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the speed of light question

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    #62
    AllForIt
    Registered Users Posts: 8,269 ✭✭✭AllForIt


    skallywag wrote: »
    Closer to home Time Dilation needs to be factored into GPS systems to make them work correctly. Meaning the run of the mill GPS system in your car etc would not work correctly without adjusting for Time Dilation.

    Here is an interesting read (albeit fiction) on Tachyons by the way ...

    https://en.wikipedia.org/wiki/Timescape

    And this has been proven. An atomic clock (meaning it measures time to fractions of a second) was put on a orbiting satellite and after a period of time it was brought back to earth. The time did not match the time on it's paired atomic clock on earth, it was out by an 'atomic' fraction thus time did not move at the same speed for both clocks. If they did the readings would be exactly the same but they weren't.


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    #63
    skallywag
    Registered Users Posts: 2,987 ✭✭✭skallywag


    AllForIt wrote: »
    And this has been proven. An atomic clock (meaning it measures time to fractions of a second) was put on a orbiting satellite and after a period of time it was brought back to earth. The time did not match the time on it's paired atomic clock on earth, it was out by an 'atomic' fraction thus time did not move at the same speed for both clocks. If they did the readings would be exactly the same but they weren't.

    Indeed, and it is exactly this difference that needs to be compensated for in the calculations used in GPS.


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    #64
    blinding
    Banned (with Prison Access) Posts: 7,466 ✭✭✭blinding


    Perhaps its all just an Idea ~ ~ Is there anything more Powerful than an Idea ? ?


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    #65
    Gregor Samsa
    Registered Users Posts: 8,908 ✭✭✭Gregor Samsa


    Tiger20 wrote: »
    what and how would the speed of light mean/influence to a blind person? If the SOL is an observed phenomenon, then is it relevant to unobservation? Is the SOL therefore not a human construct, because to an atom it is irrelevant. At what about the thing called spooky something or other.

    Being blind doesn’t mean the laws of physics don’t apply to you. An “observer” isn’t someone who can see, it’s any entity that takes a measurement. Anyway, light affects blind people - they can get sunburned from the sun’s photons just like a sighted person.

    The “spooky action from a distance” was, as EmmetSpiceland said, Einstein’s dismissal of Quantum Entanglement. QE has since been shown through experimentation to actually exist. However, despite the fact that the changes in the two particles can be observed instantaneously, it doesn’t break the law of causality, and faster than light communication is not occurring.

    Say you have one entangled particle on Mars, and one on earth. You hope to be able to set the state of the one on Mars to a particular value (say1), and then the people on earth will be able to measure their particle, and instantly see that the value is 1. That way you can sent a message faster than light.

    However, it doesn’t work that way. When the person on earth measures their particle, the result is actually totally random - it’s not whatever was set on Mars. So you’re not receiving any information from your colleague on Mars at all. So when the person on Mars changed the state of theirs, the one on earth changes too. But when the person in earth “reads” theirs, not only does the state randomly change, the one on Mars instantly does too, basically erasing the information that they intended to send. While the states of the two particles do change instantly, no information is passed between the two, and causality is not violated.

    Edit: Aristotle explained it better above.


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    #66
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    Gregor Samsa wrote: »
    Edit: Aristotle explained it better above.

    Disagree, I think your example makes it more clear. :)


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    #67
    Gregor Samsa
    Registered Users Posts: 8,908 ✭✭✭Gregor Samsa


    Tiger20 wrote: »
    And another question I have previously wondered is this. Say you are flying on a plane to a destination, ETA 2 hours from now. The place you are flying to currently exists, but does not yet exist relevant to you on the plane. It will only come into existence for you once you arrive. As such your destination is notional to you. So where does the time that you arrive at come from? Is it created as you fly there? Or does the time already exist in reality, just like your destination does, but you haven't experienced it yet. Therefore is all time not already in existence!

    There’s nothing in physics that says your destination doesn’t exist.

    The Copenhagen Interpretation says that the state of a wave function doesn’t come into existence until it is observed, but that’s not the same as saying the entity doesn’t exist. It was this position that the famous Schrödinger's Cat thought experiment is about.

    The Copenhagen Interpretation is only one theoretical model, and probably not the most likely one.

    The thing is, though, even if it was true - there are people in the city you’re flying to, so there are observers there. So the wave function will have already collapsed. But let’s assume the city is totally unpopulated by any life. It then becomes the old puzzle of “if a tree falls on the woods, the there’s no one there to see it, does it make a sound?”

    The answer is, if you go into the woods and observe a tree that has fallen, then you have collapsed the wave function for that tree to its “fallen” state (I’m massively simplifying). One that happens, causality has to be maintained, so the wave functions of all the events that caused the tree to fall must be collapsed too - and this would include the air pressure changes the tree falling creates, and subsequently the sound.

    So it’s not that your uninhabited destination wouldn’t exist until you get there. It’s that it would be held in a state of superposition until you get there, then once you do, the state collapses into the one you observe, and anything yo do to investigate the state you find it in only leads you to events that created that state - you will find an unbroken trail of causality.


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    #68
    blinding
    Banned (with Prison Access) Posts: 7,466 ✭✭✭blinding


    Does Quantum Entanglement suggest that there is no such thing as Free Will i.e. That everything has already been decided !
    !

    To be simplistic about it !


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    #69
    Gregor Samsa
    Registered Users Posts: 8,908 ✭✭✭Gregor Samsa


    blinding wrote: »
    Does Quantum Entanglement suggest that there is no such thing as Free Will i.e. That everything has already been decided !
    !

    To be simplistic about it !

    Quantum mechanics does *possibly* suggest there’s no such thing as free will - not because the results are already decided, but because the results of quantum observations are inherently random. However, the phenomenon of probability puts some limits on that. Once a system is in place, overall the system acts in a predictable way, even if there’s uncertainty at the quantum level. You start getting into the cutting edge of what all this means for the “real world” at that point, and there aren’t definitive answers.

    From a quantum point of view, there may be no free will (as there’s no intelligence guiding quantum events), but in the macro sense in our day to day lives, that may not really matter much, and we still “experience” free will.


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    #70
    Tiger20
    Registered Users Posts: 87 ✭✭Tiger20


    Gregor Samsa wrote: »
    There’s nothing in physics that says your destination doesn’t exist.

    The Copenhagen Interpretation says that the state of a wave function doesn’t come into existence until it is observed, but that’s not the same as saying the entity doesn’t exist. It was this position that the famous Schrödinger's Cat thought experiment is about.

    The Copenhagen Interpretation is only one theoretical model, and probably not the most likely one.

    The thing is, though, even if it was true - there are people in the city you’re flying to, so there are observers there. So the wave function will have already collapsed. But let’s assume the city is totally unpopulated by any life. It then becomes the old puzzle of “if a tree falls on the woods, the there’s no one there to see it, does it make a sound?”

    The answer is, if you go into the woods and observe a tree that has fallen, then you have collapsed the wave function for that tree to its “fallen” state (I’m massively simplifying). One that happens, causality has to be maintained, so the wave functions of all the events that caused the tree to fall must be collapsed too - and this would include the air pressure changes the tree falling creates, and subsequently the sound.

    So it’s not that your uninhabited destination wouldn’t exist until you get there. It’s that it would be held in a state of superposition until you get there, then once you do, the state collapses into the one you observe, and anything yo do to investigate the state you find it in only leads you to events that created that state - you will find an unbroken trail of causality.

    As I said, I am still trying to get my head around this stuff, it is kinda head wrecking, but fascinating. I suppose if it took Einstein a lifetime it will take more than a few posts on boards to understand.

    I agree about your destination existing, and that wasn't really the question I am trying to pose/answer. It's the time part of it that I still dont get. If you are walking somewhere on a footpath, then the path to your destination already exists. But the time taken to get there doesnt yet exist, but it can be measured and correctly stated at what time you will get there, so where has this time come from?

    Sorry if what I am asking is physics for dummies 1, still trying to catch up!


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    #71
    blinding
    Banned (with Prison Access) Posts: 7,466 ✭✭✭blinding


    Tiger20 wrote: »
    As I said, I am still trying to get my head around this stuff, it is kinda head wrecking, but fascinating. I suppose if it took Einstein a lifetime it will take more than a few posts on boards to understand.

    I agree about your destination existing, and that wasn't really the question I am trying to pose/answer. It's the time part of it that I still dont get. If you are walking somewhere on a footpath, then the path to your destination already exists. But the time taken to get there doesnt yet exist, but it can be measured and correctly stated at what time you will get there, so where has this time come from?

    Sorry if what I am asking is physics for dummies 1, still trying to catch up!
    Can anyone actually prove that Time Exists ?


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    #72
    Gregor Samsa
    Registered Users Posts: 8,908 ✭✭✭Gregor Samsa


    blinding wrote: »
    Can anyone actually prove that Time Exists ?

    Funnily enough, physics has an operational definition of time as “what a clock reads” - which makes it sound very unscientific.

    Time itself can be different for different observers, so it’s measurement is nothing universal. However the concept is, and there’s a robust theoretical and observational/experimental framework that outlines that the arrow of time can only travel in one direction (past to future). It’s wrapped up in the concepts of entropy and a phenomenon known as the “light cone” which is the sum of all theoretical paths of a photon from a point into the future or the past. Furthermore, time can’t be separated from space, so much so that it’s referred to as a single unit - space time. Time is a dimension of space time, just as length, breath or height is.


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    #73
    blinding
    Banned (with Prison Access) Posts: 7,466 ✭✭✭blinding


    Gregor Samsa wrote: »
    Quantum mechanics does *possibly* suggest there’s no such thing as free will - not because the results are already decided, but because the results of quantum observations are inherently random. However, the phenomenon of probability puts some limits on that. Once a system is in place, overall the system acts in a predictable way, even if there’s uncertainty at the quantum level. You start getting into the cutting edge of what all this means for the “real world” at that point, and there aren’t definitive answers.

    From a quantum point of view, there may be no free will (as there’s no intelligence guiding quantum events), but in the macro sense in our day to day lives, that may not really matter much, and we still “experience” free will.
    Can it be proved that the quantum observations are actually random ?

    They could look random and have been already decided. They could have been random at one time but not random at another time again depending if Time Exists !


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    #74
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    blinding wrote: »
    Can it be proved that the quantum observations are actually random ?

    Depends on which interpretation of quantum mechanics you look at as already mentioned by Gregor Samsa. I'd recommend reading up on Bell's theorem and the associated experiments. :)


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    #75
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,698 Mod ✭✭✭✭Capt'n Midnight


    Deleted User wrote: »
    They said the speed of sound could not be broken.
    And yet it had been broken by bullets and shells hundreds of years earlier. Strange that.

    The Sound Barrier was named because it was difficult to get through. Flying conditions are a tad different when you go supersonic. That's why most modern airliners have a top speed of around 0.95 Mach.

    The next 'barrier' is the Thermal Thicket when you go beyond Mach 2.2 That's where aluminium alloys weaken when friction with the air takes them over 200 degrees. One of the reasons the Tu-144 could go faster that Concorde was because it was flying in colder air over Russia.


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    #76
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,698 Mod ✭✭✭✭Capt'n Midnight


    air wrote: »
    It is in this respect, relativity is 100% accurate at present & is used in things like GPS, it wouldn't work if not adjusted for it's effects.
    The correction for us being stuck further down a gravity well is about seven times larger.

    GPS satellites transmit at 10.22999999543 MHz so you can receive them 10.23MHz


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    #77
    railer201
    Registered Users Posts: 968 ✭✭✭railer201


    y0ssar1an22 wrote: »
    a question that has puzzled me for a while...

    1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

    2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

    if the rules of physics hold for scenario 1, why not scarios 2?

    is there a simple explanation here?

    i dunno, maybe we just don't have an answer?

    There's a simple explanation that's not simple to understand, for me at any rate. The speed of light is relative to the observer. Each driver would see the other car approaching at the speed of light. A person at the side of the road would see each car approaching also at the speed of light. Time slows down for the drivers on board the cars is how it works. Head bendy stuff. It has been proven by various experiments, such as taking an atomic clock on a jet flight and comparing the times with another atomic clock on the ground.


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    #78
    standardg60
    Registered Users Posts: 4,242 ✭✭✭standardg60


    My own long thought out theory.
    By being measurable at all our speed of light bugs me, it essentially creates a time delay in what we perceive as what's happening now. If you think about it everything that we experience 'now' has already happened. When did it happen? It happened the speed of light ago, the only difference being your own proximity to it.
    Why did history happen to unfold the way it did? Did we control it or had it already happened and we just 'experienced' it.
    What if the future has already happened and we are just wending inevitably towards it?
    I think that everything in the universe has already happened, but they occurred at infinitely different speeds of light and we are simply passing through those different time delays. If we are not then why is last week different to this week and different to next week?
    The only plausible explanation that i'm comfortable with is that last weeks speed of light is different to this weeks and will be different again next week.

    I know it's a bit crazy but it answers my questions.


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    #79
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    standardg60 wrote: »
    The only plausible explanation that i'm comfortable with is that last weeks speed of light is different to this weeks and will be different again next week.

    We know by analysing the data from the Oklo natural reactor that the speed of light has not changed in 1.7 billions years, so it certainly did not change last week.
    https://www.forbes.com/sites/startswithabang/2018/10/04/earths-first-nuclear-reactor-is-1-7-billion-years-old-and-was-made-naturally/


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    #80
    skallywag
    Registered Users Posts: 2,987 ✭✭✭skallywag


    Capt'n Midnight wrote: »
    The correction for us being stuck further down a gravity well is about seven times larger.

    GPS satellites transmit at 10.22999999543 MHz so you can receive them 10.23MHz

    The Radio transmission from the satellites themselves is in the GHz region, and is a multiple of the 10.23 Mhz.

    The 10.23 Mhz is the 'base frequency' on-board the satellite itself, which gets multiplied up to the GHz band before actual transmission from the satellite's antenna, and then subsequently down-converted again at the Receiver side.

    It is indeed the variation in the 10.23 Mhz base frequency between satellite and earth station which needs correction though.


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    #81
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,698 Mod ✭✭✭✭Capt'n Midnight


    standardg60 wrote: »
    My own long thought out theory.
    By being measurable at all our speed of light bugs me, it essentially creates a time delay in what we perceive as what's happening now. If you think about it everything that we experience 'now' has already happened. When did it happen? It happened the speed of light ago, the only difference being your own proximity to it.
    Until the discovery of the telegraph speed of light delays weren't noticeable outside of astronomy.

    every-single-action-of-god-including-every-prophet-chosen-in-30667035.png

    1,500Km = 5 milliseconds of light travel. If you dropped an object it would fall a tenth of a millimetre in that time.



    Also our consciousness measures time fluidly like the whole deja vu thing.


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    #82
    standardg60
    Registered Users Posts: 4,242 ✭✭✭standardg60


    Deleted User wrote: »
    We know by analysing the data from the Oklo natural reactor that the speed of light has not changed in 1.7 billions years, so it certainly did not change last week.
    https://www.forbes.com/sites/startswithabang/2018/10/04/earths-first-nuclear-reactor-is-1-7-billion-years-old-and-was-made-naturally/

    What i like to ask myself is what is causing our sense of the passage of time. What makes the past the past and the future the future.
    If the speed of light is a constant and always has been throughout the universe, then why does anything change.
    We see change because we can see things which happen at a different relative speed to us.
    Could this not be the case on a universal scale? That different areas of the entire universe are all moving at different speeds of light, therefore causing a difference in time.
    Someone posted early in the thread a link that posited that indeed there may be light speeds at the edge of the universe that could be many times c but that we don't need to question that as it's not relevant to us.
    But what if it is that question that is the meaning of life?
    That that is the reason why our time passes.
    It's all relative!


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    #83
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    standardg60 wrote: »
    What i like to ask myself is what is causing our sense of the passage of time. What makes the past the past and the future the future.
    If the speed of light is a constant and always has been throughout the universe, then why does anything change.
    We see change because we can see things which happen at a different relative speed to us.
    Could this not be the case on a universal scale? That different areas of the entire universe are all moving at different speeds of light, therefore causing a difference in time.
    Someone posted early in the thread a link that posited that indeed there may be light speeds at the edge of the universe that could be many times c but that we don't need to question that as it's not relevant to us.
    But what if it is that question that is the meaning of life?
    That that is the reason why our time passes.
    It's all relative!

    I don't see why you think it is necessary for the the speed of light to vary in order for things to change. As long as light has a speed, constant or otherwise, then information can be transferred and therefore things in turn change.


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    #84
    fillup
    Registered Users Posts: 560 ✭✭✭fillup


    Slightly off topic but seems like I might get an answer here from one of the Boardsie Boffins...

    Out of curiosity I was googling how Michelson measured the speed of light back in 1927
    As explained in this video, they shone a beam of light between two mountains and timed how long it took for the light to complete a round trip between the 2 points.
    At around the 5min 30 sec mark the lecturer explains how they measured the distance between the two mountain tops to within 8 cms despite them being over 35km apart
    They used triangulation and a 50m measure to to calculate the distance but I still can't figure out how they calculated the distance over the rough terrain between the 2 peaks

    Anybody care to explain?
    Tnks

    Link to video -
    https://youtu.be/I_RG7R15eCM


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    #85
    blinding
    Banned (with Prison Access) Posts: 7,466 ✭✭✭blinding


    fillup wrote: »
    Slightly off topic but seems like I might get an answer here from one of the Boardsie Boffins...

    Out of curiosity I was googling how Michelson measured the speed of light back in 1927
    As explained in this video, they shone a beam of light between two mountains and timed how long it took for the light to complete a round trip between the 2 points.
    At around the 5min 30 sec mark the lecturer explains how they measured the distance between the two mountain tops to within 8 cms despite them being over 35km apart
    They used triangulation and a 50m measure to to calculate the distance but I still can't figure out how they calculated the distance over the rough terrain between the 2 peaks

    Anybody care to explain?
    Tnks

    Link to video -
    https://youtu.be/I_RG7R15eCM
    Why would they measure over the rough terrain ? Light goes directly except in exceptional circumstances !


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    #86
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    fillup wrote: »
    Slightly off topic but seems like I might get an answer here from one of the Boardsie Boffins...

    Out of curiosity I was googling how Michelson measured the speed of light back in 1927
    As explained in this video, they shone a beam of light between two mountains and timed how long it took for the light to complete a round trip between the 2 points.
    At around the 5min 30 sec mark the lecturer explains how they measured the distance between the two mountain tops to within 8 cms despite them being over 35km apart
    They used triangulation and a 50m measure to to calculate the distance but I still can't figure out how they calculated the distance over the rough terrain between the 2 peaks

    Anybody care to explain?
    Tnks

    Link to video -
    https://youtu.be/I_RG7R15eCM

    This is the paper about their measuring technique. If you still don't understand something about the method after reading it let me know. :)


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    #87
    fillup
    Registered Users Posts: 560 ✭✭✭fillup


    blinding wrote: »
    Why would they measure over the rough terrain ? Light goes directly except in exceptional circumstances !

    They had to cover rough terrain to measure the distance between their measuring apparatus- they couldn't run a 35km measuring tape between the two sites.


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    #88
    fillup
    Registered Users Posts: 560 ✭✭✭fillup


    [Deleted User] wrote: »
    This is the paper about their measuring technique. If you still don't understand something about the method after reading it let me know. :)

    Cheers - i'll check it out and report back!


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    #89
    Alf Veedersane
    Registered Users Posts: 24,552 ✭✭✭✭Alf Veedersane


    y0ssar1an22 wrote: »
    a question that has puzzled me for a while...

    1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

    2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

    if the rules of physics hold for scenario 1, why not scarios 2?

    is there a simple explanation here?

    i dunno, maybe we just don't have an answer?

    You should also have asked if Schrödinger's cat is in car A or car B.


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    #90
    standardg60
    Registered Users Posts: 4,242 ✭✭✭standardg60


    Deleted User wrote: »
    I don't see why you think it is necessary for the the speed of light to vary in order for things to change. As long as light has a speed, constant or otherwise, then information can be transferred and therefore things in turn change.

    It has to be necessary. If we can see that the universe is expanding, then it must be expanding at a different speed to ours. If we were expanding at the same speed then we wouldn't see it.


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    #91
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    standardg60 wrote: »
    It has to be necessary. If we can see that the universe is expanding, then it must be expanding at a different speed to ours. If we were expanding at the same speed then we wouldn't see it.

    I think you are getting a bit confused between the speed of light and the speed of the expansion of the universe. They are not the same thing, but that does not suggest that the speed of light is not constant. The speed of the expansion of the universe is instead determined by the Hubble constant (~68km/s per megaparsec).

    As for your last sentence, the outer parts of the universe (beyond the Hubble radius) are actually receding at a speed greater than the speed of light. Therefore, any light emitted outside of this radius can never and will never be detected by us.


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