian relative-timing ratio-rates analysis of the positioning.., of Violin String vibrational chord structure between the bridge and nut.., you, a Violinist of reasonable ability, can hear and identify Red-Blue shape shifting relative-timing ratio-rates when sliding the emissions of the Bow along to and from where the receiver-fingerboard is connected to the body of the Instrument. It's an example of Galileo's Musical Mathematical Measurement Methodologies in continuity.

[@saritchauhan8208]

Why delta time prime( ∆t’ as he pronounced) can't be equal to delta time sub source (∆ts) when both are in same inertial frame for moving observer case. He himself says that stationary source and the screen(or we) are both in same inertial reference frame when asked by a girl at 46:08

[@AnmolBauriya]

it can be equal if relativelocity = 0

[@manish__kumar]

What effect on the length of rod when it moving with velocity(v) in incline way (note : not is horizontal or vertical) rod moving in downward or upward direction... is its length change or no any effect shown.

[@sscheinfe]

he has the most elegant chalk handwriting I have ever seen. just sayin.

[@luisgeniole369]

I hate chalk

[@allanlees299]

The third aspect of Special Relativity, as illustrated in his viewgraph, seems to be wrong. The illustration shows the trailing clock as being in advance of the leading clock rather than (as it ought to be) behind the leading clock. So listen to the explanation and ignore the illustration for this element of the lecture, which occurs at 1.07.20 to 1.07.45.

[@suryapratapfire5383]

definetly but his statement in regard was correct listen carefully

[@zack_120]

25:44- I thought the heart of this section is the derivation of the dilation factor gamma. Then all the remainder is just obvious.

[@jaskirankaur8813]

Is there any relationship between non-relativistic and relativistic Doppler effect?

[@DrDeuteron]

The answer can be yes, maybe, or no, depending on how you look it at. *Yes* : if you track crests and troughs a la Doppler and add Lorentz contraction and Time Dilation. *Maybe* : if you consider the (relativistic) Doppler effect as a manifestation of the (lack of) stationary Aether. *No* : if you consider the RDE as the effect caused by they fact that the 4-momentum transfer of photons to/from emitters/detectors must be orthogonal to the emitter/detector's 4-momentum. (As it must be to maintain E = mc^2 after emission/detection). That math gives you the relativistic doppler with recoil included (due to light carrying energy and momentum).

[@wordysmithsonism8767]

Can a "uniform velocity" exist?

[@lingarajpatnaik391]

A Conceptual Error in the Calculation of Length Contraction in Special Relativity kzbin.info/www/bejne/n2LQnauiq8-Uiqc In matrix form the system of equations (5) is: L = γ γv L’ T = γv γ T’ (7) We verify that L’2 + (iT’)2 = L2 + (iT)2 . This satisfies the first cardinal principle. On inverting the matrix equation we receive L’ = γ (-)γv L T’ = (-)γv γ T (8) This corresponds to the system of equations (6) . These are the correct equations. Particularly, L = γ(L' + vT') (correct) . L = γL' (wrong). The conceptual error here consists in treating γ(vT') erroneously as being identically equal to zero. Consider, for example, in a given equation: A = B + C , the term C [here γ(vT')] is not identically zero. If we remove this term C from the equation, an inequality: A ≠ B will result, not another equation.

[@ericsu4667]

Special Relativity is wrong because it is based on Lorentz Transformation which violates the conservation of simultaneity. Special Relativity is correct in mathematics but wrong in physics. vixra.org/abs/1706.0498

[@JoaoVictor-qw4yl]

One question, applying the logic used at about 1:08:30 to the twins paradox, woundn't it suggest that in the twins paradox, it wouldn't make much sense that one twin becomes older than the older after the trip? (the idea that each one will read a slower time for the other)

[@yasserm.abdalkader2786]

No , the symmetry is broken here . to compare the clocks one should CHANGE velocity so it goes under an acceleration so the observer can't claim to be in an inertial frame of reference .

[@mohamedbarzaq7787]

Doppler effect and all written or said about relativistic Doppler effect is just science fiction and hallucinations .. I mean that Einstein's principle of relativity is wrong and impossible and all Einstein's thought experimentsare just creative false imaginations not more. see my article "DOPPLER EFFECT, A THIRD BEAM OR CAVE OF ALI Doppler effect is in total contradiction with Einstein's principle of relativity where the light imagined by Einstein don't change from at rest or in motion and its front beam don't retract , rear beam don't dilate and its vetical beam don't inclines contrary to real light experienced in Doppler effect and all written or said about relativistic Doppler effect is just science fiction and hallucinations .. I mean that Einstein's principle of relativity is wrong and impossible and all Einstein's thought experimentsare just creative false imaginations not more. see my p Doppler facebook.com/astronomicalbarzaq/posts/668832373278700 attachment 1-2

[@yasserm.abdalkader2786]

Have you ever studied relativity before ?

[@yasserm.abdalkader2786]

I even doubt that you EVER studied physics at a university level

[@swayamjha3988]

@@yasserm.abdalkader2786 even if he has had studied at even highschool level as I did he would known what he said is rubbish. 😂😂🤦🤦

[@garyraab9132]

1:16 Reading out the character symbols, while developing an equation, is not a sound educational practice... especially when the process includes a mistake in the character symbols (u) while developing the concept. The symbols used in chemistry physics and mathematical textbooks varies and overlaps incredibly. Better to talk through the conceptual meaning, while printing out the symbols representing the concept in mathematical form... I do not need to be told aloud that a letter ‘t’ is t! Taught physics for 34 years. Brilliant professors have not done their homework on the neuropsychology of learning.

[@edwardgalliano9247]

The answer is obvious. We are in Euclidean space inside an elliptic plane. It's just light is red-shifted by elliptic gravity.

[@Power321ify]

Things being said between 46:56 - 47:09 is wrong. The equation implies exactly the opposite of what's being said...

*) This is very strange, we are the observer but for us the time would not be Tobs but another T'. Three T in this derivation are confusing. In this case, because T' is our time, why at the end isn't it T' function of Tsource ? **) And on the first part what is being said between 40:33 - 41:33 is also strange with the extra distance including gamma

[@AnmolBauriya]

derivation of time dilation formulae were wrong delta t is always lgreater than delta t not

[@CrownOfGoldCompleatSacrifice_2]

It’s why they believe the words I am saying because that is what’s happening

[@HimanshuSharma-xn6uc]

For which year this lecture for

[@mitocw]

This was recorded in 2013. See ocw.mit.edu/8-286F13 for more info. Best wishes on your studies!

[@Fransamsterdam]

If you think the theory of relativity is wrong, the only thing you don't have to prove anymore is that you don't understand it.

[@ericsu4667]

On the contrary, Special Relativity is wrong because it is based on Lorentz Transformation which violates the conservation of simultaneity. Special Relativity is correct in mathematics but wrong in physics. vixra.org/abs/1706.0498

[@gyse6920]

Eric Su unfortunately you are incorrect. Einstein may have used some inspiration guidance and ideas but these are two totally different things. Special relativity accounts for parts that Lorenzt transformation cannot account for basically. It sounds like you read a link one time and drew a conclusion.

[@ericsu4667]

What exactly I am incorrect about? Be specific.

[@gyse6920]

Eric Su Lorentz transformation is the transformation rule under which all four-vectors and tensors containing physical quantities transform and that is all. A postulate is an (usually fundamental) assumption a writer makes in order to discuss a subject in a coherent fashion. Examples of postulates are the Born rule in quantum mechanics (which defines how the wave function is to be interpreted), or in classical mechanics the existence of a Lagrangian (which defines the starting point of theoretical mechanics). A principle is a more or less universally observed (usually fundamental) fact. Examples of principles are the second law of thermodynamics (universal dissipation), the principle of relativity (independence of the reference frame), or Heisenberg's uncertainty relation. A hypothesis is a theoretical assumption made to develop a (usually alternative) theory. Examples are Planck's and Einstein's hypothesis of quantized light, or the existence of supersymmetry. One can turn a principle or hypothesis into a postulate, but not a postulate into a principle. Note that it is possible that a principle is derived from a set of postulates. This reflects the fact that there is is some freedom in setting up the foundations. For example, the second law of thermodynamics can be derived from statistical mechnaics, and the principle of relativity can be derived from the postulate of Lorentz invariance.

[@ericsu4667]

OK. You know some physics but still did not answer my question. Specifically, why am I incorrect? Here are two papers for your reference. This paper proves that Lorentz Transformation is invalid in physics. vixra.org/abs/1711.0354 This paper proves that speed of microwave depends on reference frame. vixra.org/abs/1712.0130 My question to you again. Why am I incorrect? Please be specific since you know about physics.

[@krzysztofciuba271]

at 31:15nn a very smart question by a student and a typical v.bad answer - a typical in textbooks but the lecturer and textbooks do not recognize that the (Einstein-Langevin) light clock is only a model and not real physical clock; consequently, "time dilation" is a numerical measuring event (concerning the readings of stationary synchronized clocks) but not as a physical slowing down of "moving" clock (so called "moving clock attached to a moving object"). Consequently, the now 110years of interpretation idiocy about younger Twin (in "traveling") comparing to a "stationary" one. Relativity T. is a theory of field and not mechanical points and rigid mechanisms and rulers (that of Newton)!

[@chriskennedy2846]

Some of his statements about acceleration not having additional effects - if you take a series of instantaneous velocities, is in direct contradiction with Einstein's own 1918 paradox resolution which was later expanded upon mathematically by Max Born. I did a whole video on how a theory that is supposedly iron clad with consensus on how it all works is in reality all over the place and without consensus in the mainstream physics community.

[@krzysztofciuba271]

@@chriskennedy2846 Why do you need an "emergent time"? Time - on the definition (of Aristotle)- is a measure of change!! All experiments really are confirmation of GR and none of SP though mathematically on the principle of equivalence they are equal (centrifugal acceleration equals that of gravitational- R.Schlegel writes about it and easy to check it). Only as I know M.SAchs tried to present correctly the problem but he himself I think did not see the "tricks" of Tolman and C.Moeller (A.E in 1918 without maths and later Born) with "acceleration" period- hm, GR is base on equivalence principle but in the calculation, they..forgot about it. Why does?Einstein write about the "peculiar" effect though few lines earlier ..about the symmetry of the situation in 1905 article? He ..contradicts himself and he died without knowing the v.simple resolution (he preferred the mentioned 3 clocks that is just a hidden "acceleration period". Generally, physiscisst are ...methodological/phil. ignorant.You seem also talk as of..any clock (rigid body!) and forgot about the model background of the Theory: that of field!

[@chriskennedy2846]

@@krzysztofciuba271 If GPS clocks disprove the claim of symmetrical (or reciprocal of you like) time dilation, which they clearly do -then our perception of time comes from the rate at which particles and fields express their fundamental behaviors locally. This means every atom is its own clock. Then the question becomes: what is actually causing the slowing of their "clocks" as they experience stronger gravity or faster velocity? Einstein never proposed a mechanism. As a result the best we could do is accept time dilation as a co-effect of relative velocity. A couple of realistic possibilities are: 1) the relationship between a moving particle and its own surrounding fields is altered during increased velocity and gravity - and therefore the rate at which their local repetitive behaviors are expressed is impaired (slowed). 2) Velocity and gravity are altering other background field(s) that all of the local atomic clocks are swimming in and impairing behaviors that way.

[@krzysztofciuba271]

@@chriskennedy2846 GPS dissaprove??? A typical gravitation potential effect on the frequency of electromgt. wave (or "particle"!

[@chriskennedy2846]

@@krzysztofciuba271 no, disprove. I don't disapprove of GPS, in fact I couldn't get around without it. The GPS system as a whole validates many parts of relativity such as clock rate slowing in stronger gravity and with increased velocity. But the system disproves the claim of symmetrical time dilation as observed by the other. The GPS system as a whole needs to be in sync (very accurately) and couldn't possibly achieve being in sync if these clocks that are in relative motion each see the other's as going at a slower rate. If you adjust one side to compensate the other side falls out of sync even more. Work it out - you'll see.

[@briandoublas]

If something does not experience time, then it cannot change. If it cannot change, then its energy (wavelength, frequency) cannot change. A photon, 'moving' at the 'speed of light', does not experience time. So how can a 'moving' photon ever be red-shifted?

[@HimanshuSingh-jn1tf]

I doesn't, but it changes with respect to the observer.

[@mikegale9757]

That's an easy one. A photon is essentially a standing wave in time. You are moving through time. The photon is not. It's like driving over speed bumps in a parking lot. The frequency at which you experience the bumps depends on your angle of attack.

[@zack_120]

27:58-??? 😇

[@oscarobioha595]

I've gone through the comments, and only a few actually sound like physics students

To know why this derivation is NOT logical, see the second part of this video: kzbin.info/www/bejne/eHvcfKCOnqeImM0

[@laszlogmeszaros3046]

Dear IntegralMoon, try to get relaxed, take your time and start thinking. There is a great Hungarian saying: all flies love horseshit, but it does not mean that horseshit is good for you...

[@peterlue1156]

The aether experiments were done on earth. The Hafle Keating experiment has shown that time dialations on earth are frame dependant and if there is an aether it is in motion with the earth. This is in contradiction to special relativity. As for cosmic inflation, how is it possible that the universe is expanding but the average distance between galaxies is constant no matter how far we look back in time? Also a flat universe contradicts General Relativity unless the universe is extremely large and only locally flat.

[@peterlue1156]

The frame dependence of special relativity may be considered as evidence the existence of the luminiferous aether and proof that special relativity is incorrect. Frame dependence is not a feature of special relativity. If you assume that the time dependence was caused by general relativistic effects then we could only use the moments of acceleration to determine time dilations. I wonder how GPS satellites work in that case since they are in a non-accelerating frame of reference? If it is a combination of both, then more work needs to be done but occam's razor tells me that there is an aether since it explains everything classically and things that GR SR and QM cannot explain. Also the redshift tells us exactly how fast the universe is expanding. If we assume the universe is infinitely large and infinitely old then I guess we are back to the same problem as before.

[@peterlue1156]

We would expect to only see a constant c locally if the "fabric of space" is expanding. Because distant objects are not blurred as they pass through the gravitational fields of matter, we can assume that the speed of light is constant everywhere so the expansion of the "fabric of space" theory must be wrong. (The expansion rate is so high it should be clearly obvious) It will be a little tricky to prove because of gravitational lensing. But, the discrepancy between the expected speed and the amount of lensing when compared between stars of different distances away should be sufficient to accomplish it. (The discrepancy between the speed of light in regions where we cannot detect particles moving apart and regions where we can should be observable)

[@NouraElsadany--]

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[@stevenunua2118]

Well shit...if it in on the black board it must be true!!! LOL

[@hywel4605]

it is so obvious that the doppler effect in light actually proves relativity to be wrong. if relativty was correct you would have doppler in sound and not in the case of elec mag radiation. in sound it exits only because the emitter is accelerating to the wave. the observer is irrelevant. if you circle a swimming pool all the waves in the pool don't change unless you get in the pool and physically affect the wave - you have to come into conatct with the wave to make an affect. don't be dupped by this relativity nonsense.

[@IntegralMoon]

hywel jones I think you may need to review the difference between velocity and acceleration. You don't need to be accelerating at all to observe a doppler effect. Relativity is sound if you actually try to understand it.

[@hywel4605]

yes, i meant velocity in the case of a light wave; it is sound you can accelerate to. but the fact there is a doppler effect with light shows a weakness in the theory of SR. the observer is irrelevant as proved in water waves. believe me i have i tried to understand relativity, and i don't belive it at all. none of it! please have a look at this link. thanks for your comment. debunkingrelativity.com/ by Dr Srinivasa Rao Gonuguntla

[@ernestschoenmakers8181]

Hywel 4 I don't think you understand how relativity works but it is true, experiments have proven it.

[@DrJones-cs6qr]

+Hywel 4 Pseudo intellectualism at it's finest.Your conspiratard site doesn't prove shit btw.

[@hywel4605]

it is not my site. why does it not prove anything? you haven't actually said anything.

[@storaman12]

He cant write to the blackboard from the written notes; years and years teaching and still cant memorise a few notes and formulas. TERRIBLE. How come he is a lecturer in MIT. Go to university Yale and listen Prof. Ramamurti Shankar. How a lecturing same subject.

[@Prometheus4096]

Because he is superfamous for his research. MIT does research, teaching comes second. People go there to work with people who worked with Guth.

[@mousedorff453]

+Serhat Toraman It's much better to carry those notes though. Professor Shankar doesn't use notes because, really, a lot of the stuff he teaches in the course is very trivial. I mean, he doesn't need to remember the formulae cos he can just derive them from first principles in the class itself, hence the lack of notes. In this case, inflation is way more complicated and so, it would be best to carry notes and refer to them for formulas. It prevents confusion of any sort.