Do We Need General Relativity To Solve The Twin Paradox? 

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SR doesn't say anything about acceleration. Each observer is given identical clocks and measuring rods. One moves at constant velocity, the other doesn't. In SR it doesn't matter who is A and who is B. They both measure the same values within their respective inertial frames, for example, they measure the same value for the speed of light. Time dilation and length contraction falls from a comparison of A to B or B to A. Without the comparison there is no time dilation nor length contraction. Both will experience time dilation and length contraction depending on the point of view. A says B is moving. But B says A is moving. Swap your perspective and you get the same answers. The twin paradox arises because we compare the twins (thru observation of clocks) and say one is older than the other (time dilation). We define a point of view and define 'who' is 'moving'. We interpret that time dilation to be persistent once both twins return to the same inertial frame. Is it real? Perhaps neutrino decay is the best evidence for this? But, isn't there a larger concern here? If it is real, then can't we claim there is a preferred inertial frame. Wouldn't such a preferred inertial frame justify the ether? Wouldn't an ether change physics completely? Suppose that the ether could be explained as a series of coupled mechanical pendula. Special Relativity Hidden in a Series of Coupled Mechanical Pendula ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-e7nA5y497U4.html

For everyone who keeps saying that "we don't know the one-way speed of light" as someone kind of "gotcha!" (as if it actually matters in this case at all) (and, as if the Compton Edge Experiment hasn't measured the speed of light to be isotropic to within one part in 10⁻¹⁴) (and, you know, Maxwell's Equations, etc.) ​Here's a really good argument that the speed of light would violate the conservation of energy if it did not propagate at the same velocity in all directions: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-tVm2Cvy6UEY.html

So when I think about measurements in internal frames and use the verb "see", I never think about light reaching the observer. I think about his infinite lattice of graduate students with synchronized clocks and calibrated rulers, and "see" means what does the grad student who is at the distant event "now", at the time of seeing, measure. Right before turn around, the space twins grad student (bob) sees a younger earth twin. Then bam, turn around happens. Bob still sees a younger twin on earth, but bob is no longer synchronized with his adviser space twin. Space twin needs a whole new lattice of grad students, and the one he needs on Earth is a much older bob (if bob waits). This new grad student is now standing next to a much older Earth twin, who ages more slowly on space twins return trip.

Its sad that Don Lincoln tries to defend the validity of his argument, when clearly he is only partially correct and his argument is shoddy science because he tries to use authority to argue science rather than logic. "Im an authority so accept my argument as correct-just cause im me, dont worry about it dont question other aspects and viewpoints just forget about it" That seems to be the tone of his exposition. Then he makes a follow up video saying basically, whatever critiscism they have on me, basically Im still right --if you squint your eyes and dont look directli at my presentation. The point of something like this and other's criticism of his presentation is to spark debate on a subject thats many faceted--as witnessed by the many examples that exist supporting different viewpoints. In some acceleration is important and in others not. Dons too worried about the promotion of his video rather than about science---and that is deeply dangerous!

Great video. Just one minor thing to add. Those who argue that the Twin Paradox can be resolved by simply considering inertial frames and use the Triplet example to show this to be the case, miss the obvious; The ‘Triplet Paradox’ is not the ‘Twin Paradox'! The Twin Paradox requires the twin to return to Earth, and hence accelerate. The Triplet example leads to a different paradox; Namely, when B and C pass each other they both agree they are the same age. A also agrees that B and C are the same age. But B and C disagree on the age of A.

@10:50: "Whereas the observer accelerated in a rocket detects a uniform gravitational field spanning the entire universe."

I've really enjoyed this video and the one about whether or not falling charges radiate. My opinion is that in the framework of Special Relativity we are allowed to make a measurement to decide if we are accelerating. It could be an accelerometer, or just letting go of a golf ball in front of our eyes and seeing whether it changes speed. I think we are allowed to interpret the result of such an experiment within the framework of SR and measure our acceleration that way. The falling charge is fascinating, and after looking into it for some time I have to agree with Feynman. It solves all the paradoxes and preserves the equivalence principle if only a charge whose acceleration is changing produces radiation.

Should the short answer not be simply "gravity is not involved, so of course not"?

Changing the direction of travel of your spaceship, such as going in circles, is said to be "Acceleration", in the world of physics. That sounds a bit confusing. Meanwhile, if your spaceship travels in a straight spatial line, but constantly accelerates while in the process of doing so, it too in truth is also constantly changing its direction of travel. All this goes on, while the magnitude of the motion of the spaceship, NEVER actually changes. All that can be changed, is its direction of travel. Within the 4D space-time environment, the more your spaceships ongoing motion is directed to being across space, the less of your ongoing motion is now directed across the dimension of time. Taking this 4D perspective into account, throws the paradoxes out the window.

The Twin Paradox emerged from Relativity. So yes :)

8:40 There is a paradox, it's just not a contradiction. one definition of a paradox is an apparent contradiction, and that's the one we're talking about.

The answer is a firm NO. In SR, you can work in Minkowski space and integrate proper time along a world line and get the answer without contradiction. Thus SR is enough, because it is a self-consistent theory. The reason you get a paradox is when you leave Minkowski space and work in 3 + 1 frames. The paradox is not the asymmetry, its that each twin sees the other's clock tick less time on each leg, so the sum of elapsed times disagree, Ofc the paradox is resolved when you remember a line takes the form: y = mx + b, and we're just looking at "m" (time dilation), you need to include "b" (clock bias), and that changes at turn around. It's not time dilation---you can make b "run" forward or backward--it's just clock bias (see Andromeda paradox). Now you can invoke GR, and ofc it gives you the correct results, but it is absolutely not necessary. If you want to describe it in apparent physical terms, it really is paradoxical, in the limit of zero turns around (TA) time: Space twin ages zero TA, Earth Twin sees space twin age zero during TA, Earth twin sees Earth twin age zero during TA, but Space twin just picks a whole new "now" on Earth that is much later. It's not aging, it's just a new now. You know it's not aging, because if he turns around again, boom Earth twin is young again. This is the Andromeda paradox, where "now" at distant locations depended on which way you drive your car here on Earth, and ofc, the ppl living in Andromeda don't care.

1) Space and Time are separate frames of reference 2) Clocks are instruments that measure motion in space 3) the clocks cesium-133 atom is being chilled to absolute zero while the observer's are at room temperature. 4) the clock is being energized by an electrical current emiited at a constant frequency. The observer's cells get their energy from the oxygen in the environment. 5) Both clocks use the same amount of energy. The difference in readouts is due to the extra motion in space. Clocks measure motion in space. 5) astronauts experience accelerated heart rates during lift-off while the onboard clock is registering fewer clock cycles. Space and Time are separate frames of reference. Acceleration in time is energy dependent. Since the biometrics are not included, the only logical conclusion is that both twins experienced the same amount of time, and are the same age. One just experienced more space.

I do not really agree with the premise of this video, and by now we should not be calling these things paradoxes 100 years later, rather than early confusion for a few years when smart people were making sure the theory was consistent. If you had two twins A & B and B left for a trip, the video argues you need to define one (A in this case) as the base inertial frame and you need that knowledge. But that is not correct. Imagine B did leave for the trip, but they then instantly forgot who left and who stayed. if they forgot who left and A thought they had left, and then A "turned around (for want of a better description)" and went back to B (which is really just a huge acceleration given B will never stop), the result will be the same, but in reverse. It is simply wrong to imply you need to know the starting inertial frame.

I understand that the ship frame is not an inertial frame and I trust what you said, but I imagine a light clock on Earth. In the ship frame the light ray path is longer, so I think the twin on Earth is younger as it moves in the ship frame. (even though the ship accelerates and decelerates) Maybe the speed of light changes? I really enjoyed your video, you are number one! (and I'm proud to follow you since your first videos) 🙂🙃🙂

First of all - too many words and sideways explanations before explanation. OK, let say that one twin gets older. What happens when they meet again in the same space time? If I turn really fast can I meet my older self?

It is not the acceleration, it is the total spacial path. Longer spacial path means less time.

It's simpler than we all imagine, you don't always see things in slow motion when you move, sometimes you see things in fast motion, things in the direction of motion move in fast motion, if you hover above a gravitational field, the universe above you is in fast motion. If you were to move very fast in the direction of Proxima Centauri, you would see it in fast motion, because you are moving in relation to it. When you get there, your're younger. When you reach it, it's older than it would've been if its aging were only determined by the time light takes to reach you, and you catching the light rays faster as you get close to it. You don't need acceleration, you don't need to go back to "compare clocks" and you don't need to be close to it beforehand.

I don't think it's correct to say SR doesn't tell you which frame is accelerating. Because it says "The laws of physics are the same in all inertial reference frames". And the laws of physics tell you which frame is accelerating. If we use Newton's Laws for the Laws of Physics, the first Law tells us which objects are accelerating. It's basically the statement that inertial bodies follow geodesics. We can modify the laws to be relativistic, but that doesn't change the result. Acceleration, even in SR, is defined relative to geodesics. Whether or not that is entirely internally consistent is another matter and subject to much debate(see Mach's principle etc.) The point is that the "laws of physics" should provide a way to determine acceleration. GR gives us a more refined way to calculate geodesics, but that doesn't really change anything about the principle. Invoking the equivalence principle seems circular. You either have to already know that clocks tick faster ahead of an accelerated observer, which is a result purely from SR, or know all results from GR, which uses SR locally. And this has nothing to do with "gravitational time dilation", because there is simply no gravity there. A local measurement simply has nothing to do with gravity exactly by the equivalence principle. We shouldn't expect SR to reproduce gravitational effects. The time dilation between the earth twin and the rocket twin is in no way equivalent to gravitational time dilation because it is not a local effect.

Really appreciated two things about this video: 1) Your clarification that SR treats inertial frames as given - something you’re likely to get pushback on from commenters (as we once did) but about which you’re absolutely correct. 2) Your noting that proper acceleration as a solution doesn’t generalize to GR - something almost everyone who treats on the topic of the twin paradox overlooks. In our long study of the twin paradox, we learned that, within the context of the current theories of relativity, there is only one “resolution” to who is younger - and that is whichever twin traveled the shorter spacetime path. In flat spacetime, this will always be the accelerating twin, while in curved spacetime considerations of the metric will determine who travels the shorter spacetime path. But of course, if one asks, what is the physical meaning of spacetime distance - the only answer the theory can give is that it is the amount of proper time which elapses on a co-moving clock. So the “resolution” to the twin paradox is precisely this: the twin who comes back younger is the twin who experiences less elapsed proper time. Quite tautological. The problem you may or may not be grasping is that Relativity is not a theory of causes, it is a mathematical description of correlations between measuring instruments/coordinate systems. And the paradox of the twins is essentially not asking what breaks the symmetry, but asking what causes time dilation in the first place. And as both we know, Relativity can’t answer that question. Indeed it seems you still have not grasped the full significance of the one-way-speed-of-light problem. If nothing requires observers to choose epsilon = 1/2, then the twins can choose appropriate epsilon values such that they both agree that it is the traveling twins clocks that are running slower - and so there is no paradox in the first place. Of course, everyone’s understanding progresses at its own pace, and there was a time when we too still believed relativity to be correct, and dismissed all those who told us that only an ether could explain time dilation as essentially crackpots. Sometimes one must taste the medicine they dish.

Bro is Length contraction Really An effect of superposition or Quantum wave mechanics ?As Dialect proposed in his interpretation of Relativity and Length contraction can You make a video about it

Very clear, as usual. Interesting "fact": in a not so popularly known formulation of the paradox, one twin is on earth, subject to earth's gravitational acceleration (ok, the floor imparted acceleration upwards... of 9,81 m/s^2) while the travelling twin starts from a high tower. Bear with me; the final makes one reflect on the nature of 3D-space. Well: Since he's starting from a high tower, with lesser gravitational strength, he can "use" the difference (say he's subject to 9,80 m/s^2, not 9,81) of 0,1 m/s^2 to move further up. As he gets away, the gravitational strength diminishes, so, in order to maintain his acceleration equal to the other twin's (=9,81 m/s^2) more and more "moving" acceleration becomes available. When the earth's gravitation becomes negligible, due to the *inverse square law* , the 9,81 m/s^2 are used practically only to increase his velocity. Then, to invert the motion he takes on a speed higher than orbital velocity around the - now far away - earth, so that he must maintain himself centripetally accelerated at 9,81 m/s2 while turning around, and finally heads back home, where he then decelerates, always maintaining his "perceived weight" at 9,81 m/s^2 against the spaceshift's floor. And, when he returns, he's younger. But the difference is only one: earth's gravitational field is spatially limited, whereas the "apparent" gravitational field arising from the (absolute) acceleration is not. So when the "fictitious", spatially infinite gravitational field acts, the one making time go faster on earth (therefore making the earthbound twin age faster) *from the travelling twin's perspective* , it acts at the *distance* between "orbital" (not really) motion and the earth. We call it "Radius", obviously. Now: different journeys with combinations of parameters: acceleration, journey duration, distance reached, etc... will result in different experiences, and different age offsets between twins. For example: A- if you decide to "orbit" (not really: you have to maintain centripetal acceleration of around 9,81 m/s^2 = 1 g) *very far away* , you'll experience 1g centripetally only to sustain circular motion; but here, far from earth, the circle is very wide: much time is needed to complete at least 1 circle to head back home. The circumference is = 2*pi*Radius. B- decide for a lower "orbit"? but then you've got to accelerate less - and for a shorter duration, as you're not so far away and the circumference isn't big - to invert the motion, because there's still a non negligible earth's gravitational field _helping_ you turn without accelerating. Being - "nearby" means that the "fictitious" gravitational field that you feel acts at a lesser distance and makes the earthbound twin age faster (from your perspective) at a much much lesser rate during that phase of accelerated motion, than in the previous (earth far away) example! Also, your proper time offset from pure SR isn't big, because the whole experience takes less time, distance, etc... Now, maintaining the relation between radius and circumference (2*pi), suppose we ask for the *gravitational strength distance relation* that has to be in place for a traveller that stays in the loop for a certain fixed duration and ends up experiencing a certain *fixed* age offset between stationary and travelling twins. The result is NEWTON's INVERSE SQUARE law for the gravitational field!!!!!!!!!! (the initial "tower" is only a kickstarter, a "trick" and can be reduced to zero at the limit)

Didn't you mention in a previous video that you can rotate your accelerometer by 90° and know that if there's no change then you are in an inertial reference frame? (Proper acceleration will make your accelerometer different in each orientation.)

I'm thinking time has to be a dimension in whatever distance function you are using. sqrt(t^2+i(t)^2+j(t)^2+k(t)^2), or dt, whatever.

I think it is easy to proof that relative velocity difference does not necessarily cause relative time dilation. Instead of twins consider triplets. L travels to left, E remains on earth, R travels to right with exactly same, but exactly opposite acceleration as L. There will be no time dilation between L and R, despite the HUGE difference velocity, but both will have time dilation against E. Also, if we only use SRT with straight lines then infinite acceleration within zero time at the starting, ending and turning point must be assumed. This is impossible to calculate. When it is neglected, we get an error.

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Einstein's 1905 paper establishes a unification of Galileo's Principle of Relativity with Electromagnetism - it is not a theory of spacetime. Relativity is just general relativity and the machinery of the special theory can be used in the special case of the ground state gravitational field (the gravitational field such that the Riemann curvature is zero on all components).

If you think about time keeping (like a light clock) as an electric oscillation on the smallest possible scale in any object you will find that any movement will result in a slowing of this time keeping. Explanation: If you look at a particle as a circle and the time keeping as an electric signal going from one side to the other and then back again (oscillating) it will take longer to make a cycle if the whole thing is moving. Einstein's famous light clock in a train works as well if it is laying down as when it is perpendicular. Seeing at time dilation this way points to that there is an absolute "Zero speed" in the universe. Acceleration has nothing to do with it other than you must accelerate (or decelerate) to get a different speed. That people stay younger when traveling fast is really no different to that frozen meat stays good longer than fresh meat. This is my opinion as it all makes sense to me. Also why shouldn't there be a "Zero speed"? We have a zero temperature and we have a maximum speed. It is just very difficult to find "absolute speeds" as we can't measure Electro Magnetic Emission (like light) in one direction only. Not yet at least. Time itself is in my opinion a momentary thing. We have a past that we can't change and a future that we don't know. That is why I say "Time keeping" (or time counting it should be). Also how can a future be deterministic if radioactivity is random? Radio activity can influence every thing.

The variables in gravity math are NOT causal. Number analogies are not an understanding, and that math can lie to you. "The wheels on the bus go round and round." This song describes everything you see a bus do EXACTLY like math does, but you wouldn't agree that wheels going round are causal - WOULD YOU? Dimensions are a number game that helps math work, but you cannot show me dimensions 1 or 2 in real life, and you have a series of theories that ADJUST these fake dimensions. What if that math is lying to you? It's the only thing taught to anyone. Even if it was obviously wrong, in these conditions, you wouldn't see it, because that's how paradigms work.

I enjoy your presentations, but I have to disagree vehemently with this one. I believe that you have things exactly backwards when it comes to the Equivalence Principle. The way that you (and very many popular explainers of General Relativity) describe it is this way: To calculate the effect of acceleration on clocks: 1. We invoke the Equivalence Principle, and transform the problem into an equivalent problem involving gravity. 2. The feeling of acceleration is interpreted as a kind of gravitational field that suddenly turns on. 3. We use gravitational time dilation to calculate the effect of this gravitational field on clocks. Okay. What's wrong with this description? Well, ask yourself how gravitational time dilation is computed. The answer is exactly the reverse process. To calculate the effect of gravity on clocks: 1. We invoke the equivalence principle to transform it into an equivalent problem involving acceleration. 2. The gravitational field is then interpreted as the inertial forces that result from acceleration. 3. We use special relativity to calculate the effect of this acceleration on clocks. The latter description is the way that Einstein DERIVED gravitational time dilation. By applying Special Relativity to accelerated clocks. To quote WIkipedia: Gravitational time dilation was first described by Albert Einstein in 1907 as a consequence of special relativity in accelerated frames of reference. This was 8 years BEFORE he developed a theory of gravity. So you've got things exactly backwards. Einstein didn't use the equivalence principle as a way to apply gravitational theory to accelerated observers---he used the theory of accelerated observers (as described using Special Relativity) as a tool for developing his theory of gravity. You don't need the equivalence principle to calculate the effect of acceleration on clocks. You need the equivalence principle to calculate the effect of gravity on clocks. The equivalence principle allowed him to reduce an unsolved problem---how does the Earth's gravitational field affect clocks--to a solved problem--how does acceleration affect clocks. This is a confusion that has persisted in physics ever since Special Relativity. Even Einstein took some time to get it straight. Many people think that Special Relativity is a theory of inertial observers, and General Relativity is a theory of noninertial observers. That is completely wrong. Special Relativity is a theory of FLAT spacetime, while General Relativity is a theory of CURVED spacetime. You can handle accelerated observers in Special Relativity in exactly the same way that Newtonian physics can handle accelerated or rotating observers. It's just a change of coordinate system. Newtonian physics is usually presented using inertial Cartesian coordinates. Newton's laws look the simplest in those coordinates. But if you really want to, you can rewrite them using curvilinear or accelerated coordinate systems. It's just calculus---if you know equations of motion in one coordinate system, then you can use calculus to figure out the equations of motion in another coordinate system. But things are messier in curvilinear or accelerated coordinate systems. In those coordinates, there are apparent "fictitious forces" that have no physical cause, but are just artifacts of your choice of coordinate system. These include (1) the "g-forces" that you feel when you are accelerating, (2) the centrifugal force that is felt when one is traveling in circular motion, (3) the Coriolis force that is felt when you move in a rotating coordinate system. These forces are "fictitious" in that they don't actually result from interactions with matter or fields, but they are extra mathematical terms that appear in the equations of motion. Newtonian physics works perfectly well in non-inertial, curvilinear coordinates, it's just a little more complicated looking. In exactly the same way, Special Relativity works perfectly well in non-inertial, curvilinear coordinates, as well. It's just more complicated looking. If you try to apply Special Relativity to accelerated observers, or to use it with curvilinear coordinates, you get "fictitious" forces in the same way that Newtonian physics does. These fictitious forces in Special Relativity do not only affect the motion of objects (in the way the Centrifugal and Coriolis forces do) but also it affects clocks. This is not a new effect that requires General Relativity for justification--it is an effect that is derivable from Special Relativity by just using calculus to change coordinates. The connection between General Relativity and curvilinear, noninertial coordinates is that in the presence of gravity, there ARE no inertial coordinate systems. So curvilinear and noninertial coordinates are required to do anything. And those coordinates have effects on the motions of objects and on the elapsed time on clocks, just as they do in Special Relativity. So there's three different stages in going from Special Relativity to General Relativity: 1. Special Relativity in flat spacetime using inertial, Cartesian coordinates. 2. Special Relativity in flat spacetime using noninertial, curvilinear coordinates. 3. General Relativity in curved spacetime using noninertial, curvilinear coordinates. 4. A theory of how matter and energy cause spacetime curvature. Going from 1 to 2 doesn't require a theory of gravity, it only requires calculus. Going from 2 to 3 requires a theory of curved spacetime, which is also not fully a theory of gravity. You need 4 to get a full theory of gravity.

The original paradox addressed by Einstein is not about twins aging at different rates after one of them started a journey from Earth at high speed and returned back years later. It's about identical clocks ticking at different rates when moving relative to each other according to special relativity. For clock A clock B is ticking faster. For click B clock A is ticking faster. That is the original paradox which could be called "the identical clock paradox". And it was solved by Einstein by addressing it as a problem of simultaneity of events, not by using gravity or accelerated frames of reference. You mention you cannot write the same spacetime diagram for the travelling observer because it only applies for inertial observers but as far as I can see the travelling observer is also inertial, i.e. not accelerating. That's unclear to me.

Maybe time doesn't exist (man made phenomena) and should be seen as a sequence of events.

Out of curiosity, though I completely understand the physical manifestation of the measurements, of two Reference frams. What is occurring in the space of two different frames. Ie. At the quantum level, what is occurring in the interactions, especially in different gradients of a gravitational field. Ie not simply the passage of time but the physical mechanics of the gradient in time dilation. Like... Is there an adjustment (phase change) to renormalization. I'm curious if there is research on the subject that you may provide links too.

For a second i thought matt parker got hair implants

Dont you have to go to the future to go back to the past?

I don't get why people don't get this. If two people are going different velocities, then the one that will be younger is the one that decides to change to the other's velocity. The actual definition of how much time passes is based on reference frame.

Very clear-cut explanation!

Sweet Jesus, could you please answer this yes or no: THE TWINS-PARADOX IS SOLVED BY CONSIDERING THE ACCELERATION.

Very nice explanation!

No

Explain why GPS doesnt use einstein equations? Contrary to what many believe...

Hi…the person that is in the ship accelerating does not feel an uniform acceleration…it’s shown in the Rindler diagram,,everypoint in space has a different hyperbola that describes a different acceleration..

Yes, just amazing and what I expected. Special relativity can handle acceleration and even the time gradient of the gravitational field by hyperbolic geometry, or two frames, or worldlines arc length, but it is itself against its first postulate, that everyone can claim to be stationary. In a spacetime diagram, if the moving twin (the zigzag line) was chosen to be stationary (straight line), it would mean that the structure of the diagram must change in such a way that it keeps his worldline shorter, kind of like changing from Cartesian to polar coordinates doesn't affect the path, or making the earth flat on a map doesn't affect the path. But for this mathematical assumption to be known, we must have the information about who is inertial in the first place. If we don't provide this information, the twin doesn't even know what his spacetime geometry is. So, General Relativity fixed that by allowing him to claim himself to be stationary no matter how much he accelerated and how many times he experienced a gravitational field, which allowed both of them to claim to be stationary.

How is using GR in this case better than using SR? SR: Rindler coordinates--> solution. GR: metric-->geodesic equation-->Rindler coordinates--> solution. Identical results, SR faster. How does using GR help? Can someone please explain this to me?

Error: 3:02 A non-zero 3-acceleration does NOT imply a non-zero 4-acceleration, and neither does a zero 4-acceleration imply a zero 3-acceleration.

I am confused by something I thought you said: my clock will tick slower if I am moving at uniform velocity wrt another, external Observer. I thought that wrt to my own inertial frame of reference, there is NO time dilation. So my clock would APPEAR to tick slower to the Observer but not to ME. I hope you agree so far. In your example, my elapsed time would be 5.75 years, from my perspective, before I turned around, although to the Observer it would seem like 2.84 years. When Observer and I meet again, after I turned around, my clock would have recorded MY time, which would be 11.5 years, not the time (5.75 years) that Observer thought I had clocked. The Observer looking at my clock when we are “sitting across a table and wondering who is older”, is no longer the scenario where we were moving relative to each other at near-light speed. My point simply is: my clock recoded my time, not the time perceived by Observer. So the so called “paradox” may be a “red herring”. Am I missing something?

A few years ago, as an interested layperson, I came up with the following concept to better understand the twin paradox: shells of light. When Alice moves towards Bob, she breaks through Bob's light shells more frequently, causing her to see Bob in fast motion (imagine a periodic signal emitted by both and counted by both). The key idea is that these light shells contain all the information about the relative present. Accordingly, one travels into the relative future or past of the other. For example, if Alice is 4 light years away at Alpha Centauri and Bob waves to her from Earth, and Alice instantly travels to Bob at the speed of light, no time would have passed for Alice, and she would be the same age upon arrival as she was when Bob last saw her in his telescope - since Alice traveled with her own light shell. Conversely, Alice would have broken through many of Bob's light shells during her journey, causing her to see Bob in extreme fast motion and experience him as 4 years older upon her arrival, according to the number of light shells she passed through. Essentially, both would just need to count their relative light pulses. For the full picture, you must take into account the change in direction and acceleration, but the basic concept should hold. Edit: Also, the situations in the twin paradox are not symmetrical from the start. If Alice travels to Alpha Centauri, 4 light years away, at the speed of light, she experiences it as follows: She leaves Bob, arrives immediately, and sees him as he appeared to her "just now," because she has traveled with his light. Conversely, Bob sees Alice disappear. He sees her arrive at Alpha Centauri after 8 years, appearing as she did 8 years ago when she left him, since no further light from her reached him in the meantime. If Alice returns to him shortly after her arrival, she sees him again in the next moment, but suddenly 8 years older - in that one moment, she has received 8 years of his light. From his perspective, she returns and is immediately back with him, not having aged, because he received no further light from her in the intervening time.

Só acceleration is not relative then? If an observer B is accelerating away from A then this is an absolute universal fact and B will not assume A is in fact accelerating away from him? So not all frames of reference are equally valid?

While relativity comes down to making good predictions for what instruments will verifiably record, and so no evidence has yet contradicted it, it’s outside these cases of verifiability that I take issue. The paradox is not what will happen when we verify what will happen (upon the twins return), but rather, what is happening at a distance. When the twins are traveling apart or towards each other before the return, who is aging less. Under the relativistic model, Depending on who you ask and their frame of reference, all aging possibilities are happening simultaneously. Both twins are aging less, more AND not at all relative to the other, and by varying degrees on a continuum. This to me points to a model error.

Great video. I was with you until you said you have no tools in SR to interpret the force, but that's not true: they will see a change in red/blue shift. You can actually watch the changes in all clocks around you via light. The trick with the accelerometer is that it only works when you fire your engine, or stand on the ground pushing you up in a gravitational field. If the whole accelerometer (springs and all) are accelerated uniformly, it won't tell you anything. But light... ligt will tell you the whole picture.

Equivalence and Acceleration doesn't solve it though... assume the acceleration of your engines goes from 0g to Xg; your computed time dilation would then be a square wave from 1 to whatever dilation that gravitational acceleration gives you, and then back. That's a simple sum doesn't even really require calculus... but whatever that is, you could change the length of the trip such that that does not match the same total dilation that happened. (did you even attempt the math?) The postulates of special relativity should be refined to say 'the speed of light that travels the same distance in two-ways'. Second - the postulate that all physics is the same in all frames is an assumption that cannot be proven... it's also hard to falsify at our current level of technology though. Parker solar probe is only 191km/s - which is 1/2 of our speed through the universe, though I suppose the additive velocity might at times be 1.5x our speed... that's still a small fraction of the speed of light, I suppose they should include a particle accelerator and muon detector on the next parker-space-probe-like craft... and measure a different anomalous G-2 result.... the difference between experiment and measurement is 0.012%... this is exactly the fraction of the speed of light that the solar system is moving in the universe. (Is physics REALLY the same in all frames?)

I am afraid there is a very important conceptual mistake in the explanation. It is definitely not correct to say that in special relativity (SR) every observer is inertial by definition. SR is not a relationist theory, i.e., motion is not merely relative but Newton's absolute space reigns. The accelerometer absolutely tells you if you are inertial or not. Newton's absolute space is also present in special relativity (even in GR). Inertial frames are those where the principle of inertia holds and that does not happen in arbitrary frames. Another way to define inertial frame is (according to, for instance, Landau & Lifshitz) that time is homogenous and space is homogenous and isotropic. Those properties of spacetime do not hold in non-inertial frames. The author (who I used to follow and admire) should discuss this issue with an expert and see if he can correct his presentation.

Dialect

Omg STR is about inertial motion only! That is why STR has always had a twin paradox and was rightly considered as nonsense. Don’t believe me then read Einstein’s paper from 1918. He was force to give a solution to this from all the criticism he got and he used GTR. Basically this means he is abandoning STR. You need to look at the history. Try “Relativity from Lorentz to Einstein: A guide for beginners, perplexed and experimental scientists” Lots of references to relevant literature. Here are some others, “Science at the crossroads” by Herbert Dingle, “A scientific adventure. Reflection on the riddles of relativity” by Ian McCausland and the recent “New Relativity in the Gravitational Universe” by C S Unnikrishnan. Another is Tim Maudlin’s “The Philosophy of Physics. Space and Time” where he also says that acceleration does not solve the twins paradox but gives his solution … which also doesn’t work😂

There is no twin paradox because they are always the same age in a flat space without gravity. It's just an observer illusion, and is not real. The time period is the same on both ships.

a signal travelling a longer distance doesn't mean time is slowing down.. its ridiculous. And speaking of paradox. If you and light are travelling in the same direction and your accelerating and your time slows down it keeps the soeed of light c, but if light is coming towards you and you are moving towards the light accelerating or not , your time slows down meaning its no longer c, its much faster the speed of ç. It only works when you and light are travelling in the same direction, relativity is pure imagination and not true

Have you heard of the channel: ​@ChrisTheBrain ? He has some really interesting videos about physics, but I can't tell whether or not they're nonsense. I'd be curious to hear the opinion of someone more knowledgeable