Even More Paradoxical: The Twin Paradox in Curved Spacetime 

Thx

Agreed

Yes it is, there are 3 others i believe , all equal top notch. Then the next 5 are getting really good too. Ps I've been watching Richard Fienman's lectures, they are posted, and they are absolutely fantastic. So God damned good Dialect himself will tell you I'd bet

Try David Butler

@@KINGFAROOQ1216 Which other ones?

yeah, becouse he is backpedaling and trying really hard to hide it. The acceleration really solves the original twin paradox becouse in the flat space-time this causes the space-time path to be longer. He just generated buzz by basically calling everyone else stupid and made some outrageous claims. Then started to describe more general problem and described more generalized solution to the problem and called the original solution wrong. There is a reason why every explanation of twin paradox involves acceleration. People who are just starting to learn about special theory of relativity need simpler explanation that does now involve general theory of relativity.

What's amazing is how all the established wisdom of "consensus science" got such a basic question of a theory that's been around for over 100 years wrong. This is a great lesson in not just accepting conventional wisdom, even by experts, if it doesn't make sense to you. There's room for discoveries in even some of the most trodden ground.

@@chrimony Can you elaborate? What did "consensus science" get wrong?

@@rsm3t I think it was the idea that acceleration is the reason for the difference in aging/time of two bodies in space-time.

there is also no mention that a rocket would only accelerate until reaching escape/terminal velocity, and then accelerate when turning back. the rest of the journey would be at constant velocity.

@@carlosgaspar8447 that is discussed in previous parts

See, for example, Time, Topology and the Twin Paradox Jean-Pierre Luminet Laboratoire Univers et Théories, CNRS-UMR 8102, Observatoire de Paris, F-92195 Meudon cedex, France

@@nadirceliloglu397 I guess I just go with my gut then next time. ;) But seriouesly, I am sticking with this one now because it makes sense to me. If you got a good article or something with a better explanatioon, please let me know.

Curvature of spacetime won't be affected

No. You can have twins paradox where both twins are in inertial frames of reference. One twin can be in a high circular orbit, the second twin can be in a low eccentric orbit that tangentially intersects the high circular orbit. The twin in the high orbit will be younger. Neither twin is noticing a change in momentum, nor any acceleration, nor any force at all. They are both in free fall.

@@hdthor but the in the lower, excentric orbit, has to go faster to stay in orbit, so the extra speed compensates for the extra proximity to the gravitational field.

@@nadirceliloglu397 Nobody cares buddy.

@@nadirceliloglu397 I’m sure you have it all figured out, just like everyone else on the internet. Post a video explaining it instead of wasting time with these worthless posts. You think I’m going to believe you just because you said so? That’s not how any of this works.

@@nadirceliloglu397 lol get a grip

Newton's Laws of Motion. F=ma, Force equals Acceleration. Acceleration equals Force. In a gravitational environment, force is applied to an object. That object becomes accelerated. In time or in space? If we look at nasa's flight data, we see that, during lift-off, heart rates are accelerated. Accelerated heart rates equal shorter lifespan as evidenced by hummingbirds. If we properly analyze the Hafele-Keating and other flying clock experiments, we can see that both clocks used the same amount of force and thus experienced the same amount of time. The lower acceleration reading went into the extra distance traveled. Time doesn't slow down, it just gets spread out over a greater distance. Does an accelerated heart rate cause you to age faster (physical appearance) or just die sooner (shorter lifespan). There is some indication that zero gravity (less force) will extend a person's lifespan (nasa's twins experiment). You cannot go by the clock on the wall as it is in a different frame of reference than the observer. It's Force is metered out at a constant rate.

It will be very interesting to hear if there are fatal problems with the spacetime path-solution as well, as you indicate. Since 1985 I have thought this was the correct solution to the paradox, but I look forward to be corrected 🙃

We pick 4 random points in space and time and we make a 4D grid. That's our spacetime. If we allow the grid to be infinite in all dimensions, then that grid encapsulates the entire Universe. Someone else is going to pick 4 other points at random and from his perspective his grid wont look like our grid, and our grid won't look like his. Why can't we unify both grids, in a way that all the possible grids are all the same grid - just seen from diffrent points of view? Imagine a single 4D hyperbolic grid, projecting a 4D Euclidean grid to every observer in the Universe. They will see their own grid as we see Sun's reflection of itself when it hits the sea. But, that bright line that the Sun creates at the sea - is unique to every observer, because depending on where they are, that's where they will see it. Its caused by the Earth's curvature. Italo Calvino the Italian poet and author, called it "the sword of the sun" www.ampersand-ampersand.com/images/screening/theswordofthesun.pdf in his book "Palomar", and its unique for everyone of us. That doesn't mean though that there are infinite versions of our Sun. Our Sun is a single entity and so is our spacetime. So in that sense we should be able to define absolute motion in respect to that spacetime grid - since things DEFINITELY age more or less than others. Or in other words - since 2 twins can separate and come back and one is younger than the other - there is DEFINITELY something absolute relative to which they moved at aparently different ways.

@@-_Nuke_- It's an interesting point of view. But that should mean that the principle of relativity applies only to an euclidean geometry spacetime, while in this particular hyperbolic one that you postulate, which generates all possible euclidean points of view, everything becomes absolute. But the Minkowski metric is in itself an hyperbolic geometry, and the twins paradox takes place in it as well. So, the Minkowski metric is not the absolute metric you are talking about and there should be other one that encompasses the whole spacetime and generates by projections all other possible hyperbolic and euclidean geometries. I'm at the boundary of my knowledge, here. Maybe, just maybe, there is another type of geometry at play here that we have not been able to identify. Anyway, the whole idea of an absolute geometry which generates the relative ones is nevetheless interesting.

But spacetime intervals are invariant. You might disagree on time or space, but everyone agrees on spacetime intervals.

@EliteTeamKiller S.I. are invariant in a Lorentz transformation, but space and time vary and the issue is precisely to know who ages more (or less). So, to derive time. Suppose two spaceships meet. Each one sees the other zipping by and each can claim to be at rest. Who ages more? We could say: "Who cares? They'll never meet again, so the question has no meaning, as they'll never share an event again". But, now let's suppose the universe is an hypersphere. After a long time, the one that is moving (either A or B) zips by again. Who has aged more, from each other's point of view?

The 4-acceleration vector or proper acceleration is a measurement of 3-acceleration with respect to an inertial frame. The context for defining inertial or non-inertial frames however does not exist within the framework of either special or general relativity (or worse, such frames are defined circularly, via absence of a 3-acceleration) leaving 4-acceleration to be as much of a relative concept as 3-acceleration.

@@dialectphilosophy Again, this is wrong, the proper acceleration is a Lorentz scalar.

@@dialectphilosophy 4-acceleration is defined as the covariant derivative (or the connection) of the 4-velocity in the direction of itself. The connection is defined to be coordinate independent, and 4-velocity is defined as the vector field whose vectors are tangent to a path in spacetime, and this path is also coordinate independent since it's defined as an assignment of a set of points on the spacetime manifold. Therefore 4-acceleration as a vector field cannot be relative. 3-acceleration is relative because it's merely the spatial components of the 4-acceleration, which depend on the coordinate frame you choose to decompose the 4-acceleration.

@@Etc2496 Your confusion here is pretty simple. In the context of the theory of General Relativity, 4-acceleration is, as you write, defined and treated as 'absolute'. However, a model is not reality, and merely regurgitating textbook definitions of what 4-acceleration is or isn't doesn't alter the fact that General Relativity offers no definition for what characterizes absolute acceleration (other than that which is determined by an accelerometer, but an accelerometer can easily be demonstrated to be an instrument only capable of making relative measurements.) So when we say "acceleration is relative" in our videos, we are NOT saying that General Relativity treats acceleration as relative (a mistake many people actually do make, and which we address in our Einstein video) since the framework of GR considers acceleration to be absolute. Rather, we are asserting that this assumption is fundamentally and logically inconsistent and does not meet the proper criteria of an empirical science, so in fact GR cannot be an entirely complete theory. Just as the assumptions of absolute space and time were realized to be fallacious by philosophers centuries before the advent of the theories of relativity, so too is the concept of absolute motion obviously flawed and bound to fall sooner or later.

@@dialectphilosophy I mean, yes, a model is not reality. However, you and me are both talking about GR, which is first and foremost a mathematical model, and therefore it makes sense that we talk about its mathematical framework as well as how it explains physical phenomena according to such framework, since we don't yet have access to a better model for reality. In GR, an accelerometer simply lets you distinguish between if you are following a geodesic path or not. If you are not, then you are in a state of acceleration and the accelerometer will confirm this. In real life, this is indeed what we observe, since there is a difference between being in free fall (in a geodesic) vs standing on Earth's surface, for example. The mere fact of whether or not you are following a geodesic path IS NOT RELATIVE, since it depends on the inherent geometry of spacetime, and not in frames of reference. Therefore, being in a state of acceleration cannot be relative, since otherwise it would mean that spacetime geometry depends on how you observe it, which is not what we see. The problem with your last paragraph is that, while yes, what you are saying may be true, you are as of now only speculating about how the universe works, since as I said before, GR is one of the most successful theories we have come up with. You are free to make such hypotheses, I also do this, but keep in mind that GR still hasn't been superseded and there are a milliard of other possible models that could equally as of now replace GR. You are correct that GR implies that some stuff is absolute, but this is just a requirement of the principle of relativity, although I don't know what you mean by absolute motion.

I dont advise.. you do a phd in relativity may be to work on a better correcter to gps system only to end up not using relativity. Just dont

Not at all! Our quest to resolve the twin paradox took us into studying General Relativity; eventually that threw us back towards Special Relativity. We essentially address the paradox problem again under the lens of Dynamical Relativity in "What Time Dilation Actually Is", and will probably devote a video towards it in the near future.

General relativity is pseudo-science. It wants you to believe that mass curves space when in fact, motion curves space. A rotating body creates a circular path of increasing rates of acceleration as the radius increases.

you didn't watch the entire video did you

Question: can we then conclude that the twins cannot know which of them is older and younger untill them reunite (assuming they dont know each others paths in spacetime beforehand)? This is quite interesting indeed... very much contrary to the impression given in the usual treatment of the dilemma.

@@imaginingPhysics Or maybe each of them live in their version of multiverse...This paradox is confusing. Maybe time is just an illusion. And particle with force/energy applied to them will undergoes change in state of matters slower, thus appears experience time slower? Because we can only measure time by using the change in state of matters, biologically, chemically, or mechanically.

@@imaginingPhysics if they're not accelerating relative to each other, they will always agree on who is older. There is no paradox unless there is acceleration.

Any suggestion of a video on that Hubble flow? Thanks

​​@@Littleprinceleon Darn. I replied, but I guess I cannot use links. Uhm. I wrote I don't often watch popular science videos anymore since they are often misleading as Dialect shows in His video about gravity (of course) not being caused by time dilation. It's entertainment rather than education so it can be fun, but imo laypeople should discuss such videos before taking it to seriously. One cannot use youtube as a serious reference of course. But anyway just google "Hubble flow" and "peculiar velocity". The Hubble flow is basically motion caused by the expansion of the universe solely and peculiar motion involves velocities that deviates from this Hubble flow. So for high peculiar velocity observers and observers on Earth (with a low peculiar velocity) gives a difference in proper times. So one could use that to solve the "paradox" (even more realistically). And it shows that you cannot simply "remove" the earth in this paradox (when taking it this seriously). (When we speak of the age of the universe, it's meant the Cosmic time measured by fundamental observers; not deviating from the Hubble flow (too much) and far away from strong gravity sources.)

For us and anyone, it's all time. It's the amount of coordinate time and space of others moving relative to us that changes.

@@renedekker9806 “you should always draw the spacetime diagram in an inertial frame”, But this is just the point: all the twins are in inertial frames! So you can choose the travelling twin as being stationary on the spacetime diagram!

@@renedekker9806 “the twin that leaves first is in an inertial frame the whole duration of the trip. So we can draw the spacetime diagram in her frame. “, No, both twins are in inertial frames, the one twin just leaves later on! So you can draw the spacetime diagrams from both viewpoints and hence obtain contradictions!

@@renedekker9806 “In her frame the second twin first moves away and then comes back, and therefore the second twin will age less.”, But what about the viewpoint of the second twin, why ignore it? They are both in inertial frames, so why is there a preferred frame?

@@renedekker9806 “the second twin is not in the same inertial frame the whole time.”, But neither is the first twin! The first twin also have to launch from earth and land on the star. So the twins are symmetrical- both have to accelerate and decelerate to reach the star!

@@renedekker9806 Thanks for your reply. Some relativists will argue that the turnaround (when you have deceleration and acceleration) have a profound effect. For example, RoS (relativity of simultaneity) is ioften nvoked to explain why the travelling twin sees the earth twin’s clock running faster (not slower). If the changing of frames of the travelling twin at the turnaround have no influence, then both twins will predict the other’s clock to be running slower- a physical paradox! So at the turnaround it is postulated that changing frames (deceleration then acceleration) have a profound influence on the travelling twin’s prediction of the earth clock! But what physical reason is behind this (other than fixing a wrong prediction of SR)? One can also argue that the travelling twin is really the earth twin and the stationary twin is the travelling twin! If you apply the same procedure as above (that the travelling twin predicts the clock of the stationary twin to run faster at the turnaround) then the prediction of SR is that the earth twin measures the travelling twin’s clock to be running faster! Hence a contradiction is again obtained.

The Twin Paradox only exists in Einstein’s fantasy universe called Spacetime. Spacetime uses acceleration as the basis for its physics. Using force as the basis, the Paradox is easily resolved by one simple experiment. Synchronized clocks. One stationary, one accelerated. What is the force difference between the two (how much energy did each clock use)? When you try to define acceleration with acceleration, you can make all sorts of outlandish claims. Like time-dilation, space warping, mass increasing with acceleration. Newton's Law of Motion F=ma disproves Einstein’s relativity theories. Motion is absolute because force is absolute. You can't go faster in space because at c, there is no mass left to accelerate. Clocks measure acceleration, not Force. Synchronized clocks measure relative motion, not time. F=ma. Force is the same, mass is the same, acceleration changes. Acceleration in space or acceleration in time? The caesium-133 atom is in cryostasis so clocks measure acceleration in space. Spacetime is Einstein’s fantasy universe concocted to peddle his theories Why people still worship him is beyond belief.

Thanks for watching, and well-said!

@@dialectphilosophy Hi nice channel. Are you familiar with the Reductio ad Trivium on problem solving?

If it doesn’t generalize to curved spacetime then it can’t be responsible for breaking the symmetry, and could therefore only be a correlate phenomenon, not a casual one. That’s the whole point of the video

Someones been watching Brian green

Yes, he is wrong. Science is not dictated by authority, but by reason.

They really do need to figure out the flaw in how they make them GPS clock, I hear it's because in Thier math equations they don't add the the speed of the satellites to C because " nothing can travel faster than light...

​@@dexter8705in BB

I dunno why the video author doesn't understand the stuff in the last paragraph especially. They've repeatedly said in multiple videos that acceleration in not the answer to the asymmetry in the standard Twin paradox example, because the same reasoning can't be applied to an example in curved spacetime. Duh! Nobody said it is. Technically, even in curved spacetime, acceleration (proper) is still the reason for the asymmetry in time dilation. Just not in the very common sense of the word, including the common misunderstanding that there is a force acting on falling bodies in gravity. In curved spacetime, it is the twin who is positioned still w.r.t the Earth, and not the twin who is free-falling in an orbit around the Earth, who is accelerating. So, following the same logic as the standard example, the orbiting twin will be the older one. In one of the other videos, the video author also says that accelerometers don't solve the issue, when in fact, they absolutely do. In all these cases, if both the twins carried a pair of accelerometers and they were put in whatever spacetime and with whatever forces acting on them, and we use their readings to calculate when and by how much the time dilation asymmetries occurred we can always tell who is going to be older. There won't be any paradox.

I am calling bs on the paper. The case of using thrusters to levitate is exactly like sitting my butt in my chair, in both cases passing through time slower than a free falling frame. There's no reason to think that the levitating somehow has a reversed effect. Acceleration is the breaker of symmetry as usual.

After 10 years of casually watching dozens of of videos on the topic and always coming away finding something sketchy about all of them, and even more sketchiness in comment sections by people who not only proclaim they have finally come to an understanding, but proclaim the channel owner as some kind of pedagogical second-coming in an explanatory power rivaling the talents of Richard Feynman, I finally stumbled upon this obscure outpost and watch almost all his videos in a single hour and a half sitting. This man is seriously underrated and under-represented in youtube's right sidebar. It's the physics equivalent of Google News sidebar of Fact Check, Polygraph, and the like.

Hi, thanks for watching, and great question! Technically, the radially-traveling twin doesn't have to be "launched" -- he can start out already traveling at a high velocity. This might be difficult to imagine with twins, so instead replace them with clocks. When the two clocks start out in a coincident position, we can have one clock that is already traveling at a high velocity and one that is not, and we can also have them both read the same time (the same age). Then, when the clocks are reunited/recombined, the free-falling clock will show more elapsed time. No acceleration whatsoever needed. Additionally, its not clear that the initial acceleration when the twins share a coincident position would make much of a difference anyhow; in the traditional twin paradox in flat spacetime, when Bob blasts off of earth, no difference in aging results between him and his sister, since they both occupy the same "height" in the pseudo-gravitational field that results. Hope that clears up your confusion.

Clocks is a better example because we can image the many gps and related satellites that are currently orbiting earth.

@@dialectphilosophy The problem with assuming that one twin (or clock) is already traveling at a certain velocity is that the twins (or clocks) no longer share a frame of reference at the initial state. There's no paradox when starting with two different frames of reference, one of which is accelerating to stay in place and the other is is in a freefall, but with enough velocity to travel away from the planet, then fall back.

@@Mythago314 You can have both twins start in the same reference frame by having them in free-fall together, then you can have one twin accelerate to stay-in-place. The respective aging of the twins would then still be the same in this case as presented in the video.

@@Mythago314 armchair physicist doesn't understand even the basics and comes to lecture lol.

Well, it's not a solution. It's paraphrase of the original question: "which twin gets older?" Why? Because the length of the spacetime path IS the amount of time one "gets older by". We DEFINE "getting older" using the "true time" that passed for the observer in question (time that observer measures for himself). The true time is parametrization of the worldline (spacetime path) and its amount is the length of that worldline. Saying "the twin whose spacetime path is longer aged more" is THE SAME as saying "the twin who aged more aged more". Not the solution, just paraphrase.

@@pawemarsza9515 Very good point! So I rephrase the solution then. The solution to the twin paradox is not to try to find something outside of the spacetime paths that "breaks the symmetry" between the twins, like acceleration and so on. Suggesting something that seemingly "breaks the symmetry" in one setup will be false in another setup. As you point out all that matters is which twin has the longer spacetime path in each case. Period. But you still see a problem with this? You still think we need to find something outside of spacetime paths that "breaks the symmetry"? Why?

@@nickergodos1554 both bob and alice can get the same spacetime distance in the original paradox relative to eachother, why does the twins who accelerates perspective get chosen?

@@nickergodos1554 I don't see any problem. The only true solution to twin paradox is "there is no paradox". If we are given external information (curvature of spacetime) we can easily calculate proper time for each twin. If we don't have that information, we can only measure their clocks after they ended their journey. That's it, nothing paradoxical.

I'd be inclined to listen to you if you can tell me how much space you are travelling through while you are standing stationary in one spot?

That's an excellent and apt question, which goes to the heart of the issue, consequently it deserves a full and sufficient answer. So first off: if as described in your example, B sees a notepad accelerate, the only empirical deduction he can make is that the notepad has accelerated with respect to him. Acceleration, as you say, only fundamentally measures rate of change of a relative velocity. Now, to reach the absolute quantity that you describe, the invariant "absolute acceleration" so-to-speak, the observer has to make a further deduction: he has to assume that his accelerometer has been already calibrated in an inertial frame. In this case of your notepad, this calibration stems from the observers familiarity with the workings of notepads on earth; i.e. the observers knows confidently that a notepad isn't going to be magnetically attracted to objects outside the plane, or exhibit any other internal forces of motion that would suddenly propel it towards the wall. But this knowledge about the notepad isn't contained within the system itself; it stems from familiarity with the workings of the notepad in larger contexts. An analogy would be stepping onto a scale to determine whether you're overweight or not. If the scale hasn't been properly calibrated, the reading it gives you won't yield any useful information about whether you are overweight or not. Only if you are certain the scale has been priorly calibrated via the use of a known weight, can you be certain that the measure of your weight will be accurately reflected. Thus the reading on the scale is a relative measure: it only tells you the difference of weight between you and the measuring instrument. But you need a second piece of knowledge -- knowledge that the scale has already been calibrated with a prior-known weight, before you can come to the conclusion that the reading on the scale is your actual or "absolute" weight. This is essentially the argument of our video "Do Inertial Frames Resolve the Twin Paradox?" So what is the absolute property that identifies the asymmetry of the paradox? Your guess is still as good as ours. Our current theories of relativity certainly do not account for it.

Acceleration, is misleading. In truth, you are constantly in motion with a fixed magnitude of motion, all while present within the 4D space-time environment. So, picture yourself being within a black room that is present within a spaceship. You are sitting in a chair that is pointing toward the left side of the spaceship. However, you have assumed that the seat points toward the front of the space ship, due to you being completely unaware that the black room had been slowly rotated to its current orientation. When the spaceship suddenly turns to the left, you feel yourself being compressed into the chair, and thus you assume that the spaceship is accelerating, even though it has simply changed its direction of travel. If it then turns to the right, your body is forced forward, and you now think that the spaceship is slowing down. So you have to understand that if you are in your car and you hit the accelerator peddle, in truth you have hit the change in direction of travel peddle. The same applies to the brake peddle. Your car is still in motion with space-time just as much as previously. All you have done when pressing these peddles is change its direction of the cars travel.

Depends on whether there is gravity and on the reference. Without gravity, circular motion is acceleration. But any geo-stationary satellite is the same as "free fall".

There's certainly a correlation between jumping frames and shorter spacetime paths in flat-spacetime, but in curved spacetime we see that correlation vanish, which of course tells us that jumping frames cannot be the fundamental agent of asymmetry.

My clock changes twice a year and my watch always run late. And my travelling twin is always paradoxing away from me. How come?

​@@eugenkellerget yourself a sundial. The most accurate measuring device in the universe.

So it's the number of degrees, which can be measured, as that solves the mystery of centrifugal force as well.

Okay, I talked to someone else in another comment and determined that the Doppler effect induced into the light being emitted would be impossible to detect using a detector on Earth because the detector would be traveling at the same speed. So, in a way, it would be like two trains traveling at the same speed some distance apart on the same track. If either sounded their horns, they would sound normal to the other train. So, while the movement of one the rear train compressed the sound waves moving forward from it, the fact that the ears of the people on the front train are moving at the same speed decompresses the sound wave, as it is moving towards their ears more slowly. I instead devised a different way that to detect the fixed position of the constant. If both trains agree to blast their horns at the exact same time, the rear train will hear the other's horn more quickly than the front train. This would be because the the distance the sound from the front train towards the rear train would be shorter than the sound going in the opposite direction. So, in the same way, light could reveal a fixed point in space. Put a set up satallites up in space with coordinated timers. Each will have a laser emitter and a laser detector and will fire their lasers at the other at precisely the same moment. Each will also be in fixed positions in relation to the other. They will then count how long it takes the light for the other one to reach them. If the satellites are moving along the axis they sit on, then one satellite should get the opposing satellites signal in a shorter time than the other. Note, this absolutely does not work if a single laser is reflected. Also, there will be no phase variance detectable or Doppler effect noticable. The only detectable trait would be the initial travel time and possibly the end time. From the lights perspective, they would be traveling from equidistant points and so there would be no difference to them in travel time to the points where the other was emitted from. It's the detectors that change position over time, one racing towards a laser and another racing away from the other laser. It may be fractional, but the one racing towards will narrow the distance while the one racing away will widen the distance. If light truly is a constant speed, then the travel times would have to be different. If both have exactly the same travel times, that to me would be definitive proof that the emitters added their respective speeds to the speed of their photons and thus light couldn't have a constant speed If the times were different though, the time gap could then be used to calculate the fixed point in space where the lasers emitted the light from and how fast the salellites moved away from those points, thus giving us a definite fixed speed relative to only a fixed point in space. Basically, I can't see how anything can be called a constant without fixed no relative positions in space existing. Otherwise they can't be constants. I have another person insisting a that the laser would always travel both ways in the same time and light still would have a constant speed. But then, that would mean that if we then shone that light to another galaxy, because that galaxy is moving at a different speed and direction compared to us, that our light wouldn't be traveling at the speed of light from that galaxy's perspective. It just doesn't add up. We know we're moving at a pretty good speed in space, because our solar system is orbiting our galaxy quite quickly, with respects to our personal measure of what quick is. We know our movement can't be added or subtracted from lights constant speed. So any detectors we have would be moving as well, and just like with the trains, they should offset making contact with light because of their movement in relation to its constant speed. This is probably worded poorly, but you should get the point.

@@haddow777 " _Put a set up satallites up in space with coordinated timers. Each will have a laser emitter and a laser detector and will fire their lasers at the other at precisely the same moment. Each will also be in fixed positions in relation to the other. They will then count how long it takes the light for the other one to reach them. If the satellites are moving along the axis they sit on, then one satellite should get the opposing satellites signal in a shorter time than the other_ " in the frame in which they are moving this will be the case. but in the frame in which they are stationary ,both satellites would get the opposing one's signal simultaneously " _Basically, I can't see how anything can be called a constant without fixed no relative positions in space existing. Otherwise they can't be constants._ " Speed of light is called a constant, because in every frame, its speed is c. You dont need any fixed positions in space.

@@riverchess-so7pr I get why you say that, but unfortunately, I don't think you can claim it as reality. Yes, the books all claim it is true, based on the Michelson-Morley experiment. The reality is that the Aether experiment (less typing) was seriously flawed and was designed to prove only one way that light could be affected by motion, but not all ways. So, while the experiment failed to prove what they personally thought was how light travelled, that failure does not prove that light is a constant from all frames of reference. Their idea of how light travelled was through a substance called Aether, and in their minds, a photon was like a boat on water. Now, if this was the case and the Earth was moving through this water, they felt that the relative motion would be like the Aether was flowing through the Earth. So, any photons fired into this flow would have to fight the current to make progress. Any photons fired perpendicular would similarly have to fight the current to maintain their direction. The machine was specifically designed to find these struggles the light would have had to go through, most specifically, the perpendicular path. They understood that the photons heading straight against the Aether, fighting against the current, would eventually turn back and catch a ride with the current. So any losses in time they made going one way would be made up with gains on the way back. The perpendicular route though, would in a way, be traveling through the Aether in an angular fashion to maintain their path. So, from an outside observer's perspective, its journey from the spitter mirror to the mirror and back would take a triangular path through the Aether rather than just a back and forth straight path. This would mean those photons traveled longer distances than the ones in the beam that went straight. So, they would be out of phase. So yes, their machine proved that line of understanding was incorrect. Here is another way to look at it through, that their machine never took into account, and therefore could never give any valuable data on. When a train is sitting still and sounds its horn, let's say an observer on the ground is standing far enough away to hear the sound in 5 seconds. Now, if the train passes that spot doing any speed, if they sound their horn at exactly the same spot, the observer will still hear it precisely 5 seconds later. It doesn't even matter which direction the train is travelling. This is because once the sound is created, it becomes completely detached from the train and any speed its moving. Chances are, if the train is moving fast enough, it won't even be near the location when the observer hears the sound. This is because the sound is travelling from the fixed point in space it was created at. This could be applied to light as well. Let's repeat the Aether experiment with this in mind. First, let's make the assumption that the whole beam is emitted from the left and the detector is closer to us. Also, let's assume that Earth's motion is in line with the initial beam and in the same direction as well. So, in the old experiment, they would have claimed the Aether was flowing towards the light source. So, right off the bat, the whole beam is heading towards the splitter mirror from the fixed point in space the photons making it up were created. Now, it isn't being slowed by any flow of Aether, what is actually happening is the experiment is moving away from the photons. So, while they are heading towards the splitter mirror at the speed of light, the mirror is moving away from them, creating more distance for them to travel to get to it. When they do, they are split as expected. Now, the beam going forward is also chasing a mirror moving away from it, so it will be traveling a longer distance to get to it too. Once reflected back though, now it is heading towards a splitter mirror that is heading towards it, shortening the distance between them. Since the mirror is traveling at the same speed as the other mirror, it erases any losses the beam had before. So, in effect, the return trip of this beam could be calculated like this, Xnew=((x+d)+(x-d))/2, or Xnew=x. Since all you get with a round trip like this is the average of both trips and both trips are different by the exact same amount, an average will only ever result in the same distance traveled. In any event, that isn't the important part right now. The perpendicular beam will head at a 90 degree angle to the beam that went straight. Now, unlike what they thought at the time, there is nothing moving the beam sideways, so it moves in a completely straight line. What really happens is the mirror it is traveling towards is moving sideways. Since this in no way alters the distance the beam travels, it has zero effect on the beams travel time. The same happens when it travels back. The detector is moving sideways too, but again, no change in distance, so when the beams combine, the phase is in line. In fact, under these conditions, they frequencies will always be in line no matter how the Earth's motion alter's the photon's travel paths. It literally cannot do anything else, so from this perspective, the experiment is highly flawed and could never provide useful results unless light actually flowed through a substance like the Aether they thought existed. So, in reality, your claims my experiment with the satellites wouldn't work as I described is completely unfounded. Also, yes, I know that the way I described the experiment working would create a drift between the beams. If we were looking at the experiment from the back side of the detector, the perpendicular beam would be slightly to the left and the straight beam would be slightly to the right. This still would not have any effect on the frequencies lining up, because the travel distances would be the same no matter what. Plus, the misalignment would be off by nanometers to possibly one or two micrometers, depending on the length the light had to travel after being split and also depending on the absolute velocity of the Earth relative to the fixed position in space the photons fired from. I don't think at the time they could have even measured a horizontal misalignment by that amount. If the Earth was moving some significant portion of the speed of light or the mirrors were a few thousand kilometers away, all that would happen is eventually the light would miss the mirror or the detector by being off to the side of it. It still wouldn't affect the phase of the frequencies, because even at those speeds the light would be traveling the same distances, not that they would be able to measure them against each other anymore.

Simple physics. Newton's Law of Motion. F=ma. Less acceleration equals either more mass or less force. This is going to come as a shock but its nor reported anywhere. And I mean anywhere. CLOCKS IN MOTION USE THE SAME AMOUNT OF ENERGY(FORCE) AS STATIONARY CLOCKS. Why the difference in clock cycles? That energy went into the extra distance traveled. CLOCKS MEASURE MOTION IN SPACE. NOT MOTION IN TIME. Tree ring growth patterns? Are they caused by changes in gravity, Earth's rotational speed, or sunlight (energy) from the sun? An astronaut's heart rate is in an accelerated heart rate during lift-off while the onboard clock is registering fewer click cycles. Why? Doesn't Relativity dictate that biological processes slow down with mechanical processes? Why do atomic clocks slow down? Simply from redshifting of the electromagnetic wave that accelerates the atom to the 9B oscillation rate. FORCE DECREASES WITH DISTANCE. in order to maintain the same amount of Force at the target with an increase in distance, the Force emanating from the source must also be increased. GPS clocks run at a different frequency (force) to account for the difference in distance traveled. Build a clock that can identify a change in force and automatically increase it, and you have a device that is in sync with your ground station.

The twins thoughts: "Why the heck not." Since the universe is doomed, because of the twin paradox.

It is incorrect to assert that the spaceships travel equal distances on the spacetime manifold. When the twins are reunited at a coincident place in time and space, one of them will have traveled a greater spacetime path than the other. This twin will be the older one.

@@dialectphilosophy Every object that exists within space-time, is in motion exactly as much as are photons of light in motion. That is the path taken by all photons. If one of two spaceships was truly at rest in space, then all of its motion would now be across the dimension of time. That would be its path of motion. First let's say that it remained on this path for 2 seconds. Meanwhile, the other spaceship at the beginning of those 2 seconds, decided to take a different path. Instead, it went off to the left at a certain velocity, and then returned around to head on back to the first spaceship, and all of this was completed in the very same 2 seconds. Due to both being in motion to the exact same degree, and doing so within a 4D space-time environment, both would have covered the very same distance within that 4D environment. The only difference is that one chose to dedicate all of its motion to being motion across the dimension of time, while the other did not. The other moved less across time due to setting its path to include a measure of motion across space.

​@@new-knowledge8040 You are conflating spacetime “distance” with spacetime “motion.” You are correct in asserting that, in the theory of relativity, everything travels at the speed of light, i.e., that the tangent four-vector to the path traveled by an object on the spacetime manifold (ds/dτ) has magnitude c. However, you have asserted that if two spaceships move apart and then come back together again, they have traveled equal distances on the spacetime manifold. This is not correct. (The twin paradox in fact relies on the twins having traveled unequal distances on the spacetime manifold, as we explain in our video.) Distance on the spacetime manifold is defined as ∫ds, or ∫ (ds/dτ)dτ, or ∫cdτ, so in fact distance on the spacetime manifold is essentially the product of the four-velocity c and the proper time elapsed as measured by a clock moving in that frame. Since the spaceships do not inhabit the same frame, their clocks will show different amounts of proper time, meaning they traveled different spacetime distances. (If distance = rate * time, you have to remember that although the rate of the two spaceships moving along on the 4-d manifold is the same, the time registered on their clocks is NOT.) General Relativity can be very subtle and complex sometimes, we understand the source of your confusion.

@@dialectphilosophy And I understand the source of your confusion.

In Einsteinian relativity, speed through spacetime is equal for everyone. This means that the distance covered and time elapsed can be adjusted accordingly!

There is no answer. Acceleration is just not relative, anyone who understands GR enough knows this.

So I watched @physicsgirl's video on this. She doesn't attribute the aging difference to acceleration. Instead, she states that the twin is "no longer in an inertial reference frame" when she accelerates, so SR can't be applied by treating both twins' frames equally. In other words, the apparent paradox arises from trying to treat the space traveler's path as inertial when it isn't. Acceleration only rules out that particular treatment, it doesn't cause differential aging. She goes on to describe the treatment of applying the principle of equivalence and the *GR* prediction of clocks slowing in a gravitational well. It's not the only approach, but it works in the problem regime. Since the problem involves instantaneous change of velocity, we can model it as a change over a short interval, and take the limit as we increase acceleration while decreasing the interval towards zero. She's not wrong.

Your explaination assumes as know which observer is inertial, which we do not

Thanks for watching! We will return to the twin paradox series next year... there are a few issues that stand in our way still and so our next videos will be tackling those first. With regards to your idea of absolute rest, a sort of related idea is that there is a minimum possible acceleration standard by which the gravitational force can effect objects. This ideas produces the results of MOND gravity, one of the dark matter theories.

@@dialectphilosophy MOND gravity isn't a dark matter theory; it's a tweak to gravity that obviates the need for dark matter theories. I believe it is also in the middle of a process of falsification, there being star clusters showing no Keplerian/Newtonian orbital aberrations that MOND would necessarily entail (and that DM theories would not).

@@-danR We weren't advocating for MOND, just pointing out one of the ways you can derive it. There's a multitude of issues with MOND that have been known for a while now; despite this some physicists push for it. We certainly can't claim to be experts in the subject matter.

@@renedekker9806 I think you missed the point. Einstein was originally going to call his theory something like the Theory of Invariance because the speed of light is constant in all reference frames and if I remember correctly was only called relativity because someone talked him into believing it being a catchier name, probably rightly so. The speed of light is absolutely something that is not relative to latch onto. It's everything else that is relative, light in a vacuum is constant and is noted as one of the constants of the universe. That speed has also shown to be true for gravitational waves experimentally recently so we can take light out of the equation simply say that the fastest anything can propagate in the universe, i.e. causality, is this constant.