Speed of light what if question.

In summary: The disc has a circumference of 599,584,916 meters. The disc would be spun by a shaft with a diameter of say 19 meters. Then you space clocks at regular intervals in line with each other from the center of the disc to the outer edge. With another clock not attached, to be a control clock. Then you spin the shaft at 60 RPMs. Or one turn per second. So saying that nothing would fall apart. A clock placed at 9.5 meters out from the center of the disc. Would be traveling approximately 60 meters per second. (That is equal to the circumference of the disc at that point.) As you kept moving out each clock would be traveling
  • #1
UglyEd
31
0
Here is something I have thought about and would like to hear some other peoples opinions on what would happen if.
You had a huge disc in space. Made from an indestructable material that wouldn't bend or twist. The disc has a circumference of 599,584,916 meters. The disc would be spun by a shaft with a diameter of say 19 meters. Then you space clocks at regular intervals in line with each other from the center of the disc to the outer edge. With another clock not attached, to be a control clock. Then you spin the shaft at 60 RPMs. Or one turn per second. So saying that nothing would fall apart. A clock placed at 9.5 meters out from the center of the disc. Would be traveling approximately 60 meters per second. (That is equal to the circumference of the disc at that point.) As you kept moving out each clock would be traveling faster and faster than the ones before it. Then at about 4,771,351 meters out from the disc center the clock there would be spinning at the speed of light. (Traveling a circumference of 299,792,458 meters) The clock at the outer edge of the disc would be traveling 2x the speed of light.
Some things I know would happen are. Each clock although inline with each other would be in different space times. The disc itself would be in different space times from itself. From 4,771,351 out from the center and past that it would be going back in time. Right? Also the mass of the disc would increase from the center out. At 4,771,351 meters out from center and past that it would reach infinite mass? Would that mean that even though the shaft that spins the disc isn't moving that fast. 60 meters a second at its fastest point. It couldn't go that fast cause it would then be attached to a disc that after a certain point has an infinate mass? So the shaft would then have a speed limit of just under 30 rpms? (Which would mean that the outer edge of the disc would be traveling at just under the speed of light)
So even with the shaft having a max speed of just under 30 RPMs. The clock and the atoms at the outer edge of the disc would be barely moving through time, compared to the control clock (cause the would be moving just under the speed of light). Or to a clock and the atoms at the center of the disc. If the disc were to keep spinning. Say 100 yrs on the control clock. The atoms and the clock on the outer edge of the disc would be almost 100 years younger than the clock and the atoms at the center of the disc. So the same disc would exist both in the present (in relation to the static control clock) and nearly 100 yrs in the past?
 
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  • #2
I have another question to ask: does the retard time affect the speed of light?
 
  • #3
UglyEd said:
The disc has a circumference of 599,584,916 meters. The disc would be spun by a shaft with a diameter of say 19 meters. ... Then you spin the shaft at 60 RPMs. Or one turn per second. So saying that nothing would fall apart.

Wrong assumption from the beginning... Do you see why?

The inner part of the disk would have to break from the outer edge, otherwise you would need an infinite force (impossible) to pull the string.
 
  • #4
I was thinking more of it accelerating up to speed and turned by a motor. Also the whole thing being indestructable. Yes though it would take an impossible infinite force to turn it at 60 RPMs. What about the second part though. It could theoretically reach just under 30 RPMs. Which means none of it would pass the speed of light (just under at the outer edge) which means it wouldn't need an infinite force to spin it so theoretically possible. So at just under 30 RPMs what about the time thing with the outer clock barely moving in time compared to the clock in the center, or the control clock. The disc could theoretically exist in the present (control clock) and 100 yrs in the past (clock at outer edge)?
 
  • #5
UglyEd said:
Here is something I have thought about and would like to hear some other peoples opinions on what would happen if.
You had a huge disc in space. Made from an indestructable material that wouldn't bend or twist. The disc has a circumference of 599,584,916 meters. The disc would be spun by a shaft with a diameter of say 19 meters. Then you space clocks at regular intervals in line with each other from the center of the disc to the outer edge. With another clock not attached, to be a control clock. Then you spin the shaft at 60 RPMs. Or one turn per second. So saying that nothing would fall apart. A clock placed at 9.5 meters out from the center of the disc. Would be traveling approximately 60 meters per second. (That is equal to the circumference of the disc at that point.) As you kept moving out each clock would be traveling faster and faster than the ones before it. Then at about 4,771,351 meters out from the disc center the clock there would be spinning at the speed of light. (Traveling a circumference of 299,792,458 meters) The clock at the outer edge of the disc would be traveling 2x the speed of light.
Some things I know would happen are. Each clock although inline with each other would be in different space times. The disc itself would be in different space times from itself. From 4,771,351 out from the center and past that it would be going back in time. Right? Also the mass of the disc would increase from the center out. At 4,771,351 meters out from center and past that it would reach infinite mass? Would that mean that even though the shaft that spins the disc isn't moving that fast. 60 meters a second at its fastest point. It couldn't go that fast cause it would then be attached to a disc that after a certain point has an infinate mass? So the shaft would then have a speed limit of just under 30 rpms? (Which would mean that the outer edge of the disc would be traveling at just under the speed of light)
So even with the shaft having a max speed of just under 30 RPMs. The clock and the atoms at the outer edge of the disc would be barely moving through time, compared to the control clock (cause the would be moving just under the speed of light). Or to a clock and the atoms at the center of the disc. If the disc were to keep spinning. Say 100 yrs on the control clock. The atoms and the clock on the outer edge of the disc would be almost 100 years younger than the clock and the atoms at the center of the disc. So the same disc would exist both in the present (in relation to the static control clock) and nearly 100 yrs in the past?

You seem to have made a lot of inacurate assumptions, so we can "guess"the result but we cannot rely on our current equations to calculate something they are not meant to.

1. None of the clocks would be traveling at c or 2c. Even if you are traveling past me at .9c and I am traveling past you at .9c in the opposite, it does not mean that our velocities are 1.8c. Spacetime does not allow this.

2. Infinite force Well if we assumed that, we could assume a lot of things which relativity forbids.

Im just pointing out a few things, I like getting hypothetical over things to hehe
 
  • #6
1. None of the clocks would be traveling at c or 2c. Even if you are traveling past me at .9c and I am traveling past you at .9c in the opposite, it does not mean that our velocities are 1.8c. Spacetime does not allow this.

I think you misunderstood what I am saying. The clocks are all in line with each other. Each going further out on the disc, but they stay in line. Example: 1 Clock in the center of the disc 1 clock at 4meters out from center another at 100meters out etc.. With clocks spaced out all the way to the edge. With the disc spinning at just under 30 RPMs. The circumference of the disc is 599,584,916 meters so with almost 1 rotation every 2 seconds The farthest point on the edge of the disc where the last clock is would be moving nearly the speed of light. The clock at 4 meters out would be moving approx. 25 meters per second. (The circumference of the circle at 4 meters out from center.) So even though the clocks never pass each other and stay perfectly in line. They will be moving faster as you go out from the center cause they travel a greater distance with each rotation. Then cause the faster something moves the slower time moves. (relative to a stationary object) Compared to the stationary control clock. The clock at the outer edge would be barely moving through time. If you started all the clocks at say 12:00 on 1/1/2006. Then let the disc spin for 100 yrs ( on the stationary clock) The stationary clock would read 12:00 on 1/1/2106. The clock at the very edge cause it has been moving nearly the speed of light may only read 12:05 on 1/1/2006. Each clock from the center on out would show a lower date and time as the one before it. All the clocks although in line with each other and traveling the same RPMs. Would be moving at different speeds. Faster as you went out from the center. So wouldn't that mean that the disc would be 100 yrs old or so at the center and only 5 mins old at the edge? The same disc would exist in the present and 100 yrs in the past?


2. Infinite force Well if we assumed that, we could assume a lot of things which relativity forbids.

The infinite force would be the reason that the disc could only spin at just under 30 RPMS. That way no part of the disc would be spinning at the speed of light. Which causes infinite mass. It would need infinite force to move an infinit mass. My 1st question breaks laws of physics. The 2nd part though with the fastest point of the disc spinning just under the speed of light doesn't break any laws.
 
  • #7
..

lwymarie said:
I have another question to ask: does the retard time affect the speed of light?

how about my question.../.\
 
  • #8
UglyEd said:
So wouldn't that mean that the disc would be 100 yrs old or so at the center and only 5 mins old at the edge? The same disc would exist in the present and 100 yrs in the past?

The disk would be of various ages as you move outward, that much is correct (the center of the disc experiences 100yrs while the edge experinces only 5 min), But that does not mean that mean that the outer parts of the disc would "be in the Past".
 
  • #9
lwymarie said:
how about my question.../.\

The speed of light is the same for all inertial frames.
 
  • #10
The disk would be of various ages as you move outward, that much is correct (the center of the disc experiences 100yrs while the edge experinces only 5 min), But that does not mean that mean that the outer parts of the disc would "be in the Past".

What would that mean then for the RPMs and speed of the disc? The motor turning it is set to 29 RPMs. If you used the control clock or a clock at the center. In 100 years at 29 RPMs the disc would have made 1,524,240,000 rotations. According to the outer clock though it would have made that many rotations in 5 mins. Which would mean that it would have to be turning at a lot more RPMS so turning faster, but it is really turning at 29 RPMs. What would it be? Would that mean only a stationary clock is accurate?
 
  • #11
well i mean, if a light is near a gravity field, then the time will retard. Then we see the light traveling slower...
 
  • #12
lwymarie said:
well i mean, if a light is near a gravity field, then the time will retard. Then we see the light traveling slower...
do you mean time delation here? retarded time in relativity means the other thing...
Well, the answer is NO , However, in fact, the time delation affects the light in the other way. i.e. frequency... Have you heard about red shift? Can you use time delation in gravity field to explain it?
 
  • #13
What would that mean then for the RPMs and speed of the disc? The motor turning it is set to 29 RPMs. If you used the control clock or a clock at the center. In 100 years at 29 RPMs the disc would have made 1,524,240,000 rotations. According to the outer clock though it would have made that many rotations in 5 mins. Which would mean that it would have to be turning at a lot more RPMS so turning faster, but it is really turning at 29 RPMs. What would it be? Would that mean only a stationary clock is accurate?

If the above is true. Would that mean that there IS a constant time, but when something is moving it is avoiding the full passage of the constant time? There is a "constant time" it is just that different objects experience its passage at different rates?

Also would that mean if someone were able to stand on the outer clock. They would see 100 yrs of events happen in what would be to them 5 mins?

Or would it also mean that you could think of a "constant time" like a wave that moves at the speed of light. Then when an object moves the "constant time" waves don't pass the object at the same rate as a stationary object. Then if an object moves at the speed of light. It is like hoping on and riding a crest of the "constant time" wave. Therefore it it doesn't experience its passage at all?

Would it also mean that traveling into the future in a way IS possible. By moving at or near the speed of light or just moving at all. Cause by moving at the speed of light you are staying in the present time riding a "constant time" wave. Then say you do that for a "constant time" of 100 years. Then when you stop because some "constant time" has been steady moving at a constant rate. (Like the spinning disc has always been turning at 29 RPMs and turned 1,524,240,000 times in the 100 yrs that passed on the control clock. Only 5 mins passed on the outer edge clock, but the disc still turned 1,524,240,000 times at 29 RPMs, and the outer clock experienced it all in 5 mins ) You stop 100 yrs in the future, to you though it feels as no time has past?
 
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  • #14
While the hypothesis that started this thread is intriguing the effects that occur are so localized as to be meaningless. From center to edge there is a light wave length shift and that is about it. To an observer 10 million miles away relative to their point in space the disk is nothing of particular interest. The reflective light emanating from all points on the disk is a constant wavelength.

Furthermore you have not established two isolated points in the continuum. Since the disk is considered a single point theoretical applications do not apply. Again the post made one think but it has no applicable significance.
 
  • #15
Since the disk is considered a single point theoretical applications do not apply.

Why?

Wouldn't it be pretty much the same way they tested the theory that time does slow down when an object is moving. They used 2 atomic clocks one on the Earth the other in an airplane. After flying the plane for awhile the clock on the plane was slightly behind the clock on the ground.
The clock on the ground was moving with the Earth rotating. So was the plane just faster.

It is the same with the disc right? The outer clock is moving just under the speed of light. So time would have to slow down for it, just like the clock on the plane. Time would barely move on the outer clock compared to the center clock or an outside control clock. The motor would have made that many rotations in 100 yrs. It couldn't at 29 RPMs have done it in the time the outer clock would show. So the outer clock is inaccurate. The non- attached control clock, also the least moving would show the most accurate time. Time kept ticking (the disc kept turning) but the outer clock missed most of it.

Maybe in some ways it is like time is a river, and clocks (any object) measure time by how much water flows past them. If the clock is not moving, the maximum amount of water (time) flows past. Time passes for it at the fastest rate. Then the faster the clock moves with the current the less water passes it. So it counts time slower than when stationary. If the clock is moving at light speed (speed of the current) no water passes it therefore no time. The river though always flows at the same rate. The same way the disc kept spinning at 29 RPMs. So time would be constant? Objects just experience it at different rates?

If that were all true. Would it mean that if there were 2 twin objects created at the beginning of the universe. One of the objects never moved. The other forever moved at near light speed.

The stationary object would have experienced as much time as is possible in the universe. It would be as old and would have aged as long as the universe. If it were a clock it would show the true constant time.

The other, moving object even though created at the same time. (And would really be the same age. Around since the beginning.) It would have only experienced and aged a small amount of time. Basically a smaller amount of time would have passed it by or even happened for it. So just because it doesn't know it doesn't mean that time didnt keep moving. Time just didnt move past it as fast as possible.
 
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  • #16
Something rather similar exists in nature ... young pulsars such as that in the Crab Nebula. Particles trapped in the (intense) magnetic field of the pulsar move around it with the same period as the pulsar itself, ~30 ms in this case. What happens where the electrons (etc) are moving relativistically?
 
  • #17
The thought experiment is flawed. It assumes material properties that cannot and do not exist. A neutron star is the densest known state of matter in the universe, and it does not exhibit any such properties.
 
  • #18
Some pulsars (neutron stars) rotate with a period that would give a surface velocity of something like 0.7c if it was a rigid body. It is clearly possible to imagine something to rotate fast enough as to experience measurable relativistic effects.

The thought experiment is perfectly valid, that the disc edge is spinning at close to the speed of light is just a way to make things clear. The effects would arise at any speed and for any size of disc. A CD in a CD player would work just as fine.
 
  • #19
UglyEd all you say is correct but once again it is a closed system. So it is only relative to that particular environment. You are applying Macro Theories to the micro. If all that were true I could use a plate spinning on top of a stick and claim interdivisional displacement.
 
  • #20
Nereid said:
Something rather similar exists in nature ... young pulsars such as that in the Crab Nebula. Particles trapped in the (intense) magnetic field of the pulsar move around it with the same period as the pulsar itself, ~30 ms in this case. What happens where the electrons (etc) are moving relativistically?
Chronos said:
The thought experiment is flawed. It assumes material properties that cannot and do not exist. A neutron star is the densest known state of matter in the universe, and it does not exhibit any such properties.
Bjørn Bæverfjord said:
Some pulsars (neutron stars) rotate with a period that would give a surface velocity of something like 0.7c if it was a rigid body. It is clearly possible to imagine something to rotate fast enough as to experience measurable relativistic effects.
It's not hard to do the calculation; some neutron stars will have a surface that is moving relativistically (say, >0.1c).

However, what I was referring to is electrons trapped in intense magnetic fields, above the neutron star's surface - they will co-rotate with the star. Here is a simple account of neutron stars (electrons trapped in the magnetic field is mentioned near the bottom).
 
  • #21
If all that were true I could use a plate spinning on top of a stick and claim interdivisional displacement.

The different parts of the plate would experience time at different rates. Slower closer to the edge. It wouldn't be interdivisional travel though. If what I said is true. It would mean that although the plate and everything in the universe is part of the same constant time flow. The outer edges experienced less of the flow, and aged slower, but it is all part of the same constant time dimension. The outer edges just didnt experience the full affects of the constant time.

If there were no constant time. Wouldn't that mean that almost everything would be in its own time dimension, cause things move at different rates?

Or if there was a clock created at the beginning of the universe and that clock always remained perfectly stationary. It would show the exact constant time. If everything else created at the beginning was also given clocks, and those things did move. Then you were to later compare times. The moving objects clocks would show less time compared to the stationary clock. It wouldn't mean that the moving objects are in their own space time (or arent truly as old). It would just mean their clocks are slow. The moving objects though would have only aged and experienced as much time as their clocks showed. So could you say time is constant, the experience of it is relative?
 
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  • #22
Here's something that I just can't get my head round. Maybe somebody can paint a clear picture for me.

Rotating disc where the outer edge is traveling close to C.

Lorentz transformations ?
 
  • #23
Wouldn't that mean that almost everything would be in its own time dimension, cause things move at different rates?
Yes; which is why building a clock no more than an OOM or two more accurate than the best we have today would likely not be worth the effort - comparing any two such clocks would tell you ... what, exactly?

Note that the clock synchronisation problem already occurs with our GPS system - due to full GR effects, not just SR ones - and what's used to handle this is just one of several possible ways to do it (see the S&GR section for threads which discuss this).
 
  • #24
I think Nereid's post correctly explains the matter and I have nothing to add.

I would like to comment on the 3 or 4 posts above that say or suggest going back in time as you cross the disc. That is not possible nor did Albert Einstein come close to actually saying it. In fact his Relativity position explains why it is relative to a secondary point but impossible for the secondary point to move to the primary point and maintain the Relative Characteristics of the secondary point.
 
  • #25
I would like to comment on the 3 or 4 posts above that say or suggest going back in time as you cross the disc.

I wasn't saying that you would go back in time by crossing the disc. All I am theorizing is that there is a constant time. Time is constant. It is just that different objects experience it at different rates. The faster something moves the farther off its time becomes to true constant time. If I were to fly around the world at just under C. For 100 years going by a stationary clock. Even though the watch I was wearing would only show maybe 5 mins has passed, and I would only feel, and aged 5 mins. Doesnt mean that I am not really still 100 years older. Constant time still passed by for 100 years. I just didnt experience all the affects of it. Just like the clock at the outer edge of the disc. The disc always turned 29 RPMs and made 1,524,240,000 rotations, 100 years worth of rotations at that speed. The outer clock will say only 5 mins has passed. Even though it still made 1,524,240,000 rotations at 29 RPMs. It can't do that in 5 mins. So that means the clock is wrong.
 
  • #26
If I may say so UglyEd, your question (and confusion) is a very common one, for folk when they first encounter Relativity - it's all so ***ly counterintuitive!

However, if you take the trouble to work through this - especially if you check for yourself what the predictions are and what the results of the honest-to-goodness experiments are - then I think you'll find that it is at least fully consistent.

In particular, you'll no doubt get an appreciation of why 'true constant time' doesn't exist (indeed, within GR, it *cannot* exist).
 
  • #27
UglyEd I did not mean to suggest you said you would go back in time. Those who posted below you did.
 
  • #28
I very well could be not catching on to something. Given the facts that I know are true. This is the conclusion that seems to work.

It is true that a clock that is moving will show a slower passage of time compared to a stationary clock. Like the experiment that was done with the 2 clocks one on a plane one on the ground. Right?

Also I saw a show about space, time and relativity. There were twin brothers. That worked for NASA. One had orbited the Earth a few times. He was saying how he is now slightly younger (very small amount) than his brother. Do to the speed he traveled at.

I see that as being partly true. Although he has aged less, and felt the affects of less time. He is still just as old, he has still been in existence the same amount of time. Like the clocks in the river. If the brothers were the clocks (that measured time by the amount of water/time that passed them by). One clock stayed in place, the other floated down stream a little. The one that floated would have had less water pass by it. It would therefore show less time, than the stationary one. The river has always flowed at the same rate though (time kept moving). The stationary clock would have even kept track of the exact amount of flow. So even though one of the clocks would show, feel, and have experienced less of the rivers flow. Both of the clocks have been in the river the same amount of time. The brothers would also be just as old, or in existence the same amount of time.

If the clocks and plane scenario is true. Then it should be true that the outer fast moving clock on the outer edge of disc would show less time has passed compared to a slower moving one in the center. The outer clock would have even aged, felt the affects of, and experienced less time.

In that situation though the disc really did rotate 1,524,240,000 times. At a rate of 29 RPMs. The outer clock, even if it doesn't feel the affects. Did make the 1,524,240,000 rotations at 29 RPMs. That can't happen in the 5 mins that the outer clock shows. So couldn't that only mean that it didnt keep accurate track of time? It took track of the all time that passed it (like in the river scenario) but it didnt keep track of all the time that had really flowed. Just because it only had 5 mins worth of time, doesn't mean that 100yrs didnt flow.

If that is all true then wouldn't it mean. That time is constant, just objects experience, or have it pass them at different rates. If that wouldn't all be the correct reasoning. Then what would be?
 
  • #29
AWolf said:
Rotating disc where the outer edge is traveling close to C.

Lorentz transformations ?

As nobody else has noticed the significance, I'll try to answer my own question.

The further you travel from centre of the spinning disc, the faster you are travelling. According to Lorentz contraction, the faster you go, the more your length contracts. Length in the case being the circumference at a radius from the centre.
If you map circumference/velocity/contraction you will find that at the speed of light, the outer edge of the disc has a circumference of zero.

As you spin the disc up, the faster you go, the more the outer edge curves back on itself.
 
  • #30
AWolf I think something in that post is not exactly correct.

UglyEd:
If you were to read five explanations of Einstein's Relativity Theories you would get five different explanations some would have slight differences and some would be completely wrong. I believe I have a good understanding of his Theories but I would never be so bold as to attempt to explain them. Complex multi-level thoughts are difficult to explain. Why I have never read his theories explained correctly I guess. Actually I have read one book that explained them correctly.

I just finished an Internet search and went to four different sites to see if it was explained correctly. Three were mostly wrong and one site had you leaving Earth in a spaceship and returning to Earth 2000 years in the past. Einstein never said you could go faster than the speed of light and return to your starting point before you left.

I suggest you use the source that I learned the theories from. I can absolutely guaranty his explanations are 100% correct. The book I used was written by Albert Einstein. I had to read it very slowly making notes and reading some parts three or four times to fully understand what I thought he meant. I am positive I did not understand 100% of the material closer to 90%.

Read

Relativity
The Special and General Theory
By: Albert Einstein
 
  • #31
AWolf I know what bothered me:

When using Lorentz Contraction the velocity of the observer has to be a fraction of the speed of light it cannot be the speed of light so you could not have v squared / c squared = 1 so you can never end up with 0.

While the square root of zero is zero you can not use it to get a real solution from the equation or any equation.
 
  • #32
Alex Massi said:
AWolf I know what bothered me:

When using Lorentz Contraction the velocity of the observer has to be a fraction of the speed of light it cannot be the speed of light so you could not have v squared / c squared = 1 so you can never end up with 0.

While the square root of zero is zero you can not use it to get a real solution from the equation or any equation.
Granted, you cannot have a velocity of C, but even with a velocity just less than C, the contraction will result in the outer edge curving back in towards the centre.
 
  • #33
I had never heard of the Lorentz Contraction. I checked a site about it. Isn't it more of an observed contraction, than an object actually contracting? The site mentioned a spaceship flying past an observation post at near C. From the ship the observation post would look contracted. From the observation post the ship would look contracted. It didnt say that the ship or observation post would actually be contracted. It also said that the Lorentz Contraction only happens in the same direction as travel. The observation post would look thinner but still the same height.

Even if the Lorentz Contraction does physically contract an object, it doesn't really matter for this. It doesn't matter how fast the disc spins. Even if it is spinning slow enough for the contraction to be minuet. The outer clock will still be moving faster and still show less time than a clock at the center. So the clock would still be wrong when it came to the RPMs and the number of rotations that happened. It would be off by less than if it were spinning near C but still off and would still show the same conclusion.
 
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  • #34
The theory was used by Loentz to explain the contraction of a object in relation to its motion. Einstein used the basics of the equation for some of his mathematics. Einstein proved that the contraction was not the object changing but a change in space and time.

Tell me how exactly are you going to get to the second clock to see the time and if you go to it will the two clocks be the same time?
 
  • #35
Awolf you are correct the theory works if the speed is 1 mile an hour. Very hard to measure the contraction but it changes. The change would be about the thickness of an atom - my random guess.
 

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