Time dilation
Time dilation will cause a lot of problems for mankind when we're able to interstellar travel. Let's say in 2200 we find ourselves advanced enough to plan a visit to a new star system. Those people that leave earth for this trip will never see anyone they know from earth again due to time dilation. They will leave for a 50 year trip (for example) and hundreds and hundreds of years could have past here on earth, because of the time dilation their clock will move slower than ours due to the speed at which they would be traveling.
What this means for us on earth is that we won't learn anything from this mission to a new star system because they won't return before we die of old age, the next generation will gain the knowledge. Scientists will have to invest in these missions so that the people in few hundred years benefit from the exploration of a new star system.
The people who left for this mission will have only lived an extra 20 years and so if they return to earth the trip back would also add the amount of years onto earth, they would have essentially traveled to a future earth. Space missions are about to get very complicated.
What this means for us on earth is that we won't learn anything from this mission to a new star system because they won't return before we die of old age, the next generation will gain the knowledge. Scientists will have to invest in these missions so that the people in few hundred years benefit from the exploration of a new star system.
The people who left for this mission will have only lived an extra 20 years and so if they return to earth the trip back would also add the amount of years onto earth, they would have essentially traveled to a future earth. Space missions are about to get very complicated.
Comments (93)
They already are, but don't worry about it. Mankind will not be leaving the solar system in your lifetime.
Not necessarily. Because of Special Theory of Relativity's Receprocity one can say that Earth is accelerating away from the spaceship, so it is the clocks in the Earth that are slowing down.
Quoting RichEarth does not accelerate away. That would require a massive force on Earth, sending it out of the solar system.
Reciprocity of Special Relativity says there is no privileged frame of reference. If there is a privileged frame of reference, STR is wrong and Einstein's T is wrong. There is no T in GTR.
Earth might be moving away from the ship, but it is not ever accelerating away from it.
There is no privileged frame of reference under STR? Either viewpoint is coherent according to STR. STR doesn't allow for exceptions when it is convenient for a science fiction story.
You don't understand STR and GTR. There is no T in GTR and STR, which has a T, states all frames of reference are equivalent. Sci Fi adherents love to mix up and intermix the two. Makes Relativity so much more fun.
The Earth is not accelerating? Are you sure about this?
How does someone on the Earth know that they are not accelerating from the spaceship?
Where is the evidence that either equation is ontological and describes biological time/aging?
Where is T in GTR?
As I said, this stuff is great for Sci Fi programming but STR are about measurements and gravity not about biological aging.
Special relativity only applies to inertial frames of reference - those that are not accelerating relative to each other. Non-inertial frames, those that are accelerating, are covered under general relativity. This is something that has confused me. I've looked for explanations but different people who seem to know what they are talking about seem to have different stories. What follows is my understanding of what happens. I may have it wrong.
If two space ships travelling a significant fraction of the speed of light (c), but not accelerating, pass each other going opposite directions and check each other's clocks, each will observe that the other's clock has slowed down.
If, on the other hand, there are two space ships at rest relative to each other and one accelerates away from the other up to a significant fraction of c then turns around and comes back and then the clocks are checked, both will observe that less time has passed on the accelerating ship.
This is called the "clock problem" or "twin paradox." Look Twin Paradox up on Wikipedia and you'll see the kind of unsatisfying explanation I was talking about. Please don't think I think that "unsatisfying" is the same as "wrong."
And where does such a condition exist in the universe?
Quoting T Clark
Clocks may be affected by acceleration (but which one?), but this has nothing to do with biological aging. In any case, there had to be deceleration somewhere to even check the clocks.
I also want to underscore there is no T in GTR. Only some strange variable that is called space time because the equations entangle the two concepts. However, there is no reason to elevate the equations to an ontologically status since it is about measurement and not biological evolution.
Yes, I'm sure the earth is not accelerating. F = ma. If no force is applied, there is no acceleration. The force is applied to the spaceship, not the earth. You know what acceleration feels like. You are pushed back against your car seat. If you don't feel the push, you ain't acceleratin. No force will be applied to the Earth.
The Earth is accelerating. It is always accelerating (remember gravity?).
How does an observer who is measuring know what is accelerating. You are using information that is not contained in GTR. In GTR you are taking measurements. That is all. A person in a spaceship could just as easily claim the Earth is accelerating away via use of instruments.
Two cars sitting at a stop light next to each other are in an inertial frame of reference. Two cars travelling at constant speed and passing each other in a straight line going opposite directions are in an inertial frame of reference. You are in an inertial frame of reference with anything that is not moving in relation to you.
Quoting Rich
After Ship 1 accelerates away, turns around, and then returns, people on both Ships 1 and 2 will agree that the clock on Ship 1 is behind that on Ship 2.
Quoting Rich
That's not correct. The physical and chemical processes in our bodies are affected the same way as the processes in the clock.
Quoting Rich
Why is that? We can just get on the radio and ask what time it is.
Fixing the quote. I didn't say the 'Rich' part above.
More or less, yes.
I don't think relativity goes into explaining why our universe has this geometry. It just does, and the theory predicts what will be measured.
Quoting RichThe guy in the ship is plastered into his seat when doing the massive acceleration. The guy on Earth is not. OK, a black-hole sort of gravitational field could do that to Earth, but there is none in the scenario discussed.
Quoting RichTrival acceleration to non-relativistic speeds that cancel out over a year. See the part about the wobble around the sun I posted above.
The guy in the ship needs special technology to not die from the massive acceleration needed to get him up to enough speed to notice his age discrepancy, and he needs to do it 4 times (out, stop, start back, stop at end) before he dies of old age. The experiment is not practical even if we had a ship that could do that.
Quoting RichClocks can be unambigously compared when in each other's presence, and need not be stationary relative to each other. In short, you can look at each other as you pass by at speed if you like.
Quoting T ClarkSee above. Comparisons of spatially separated clocks are ambiguous and yield different answers depending on the reference frame chosen. The radio doesn't help. This ambiguous ordering is the best explanation of the twins experiment.
I had put together an illustration of the twins experiment which kept things quite simple, involves no acceleration (using instead a tag team), and thus no GR complications. I can post it again if you like.
Well, yes, the Earth is always accelerating - it is revolving around the sun, which involves acceleration. The whole solar system is revolving around the center of the galaxy, which involves acceleration. I don't see how that is relevant. The space ship moves away from the Earth at a faster and faster speed but no force has been applied to the Earth to make that happen.
Thought experiment. Two cars are next to each other at a stop light, not moving. The light changes and one of them accelerates while the other stays still. They begin to move in relation to each other. Let's say I put a small camera in each car to record what is happening while this is going on. If, later, I showed you the two films, would you be able to tell who was accelerating? Answer - yes. You would see the people in the accelerating car pushed back into their car seats. You would see the cup of coffee spill. You would see the little pine tree hanging from the mirror swing.
What's the "less" part?
They only get one peek at each other's clocks as they pass. You can't observe the dilation. If you're watching a moving clock, it appears to run faster if it is approaching. The Doppler effect is far more significant than the dilation.
If you want to get picky, the Earth revolves about its axis, not the sun. It orbits the sun.
I think this is not correct. Why do I only get one peek? Let's say the clock on the ship is constructed to flash a light at an established frequency. I can just measure the times between flashes as it passes.
Quoting noAxioms
I love being picky. It is appropriate to say that he Earth revolves around the sun. In the definition of revolve I looked up, it was one of the examples used. It would also be appropriate to say the Earth revolves around it's axis, but I would probably use "rotate."
If you want to get picky, the Earth revolves about its axis, not the sun. It orbits the sun.
— noAxioms
Fair enough. I got this from http://wikidiff.com/revolve/orbit:
I'm far from an expert when it comes to time and relativity, but I don't see how this makes any sense. The Earth and the spaceship aren't two isolated objects in a void, this is the real world we're talking about. When one thing moves, it moves relative to everything else in the universe. So when the spaceship accelerates, you could not say instead that the Earth is accelerating because the Earth isn't accelerating relative to the universe--only the spaceship is.
I'm thinking about this and I'm not sure. Why would the rate of flashing be different when it is approaching vs. moving away from me? The only difference I can see is that, as it gets closer to me, the angle between my line of sight and the direction of travel increases.
This is Doppler effect, the same reason a train horn pitch is higher when approaching. The effect is far greater at a given point of observation than that of time dilation.
Suppose we flash once a minute. Sun is 9 minutes away, and the flash source is coming at us at half lightspeed. The trip takes 18 minutes, but only 9 minutes to the Earth observer since the first flash is delayed by the 9 light-minute distance.
Time dilation might take one of those flashes off (I'm guessing), so you count 17 flashes in 9 minutes.
Still don't understand. This should have nothing to do with Doppler. That changes the wavelength of the light but won't change the frequency of the flash.
Without relativity, the trip takes 18 minutes, so the Earth observer sees 180 flashes in 9 minutes, twice the actual rate. Relativity says the fast-moving clock is dilated and only flashes 156 times (my guess was off) in those 18 Earth minutes. Still appears faster to the Earth observer. At 0.5c, the Doppler effect doubles the pace, and relativity removes only about a sixth of the pace.
Pretty sure this is wrong. Doppler changes wavelength/frequency of light. Relativity changes rate of time. Unrelated.
Does the half-lightspeed pulse generator not take 18 minutes (in Earth frame) to travel 9 light minutes? Does the first pulse not take 9 minutes to be seen, and the last not get seen immediately? What part isn't clear?
The twin paradox that was alluded to earlier arises when one neglects that the traveler twin can't be considered at rest in one single inertial frame of reference if she is going to eventually turn around and come back to Earth. The situation must therefore be analysed with respect to at least three frames of reference: one in which the Earth (and the twin remaining at home) remains at rest at all times, a second one in which the traveling twin is at rest during the outward journey, and a third one in which she is at rest during the returning journey. (We can imagine, for simplicity, that the acceleration period when the travelling twin reverses course is very short).
Considering the mutual Lorentz transformations of time and space coordinates between those three frames of reference solves the paradox through highlighting the asymmetry between the situations of the two twins. The traveling twin must effectively "jump" from one frame of reference to another one between the two legs of her trip, and at that time (as measured by her local clock) the definition of simultaneity with the corresponding time on Earth shifts. This shift accounts for the fact that her local clock marks a shorter duration than the clock on Earth over the duration of the whole trip in spite of the fact that, as referred to her own reference frames (on both legs of the trip) less time elapse on Earth that does on the ship on each separate leg of the trip.
Which one is slowing down? The sun or the Earth. Which is accelerating relative to the other.
I understand this time dilation stuff had been around for a long time and tickles the fancy of people who enjoy the Sci Fi aspect, but it is so full of holes in so many respects. The reason there is isn't more analysis of the problem is because it had no practical relevance so the fantasy story continues.
What is important is the t time in STR is not the t in GTR. There is no t in GTR.
Effects on acceleration on clocks and measurements had nothing to do with the biological sense of time and duration passing. This is a huge confusion.
As for acceleration itself, the equations do not provide and means for establishing what is accelerating. I am accelerating as I write this but I don't feel it. Feeling acceleration is not part of the equations.
Anyone who is interested in this question is going to have to do a ton of research but I am convinced it is a Sci Fi story, no more.
Nothing more to say.
we will make the spacecraft with propulsion. it is needed in order for the spacecraft to leave earth. when you create something with the intention of acceleration then it will accelerate. yes i understand that from each viewpoint both seem to be moving away from each other but the spacecraft has been built in order to accelerate. the only acceleration that earth is experiencing is its orbit around the sun and that wont change when the spacecraft leaves.
Two measurements, and from each point of view, something is accelerating.
How we ever got from a theory about gravitation to two vilification entities aging at different rates, I have no idea. It would be a great research project to find out who started this all. I know why it it to perpetuated. It sells books just like Black Holes.
your acceleration point still doesn't make sense.
Quoting Rich
yes that something is the machine that has been built to accelerate. if you dismiss the idea of having your own perspective of time depending on gravity and velocity, then why aren't you so quick to dismiss having your own perceptive of acceleration.
Look at the equation.
Do you feel propulsion when sleeping? You are still accelerating.
The force on Earth is primarily the weak gravitational fields of the moon and sun, which actually cancel out over a month/year respectively. Net vector of almost zero. The space craft has much greater acceleration due to orders-of-magnitude greater force to mass ratio, and it is applied in a consistent vector (at least until mid-trip where it turns around), unlike the gravity.
You describe the ship/earth as symmetrical cases, each moving away from the other's point of view, but that isn't acceleration. If it was a symmetrical situation, one twin would not be older when they are reunited. The difference is acceleration, or more precisely, the moment of acceleration. Both twins can accelerate equally (for control purposes if you like), but the one with the greater moment will be younger when the reunite.
That's right. It has to do with knowing what acceleration is.
You're confusing it with velocity. Yes, in the frame of the fast moving ship, Earth has the high velocity, but from any point of view, it is the ship, or the frame of the ship, that does the significant accelerating.
Just throwing GTR term around or labeling as science fiction the description of others isn't helping.
Gravity plays a trivial role in the scenario being discussed. We're not computing it to 7+ digits here. You only need to do that if you're actually writing the navigation software that needs to get the ship to its target.
GTR has zero relevance to biological systems. It's about the problems of measurement. Every body in the Universe is accelerating. There is no privileged frame of reference. There is no t in GTR. It is some manufactured space-time thing. End of story.
There isn't a problem with measurement. Precisely-measured differences in clock tick rates have been observed that are consistent with the predictions of special and general relativity.
Quoting The Hafele–Keating experiment
The problem was and continues to be determining simultaneity. This was the root issue. The answer that was present by STR is bizarre. There is a privilege reference frame. It is the one where the train is hitting the car. But I don't want to get into all of the messiness of Relativity. Einstein didn't receive a Nobel prize for it and for good reason. He actually tried to elevate it to ontology for heaven sakes. Clocks do not measure human biological aging (real time), they measure space traversal with the purpose to establish order tsimultaneity - a completely different story. The sci fi book writers who wrote about relatively are way ahead of themselves.
Actually, I remember reading that Einstein had come to have some misgivings about his theory being named "Theory of Relativity". He thought this was unfortunate and had a tendency to give rise to misleading interpretations. That's because there is much more of an emphasis, in the so-called theory of "relativity", about *invariants*. The speed of light, for instance, in an invariant. Spatial distances between events, or the speeds of point particles, already had been regarded to be relative to a frame of reference in the framework of classical mechanics, but the frame relativity of (instantaneous) distance, duration, and simultaneity all are direct consequences of the invariant geometry of Lorentzian space-time (in special relativity) and of the invariant intrinsic curvature of space-time represented by the metric tensor (in general relativity).
When Rich says that there it no 't' in GR, I think he means to say that there is no time dependence of the invariant structure of the metric tensor (that is, of the geometry of space-time). That is true in a sense. It's just because space-time incorporates the temporal dimension and hence does not, as a whole, have a variable geometry as a function of time. This would just not make sense since there isn't a temporal dimension external to space-time. However, from an empirical standpoint, for finite creatures such a us who live in a particular moment in time and are interested in making predictions about the future (and explaining the past) the equations of General Relativity can be put to use operationally to factor out the time dimension relative to a specific local frame of reference relevant to us and predict how strong the gravitational field will be in each point of space relative to this specific frame of reference, and how it will vary as a function of time (as measured by local stationary clocks).
No. There's no such principle. The spaceship's engines are accelerating the spaceship, not the Earth.
Time dilation has been observed in various ways. It has been observed that less time transpired in the system that was accelerated to high speed, in comparison to an unaccelerated system. ...when their clocks were compared later.
Shouldn't we leave physics to the physicists?
We live in a culture in which science is important and highly valued. Therefore, there's a strong tendency to worship science. That's our culture's main religion now.
As for interstellar travel, if our civilization ever achieves fast interstellar travel, we'll probably have good enough robotic technology by then, that there won't be a need for humans to be on the starship.
The robotic probes will, by that time, be able to find out all that we want to know from visits to other solar-systems.
Of course it will take a long time, and so, as you said, it would have to be done as a longterm investment, (if at all).
I don't believe that just because something becomes technically possible it should be done.
Michael Ossipoff
You won't find "Spaceship engines" as a variable in any Relativity equations.
The rest is literally Sci Fi.
I'd said;
Rich says:
Quoting Rich
Regardless of what's accelerating the spaceship, it's being accelerated to (and then back from) high speed with respect to the Earth. It's the spaceship, and not the Earth that's being accelerated.
When an equation in physics includes a force or an acceleration, the equation doesn't typically specify or label the origin of the force, or the name of the thing that caused the force.
Rich says:
I would remind Rich that interstellar travel was the topic of the thread's original post.
Maybe a better example of science fiction is Rich's incredible mis-statements about physics.
Rich is referring to this:
Quoting Michael Ossipoff
Prominent computer scientists predict advances in robotics, on a timescale shorter than the timescale predicted by phyicists for feasible interstellar travel.
A long time ago, the radio astronomer, Bracewell, discussed the obvious likely eventual feasibility of robotic interstellar probes.
Physicists say that interstellar vehicles are still very far off. That statement, too, isn't science-fiction.
I continued:
Hardly a doubtful sci-fi suggestion, given the planetary probes that have recently been in use.
Even at near-relativistic speeds, it would take a long time to get results from interstellar probes.
Yes I was talking about something that couldn't be feasible and worthwhile to do for a long time. (Arthur Clarke has pointed out that any interstellar probe that could be sent any time soon would be passed-up by faster ones sent out later.)
I don't consider it at all certain that there will be any reason, or perceived reason, or motivation, to do interstellar travel, or probes, even when it becomes more feasible.
Michael Ossipoff
Or, a person on Earth could look at the spaceship and conclude that the Earth is accelerating away from the spaceship.
The distinction between uniform and accelerated motion, relating to why only the spaceship experiences time-dilation, and why its clocks read slow when compared to ours, is commonly discussed in typical articles on this subject.
Michael Ossipoff
Just check your facts before you post. It will result in a smoother and more peaceful discussion. You're getting aggressively-assertive, when you're mistaken. Surely you want to avoid that.
In general, it's best to stay civil.
Michael Ossipoff
No, I mean the force of the "Spaceship engines".
The spaceship person is in a coma.
Sorry, you can't stick spaceship engines in the equations. But I'll double check.
What equations are you talking about? Are you making any use at all of the Lorentz transformations (as you should?) In that case you surely should be aware that those equations apply to space and time coordinates as measured in *inertial* reference frames. The reference frame in which the Earth remains at rest and the reference frame in which the travelling rocket remains at rest can't both be inertial frames since there is a relative acceleration between them. So, you have to think again how you might be misusing the equations of special relativity to apply to accelerating reference frames.
So, you are making use of the equations of the General Theory of Relativity? Those equations are Einstein's field equations. They will tell you how to relate the metric tensor (that describes the geometry of space-time) to the stress-energy tensor (that describes the density and flux of energy and momentum in space-time). From this, is should appear that the people who remain on Earth have a space-time path that follows closely a space-time geodesic (and might follow it even more closely if they were orbiting the Earth in 'free fall' rather than resting on its surface) while the travelling twin follows a path that deviates very sharply from this geodesic (because of the rockets). When you integrate the proper-time along the space-time path of the traveler, you should find out that this proper-time is shorter than the time elapsed along the path followed by people who stay on Earth.
They don't because they're equations of physics and not biology. But they do tell you how much time will be elapsed on Earth, and on the ship, as measured by any clock that is governed by physical processes such as, say, an atomic clock or a clock based on local measurements of the travel time of a pulse of light. There is no reason, though, why there would be a mismatch between the rates of typical biological processes and the rates of the underlying physico-chemical processes that they normally are correlated with.
What I meant to say was just that modern physics--general relativity, quantum mechanics, etc. is really a complicated, involved specialized subject, and one best left to its specialists.
Only a physicist, or maybe someone advanced in a physics curriculum will know what's going on at the frontiers of physics, what those subjects are about. There's really no point in our debating those matters here.
Michael Ossipoff
After my previous post, I should emphasize that, though I don't know general relativity, I'm sure that many would agree that Pierre-Normand sounds like he knows what he's talking about. So I didn't mean to claim that no one here, or in this discussion, knows modern physics. .
I just meant that it's just a subject that few people are qualified in, even if a there are a few here who are.
Michael Ossipoff
.
A lot of scientists understandably believe that science explains everything. You can't blame them. They've mastered a very complicated and difficult subject, and it's natural to have a feeling that it's everything.
Certainly not all--but some--scientists are Scientificists (Science-Worshippers). Of course a lot of people who aren't scientists are Science-Worshippers too.
You, Rich, have accused me of being one (a Science-Worshlpper, not a scientist). I'm not. All Science-Worshippers are Materialists (aka "Naturalists". ...and sometimes "Nominalist" is used to mean effectively the same thing as "Materialist"). I'm not a Materialist. You've heard my metaphysics.
But where you, Rich, are making a mistake is to not accept that scientists are right about their own field,
I personally feel that Western academic philosophy is bullsh*t, but physicists and other scientists are experts in an objective and solid subject, even if a few take it outside its legitimate range of applicability and claim that the material world that they study is all of Reality.
Michael Ossipoff
Of course I can. They are subject to greed and over self-aggrandizing like any other human, maybe even more because the stakes are higher. It's not as it it is Determined that they should exaggerate by some Laws of Physics. They do it because of who they are. There are BS artists in every field, and the best get the most money and most advancement. That is the nature of industry. Money is what counts.
Sure, there are a small minority of scientists who have allowed themselves to be bought, and hired to say that there's no human-caused climate change. Likewise the cigarette companies never found a lack of purchasable scientists to publish favorable studies about cigarettes.
But those are the exceptions. Only a very tiny minority of scientists are on the industrial climate-denial payroll. Scientists are nearly entirely unanimous about the impendiing human-caused climate disaster.
Michael Ossipoff
There are many forms of exaggeration (even in the pop books) and most everyone just goes along with it because why put their neck out on the line. Anyone who protests is quickly ejected. No different than any profession where big money is at stake. Hear no evil, speak no evil, see no evil. Just pretend it's not happening.
Sometimes it seems to me that there's a bit of exaggeration of science's needs and goals. Though I'm not anti-science, I don't support everything science does.
I opposed the Large Hadron Collider (LHC). I oppose the Parker solar probe (It's scheduled to be launched this year). I oppose the Nazi-esque harmful medical experimentation and product-testing on live animals.
Michael Ossipoff
Time dilation is a real observable and measurable phenomena. Time dilation is seen in both special relativity (relative motion) and general relativity (gravity or acceleration) .
In fact the GPS system would be worthless were the effects of time dilation on the clocks in the satellites not taken into account. In this instance general relativity (gravity) effects dominate.
Depicts the time dilation as a function of orbital height relative to a stationary observer on earth. The total dilation is due to two distinct effects: Special relativity accounts for slowed time in orbit (relative to the observer on earth) depending on the orbital velocity associated to a specific orbital height. General Relativity accounts for accelerated time (relative to the observer on earth) due to the distance to the earths gravitational center. This depiction simplifies by assuming circular, equatorial orbits without inclination, upon which special relativity is weakly dependent.
All this says is that clocks are affected by gravity. I'm not surprised. But this has nothing to do with duration of life. This is what Bergson and others reject, i.e. that clock measurements have anything to do with experiences biological life. To make matters worse for Relativity, STAR head no place in reality and GTR had no place for very time (as we know it). However the kinds of leaps in imagination that science is well-known for. Scientists just get carried away. A few neurons moving and they discovered everything about mind.
You just made the same error of equivalence between physical process and the process of duration which by nature is continuous and heterogenous. Where in GTR are there explanations for the experience of duration as we are daydreaming or sleeping? The experience of living is not ruled by clock measurements.
This is an example of getting carried away and jumping to all kinds of assumptions. We create clocks to measure simultaneity and then all of a sudden, out of no where, our experience of existing depends on it. Not so fast.
As a matter of observation, the human body which is under constant acceleration, just lives. If placed under extreme forces it will die. As for the Mind, I don't know, but I do speculate.
There are several direct proofs of time dilation. Extremely accurate clocks have been flown on jet aircraft. When compared to identical clocks at rest, the difference found in their respective readings has confirmed Einstein's prediction. (The clock in motion shows a slightly slower passage of time than the one at rest.)
[i]In nature, subatomic particles called muons are created by cosmic ray interaction with the upper atmosphere. At rest, they disintegrate in about 2 x 10E-6 seconds and should not have time to reach the Earth's surface. Because they travel close to the speed of light, however, time dilation extends their life span as seen from Earth so they can be observed reaching the surface before they disintegrate.
Answered by: Paul Walorski, B.A., Part-time Physics Instructor
In October 1971, Hafele and Keating flew cesium-beam atomic clocks, initially synchronized with the atomic clock at the US Naval Observatory in Washington, D.C., around the world both eastward and westward. After each flight, they compared the time on the clocks in the aircraft to the time on the clock at the Observatory. Their experimental data agreed within error to the predicted effects of time dilation. Of course, the effects were quite small since the planes were flying nowhere near the speed of light.
Such time dilation has been repeatedly demonstrated, for instance by small disparities in a pair of atomic clocks after one of them is sent on a space trip, or by clocks on the Space Shuttle running slightly slower than reference clocks on Earth, or clocks on GPS and Galileo satellites running slightly faster.[1][3][4
• In 1959 Robert Pound and Glen A. Rebka measured the very slight gravitational red shift in the frequency of light emitted at a lower height, where Earth's gravitational field is relatively more intense. The results were within 10% of the predictions of general relativity. In 1964, Pound and J. L. Snider measured a result within 1% of the value predicted by gravitational time dilation.[31] (See Pound–Rebka experiment)
• In 2010 gravitational time dilation was measured at the earth's surface with a height difference of only one meter, using optical atomic clocks.[20]
• Hafele and Keating, in 1971, flew caesium atomic clocks east and west around the earth in commercial airliners, to compare the elapsed time against that of a clock that remained at the U.S. Naval Observatory. Two opposite effects came into play. The clocks were expected to age more quickly (show a larger elapsed time) than the reference clock, since they were in a higher (weaker) gravitational potential for most of the trip (c.f. Pound–Rebka experiment). But also, contrastingly, the moving clocks were expected to age more slowly because of the speed of their travel. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40±23 nanoseconds during the eastward trip and should have gained 275±21 nanoseconds during the westward trip. Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59±10 nanoseconds during the eastward trip and gained 273±7 nanoseconds during the westward trip (where the error bars represent standard deviation).[35] In 2005, the National Physical Laboratory in the United Kingdom reported their limited replication of this experiment.[36] The NPL experiment differed from the original in that the caesium clocks were sent on a shorter trip (London–Washington, D.C. return), but the clocks were more accurate. The reported results are within 4% of the predictions of relativity, within the uncertainty of the measurements.
• The Global Positioning System can be considered a continuously operating experiment in both special and general relativity. The in-orbit clocks are corrected for both special and general relativistic time dilation effects as described above, so that (as observed from the earth's surface) they run at the same rate as clocks on the surface of the Earth.[37][/i]
The time that clocks are measuring is not divorced from the physical process underlying the measurement. In fact time is just an abstraction from the underlying physical process and change. It is the physical process which is slowed and correspondingly chemical and biological process are slowed. Admittedly the conclusions arising from modern physics, relativity and quantum physics run counter to our everyday intuitive sense of space and time but nonetheless no more compelling theory to explain the evidence and observations is currently available and talking about Henri Bergson and his conception of "duration" just does not provide an explanation for the observed facts.
When they accelerate a person to the speed of light, let me know what happens.
What I object to it's flight of fantasies replacing actual observations. You keep substituting clocks for life. Gross misrepresentation of the experience of Life. Duration cases for me when I am unconscious, clocks keep ticking. BIG difference. Clock time is not life (real) time - the time of duration. Why all the substitution? Because science doesn't have the foggiest notion about the nature of Life, so it substitutes dead matter. That will get someone far.
Too much fantasy in science nowadays. Neurons are minds. Time is clocks. Drugs are healthy. What a mess.
About measuring dead things, that is all. Einstein (actually, it was probably his wife) used some crazy mathematics to describe the effects that gravity has on measurements and matter and thanks to some Sci Fi writers, bingo, bango, it becomes a new ontology about the nature time. How's that? It has zero to do with life and duration. Never was meant to, never will be. Time (the time we experience and feel) is not in any equation. That it is, is called flight of fantasy.
Life is the providence of itself, the experience of Life is that if the Observer, and substituting dead things or symbolics for the nature of Life will get someone no where except utter confusion. Zeno demonstrated this in a most amusing way.
If someone is accelerated, the physical life will die and I can only speculate what will happen to the mind. But whatever it does, it certainly will have nothing to do with ticking clocks.
There is the point of view that inevitable leads to fantastical conclusions as reached by over zealous readers of Relativity. What started out as some mathematics to explain compare and transform measurements becomes - without even a single breath of reelection - a full blown ontology. Welcome to the world of Sci Fi time travel. The Mind created mathematics, chemistry, physics, and all other sciences, not the other way around.
Duration is what we all experience as life. Forget the clocks. They are limited tools for attempting to establish simultaneity of events. Nothing more. People are so apt to get carried away but a good Sci Fi story. Stories are fun and easily contrived. Understanding life takes - a long, long time.
BTW, science as an industry, is about as far away from objectivity as anything can be. In anyway, case, objectivity if science is just another one of those myths for those who like to believe in objectivity.
Well, that is pretty silly. As silly as suggesting chemistry comes before mind. No matter that no one ever suggested this.
Time to start observing life as opposed to substituting stories?
Real life science demonstrated. This is how it is really done.