Does time go slower underwater? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: July 12, 2020, 08:57:54 am
content: Light travels fastest in a vacuum. When it passes through water it goes slower and causes refraction. Seeing it goes slower in water, would not time also pass more slowly in water to an observer outside the water?

author: tom66
author_rank: Super Contributor
timestamp: July 12, 2020, 09:00:04 am
content: Elementary physics understanding here but yes. Water has a lot of mass, much more than air, and mass/gravity influences the passage of time. So time will be a little slower underwater. I am not sure by how much.

author: greenpossum
author_rank: Frequent Contributor
timestamp: July 12, 2020, 09:06:26 am
content: I know I saw my whole life flash past my eyes when I almost drowned, so I think yes.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 12, 2020, 09:17:59 am
content: Quote from: tom66 on July 12, 2020, 09:00:04 amThere is a tiny effect of gravity on how "fast" the time passes. This is a tiny effect from general relativity, but it is some tiny it need things like an atomic clock (maybe a rubidium oscillator could work) to observe it. It is the gravitational field, not the mass density close by.For a human one may get the feeling that time slows down, as underwater is usually and unusual place to be, so one is often more excited and this can change the perception of time.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2020, 10:16:56 am
content: Heh, not like that. You'd have to make space itself have an index of refraction -- which, along with some other crazy things, is effectively what supermassive objects do, but due to the other crazy things, you can't exactly live near them.That there are two speeds of light in a medium, like water, means you can get shockwave effects like Cerenkov radiation, when a charged particle goes faster than that speed. This isn't possible in vacuum, where the maximum propagation velocity is equal for both matter and light.Tim

author: eti
author_rank: Super Contributor
timestamp: July 12, 2020, 02:33:10 pm
content: Quote from: Circlotron on July 12, 2020, 08:57:54 amFill your house to the brim wiith water, and then try to get the housework done; I promise you time will go slower...

author: Rick Law
author_rank: Super Contributor
timestamp: July 13, 2020, 12:06:38 am
content: Quote from: Kleinstein on July 12, 2020, 09:17:59 amThere will not be a "slow down of time" that the human (or atomic clocks) can feel, even if it is as strong as can be, one would not experience time any different than normal progression.It is easier to look at the situation of gravity-based time dilation for the aspect of how observers feel the passing of time.Time passage under strong gravity runs slower. So, ifobserver 1 is closeto a black hole andobserver 2 is farfrom the black hole, observer 2 will see observer 1's clock running slower. But,both observer 1 and observer 2 will feel their time progressing at the normal rate. So, observer 1's time doesn't go slower - every one traveling with observer 1 will time is progressing normally. Observer 1 however can see observer 2's clock running fast. Observer 2 feel his time passing normally and see observer 1's time being slower than his.Eventually, as observer 1 reach near the event horizon of the black hole,Observer 2 will see observer 1's clock running slower, and slower, and slower, and slower. Every micro second for observer 2, observer 1's clock is slower than the micro-second before as observer 2's sees it. So slow it almost seem to observer 2 like time stopped for observer 1.As to the question: "If one wait long enough, will observer 2 ever see observer 1's clock come to a stand-still?" That is an open and complicated question. What Physicist all seem to agree is that they are stuck on the surface at the 3D "neck" of the event horizon - for the rest of the life expectancy of the black hole, they just seem to stuck there, may be they are still falling in (clock still moving), but they never seem to get there (clock stopped).Observer 1 on the other hand, would feel no change time-wise. Observer 1 (and traveling companions) will feel one second as one second, and will be so until eventually they all got killed by whatever kill them first, be it radiation or being spaghettified.So, the guy in the water will not experience a slow clock.They feel time running normal but they see us on dry land are ones with a clock running fast. The guy in the vacuum of space would see our clocks being slow, and the wrist-watch the fish is wearing is running even slower still.That said, now the formal definition of time isthe unperturbed ground-state hyperfine transition frequency of the caesium 133 atom. I am not sure you can do that measurement with the whole apparatus under water. So it will have to be some kind of transferred standard set up first, then use that standard to measure time under water -- which would be an interesting Experimental Physics exercise.Now, time for a joke:Mary and Sue were traveling around the universe, and they came across a black hole. It looks so wondrous, they decided to go in for a look, andEDIT: wording to make it easier to read. This is a complicated matter and I'm trying to make the wording clearer.

author: Circlotron
author_rank: Super Contributor
timestamp: July 13, 2020, 12:35:21 am
content: Quote from: Rick Law on July 13, 2020, 12:06:38 amI wasn't talking about looking at your own local clock. I was saying if you were on dry land and you looked at the underwater clock. So you are saying the underwater clock =would= *appear* to be running slow to the observer on dry land?

author: Rick Law
author_rank: Super Contributor
timestamp: July 13, 2020, 01:12:44 am
content: Quote from: Circlotron on July 13, 2020, 12:35:21 amI was framing my reply more towardsKleinstein's reply saying "For a human one may get the feeling that time slows down, as underwater is usually and unusual place to be, so one is often more excited and this can change the perception of time." So I frame the reply to contrast perception fromobserver to selfverses perceptionbetween different observers. One's perception in time is a case of observer independence. Doesn't matter what frame you are in, your time progression (thus perception) is exactly the same.The time dilation only comes in when compared between frames of reference.But now directly to your point:"So you are saying the underwater clock =would= *appear* to be running slow to the observer on dry land?"Yes it will, observe on dry land (reference frame 1) will see an underwater clock (in reference frame 2) as slower due to slower speed of light under water.The time one experience is a combination of time and space one passes. Each of us occupies a different space and each of us are doing different things (standing up is an acceleration away from gravity, turning to get into the bathroom is an experience of centrifugal acceleration, going upstairs is a decrease in gravitational acceleration...). Given each of us a clock of adequate precision, it will all read different time has passed by the end of the day.

author: StillTrying
author_rank: Super Contributor
timestamp: July 13, 2020, 01:19:46 am
content: What effect would 2 or more strongbut opposite and cancellinggravitational fields have on the speed of a clock.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 13, 2020, 01:44:46 am
content: AFAIK, even black or white holes, composed of exotic matter, still exhibit time dilation, so there is no such thing as cancelling gravity.Tim

author: Rick Law
author_rank: Super Contributor
timestamp: July 13, 2020, 02:07:19 am
content: Quote from: StillTrying on July 13, 2020, 01:19:46 amQuote from: T3sl4co1l on July 13, 2020, 01:44:46 amHe probably doesn't mean eliminating gravity, but merely staying on a Lagrange Point where the force of gravity is equal but in opposite direction.But no luck -- At that point (and that is a moving point), gravitation fields cancels out - which means the space warping cancels out and space is flat. Time dilation due to space warping is zero since at that point space is flat. However, time dilation due to acceleration is not zero - read on...Since two objects (say Earth and Moon) cannot be stationary to each other or they will collapse into each other due to mutual attraction. So, the two objects has to move to fight the mutual attraction. Both objects because Moon and Earth each orbit around the center of gravity of Earth+Moon, so both objects are moving and that point is a moving point.Since you are trying to stay on a point (for t>0) that is a moving point, you must accelerate to move with it. So you will get time dilation due to your acceleration.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 13, 2020, 02:21:57 am
content: You're also in a gravity well, so time will be slowed (relative to infinity) for that reason. Unless it works out that the Lagrange point is truly neutral (zero potential energy relative to infinity, which is also to say it's not a stable orbit), I'm not very familiar with orbital mechanics. But anyway, they will be a rotating system, which I think screws that all up anyway; your orbit is with respect to the bodies, which are themselves accelerating (towards each other), which is not an inertial frame of reference.

author: StillTrying
author_rank: Super Contributor
timestamp: July 13, 2020, 02:31:39 am
content: "Point where the force of gravity is equal but in opposite direction."Yes 2 heavy equal planets rotating around each other, the middle no-gravity point could be stationary.

author: EEVblog
author_rank: Unknown
timestamp: July 13, 2020, 03:29:00 am
content: Technically the light itself does not slow down in water, it's the combined electromagnetic wave effect caused by the material:

author: hamster_nz
author_rank: Super Contributor
timestamp: July 13, 2020, 05:41:26 am
content: Quote from: Circlotron on July 12, 2020, 08:57:54 amWater has as refractive index of 1.333. So if my math is right that makes the speed of light about 75% of that in a vacuum (which is pretty much the same as air).Even with a few tonnes of of water (cubic meters) it won't make an appreciable difference to time - according to Wikipedia...QuoteSo just roughly banging numbers about. A few tonnes of water might make 0.000 000 000 000 000 000 001 of a second's difference, over a year.

author: Rick Law
author_rank: Super Contributor
timestamp: July 13, 2020, 05:43:55 am
content: Quote from: EEVblog on July 13, 2020, 03:29:00 amI've seen that guy(in the video) in other presentations, he is rather good.Whether how light slow down or not is an interesting point to bring up, but how it slow down really doesn't alter the fact that it did slow down. That however brings up a couple of cans of worms that is very interesting. I was debating whether I should bring those complication up - or not, but with that video, that gives me a reason to get into it. (I actually had passion about the first can of worm once upon a time -- way before SI's definition of Time quantity became real)First can of wormsAt the time Eisenstein came up with time dilation and speed of light being a important factor, Time was not we defined as Time today in the SI unit -- that is why I included the SI definition of time in my first reply.In Eisenstein's days, EM wave (light) propagation was understood to be electric field inducing a magnetic field which in-turn induce an electric field which in-turn induce a magnetic field, so on, so the EM wave propagates. Fine, we accept that. So, how fast one field induce the next how that next field induce another next, so on, takes time, so there is a speed limit, fine, we accept that. And with that light/EM wave and time is rather closely linked as other theories developed, and in particular, how Eisenstein think of time since relativity is the one that changed how we view time.When SI-Unit for Time was introduced, whether that definition "the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom" preserved fully (ie:quantitative vs qualitative) the nature of time (and its impact on other accepted theories) is an interesting discussion that some still consider an open one after SI unit was published. Whether that was a finished discussion, or was an abandoned discussion, is unknown to me. So, not wanting to touch the mutability of the definition of time, I just inserted the definition, and added a jab about some experimental physics there would interesting.Second can of wormsThe other complication that I hand-waved over is velocity. Velocity alone doesn't cause time dilation, acceleration does. We write our stuff talking about velocity, (common writing about twins paradox where one twin travels and one twin doesn't travel for example), wepretend:under the cover that without acceleration you don't get velocity. But in fact, it is the acceleration that one twin must do (and the non-traveling twin doesn't) that caused the time difference.Eating up the wormsThe pretending is because the deeper one digs, the more difficult it is to explain the dirt that one digs up. So, staying with generally accepted principal and brushing over the deeper complications (while staying true to observed result) is the way around having a 100 page explanation that no one wants to read anyway. (Or trying to explain the Twin Paradox's explanation is actually wrong, it is not velocity, it is acceleration... One would be arguing with a thousand people a thousand times over.)So as long as the "light travel slower in water" matches the observed result, that's fine. But digging deeper will always uncover more interesting facts. Some of the facts may even be Nobel Prize material, who knows.

author: newbrain
author_rank: Super Contributor
timestamp: July 13, 2020, 10:58:20 am
content: Quote from: Rick Law, abridged by newbrain on July 13, 2020, 05:43:55 amI think an Oscar would have been more appropriate for Eisenstein - though they probably shared the same barber...I'm surprised that the director of immortal masterpieces such as Battleship Potemkin or Alexander Nevskij would have such insights on time and EM waves propagation!About time dilation, it can be promptly experienced by anyone watching his movies...On a more serious note, the two minutephysics' videos below are a good explanation of the twin paradox, and why velocity isnotthe cause of the elapsed time difference when the twins reunite.and

author: Rick Law
author_rank: Super Contributor
timestamp: July 13, 2020, 08:36:24 pm
content: Quote from: hamster_nz on July 13, 2020, 05:41:26 amWhen in practice it doesn't make a difference, why waste resources dealing with it. So it is perfectly reasonable to ignore such differences. I do understand the different perspective here.To someone practical (Engineer), the different is tiny and can be ignored (most of the time). But to a theoretician (Physicist), when it is not exact, it is not the same.Rather like telling a mathematician to accept that 2+2=almost 4 but not exactly 4. It is kind of earth shaking.I think the main reason it bugs Physicist is:Prior to time dilation, the thought was "Time is absolute", there is a universal clock governing progression. Now we realized there isn't a "Master Clock" for the universe. The common understanding was "Space is the arena, and Time is what enabled things to happen in that arena". Time dilation, however small, shattered that idea.Coupled that with Heisenberg's Uncertainty Principal, Planck's discovery of Planck's Constant (which kicked started Quantum Mechanics), wave-particle duality... Those earth-shaking discoveries and theories threw the proverbial monkey wrench at the foundation of the Physics. Physicist before that time frame thought they knew how the universe works, just the tedious job of tidying up loose ends left. Today, it is hard to find a Physicist who would say they fully understood how the universe really works."If you think you understand quantum mechanics, you don't understand quantum mechanics." Richard P. Feynman.No, we really don't know what is going on here... Some theories seem to work, but they don't all work together with each other. They just work within their domain. It is a fascinating but frustrating universe we live in.

author: free_electron
author_rank: Super Contributor
timestamp: July 13, 2020, 08:58:23 pm
content: nope. much faster. an hour of scubadiving always feels it's over waay too fast ...

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2020, 10:59:12 pm
content: Charged particles all have mass, and therefore must travel slower thanc, the speed of light in a vacuum. However, when a massive charged particle has a velocity higher than the speed of light in a dielectric medium (such as water or gas), the result is called Cherenkov radiation, seehttps://en.wikipedia.org/wiki/Cherenkov_radiationwhich is named after the Soviet physicist who discovered it. It is somewhat similar to the shock wave produced by an aircraft traveling faster than the speed of sound in a medium ("sonic boom").

author: cliffyk
author_rank: Frequent Contributor
timestamp: July 14, 2020, 03:35:45 am
content: I had a friend some years back who felt quite strongly that time travel was impossible. I told him "Nonsense we are doing it right now, we just cannot (yet?) control the velocity and direction."

author: GlennSprigg
author_rank: Super Contributor
timestamp: July 15, 2020, 12:06:10 pm
content: Quote from: cliffyk on July 14, 2020, 03:35:45 amThere's the old conundrum, regarding someone saying that "Maybe we can travel back into the past, becausethat's already happened, but not into the future". However, it then goes to the 'logic' that if we went back intothe past, we would meet people that would see US come from THEIR future! It can't only work one way...P.S. Your photo at the bottom of your post, reminds me of the 3D 360-deg '.HDR' image files!!See the free software/viewer link below, which doesn't even need to be installed...https://www.lizardq.com/en/viewer/And some example .HDR files to use, from...https://www.lizardq.com/en/sample-images/All created from the 2D .JPG representations. Quite interesting!!!

author: cliffyk
author_rank: Frequent Contributor
timestamp: July 17, 2020, 07:23:02 pm
content: Quote from: GlennSprigg on July 15, 2020, 12:06:10 pmIt's a built-in image stitching function of an old (10-12 years?) Canon Elph I keep in the shop...

author: StillTrying
author_rank: Super Contributor
timestamp: July 17, 2020, 08:17:11 pm
content: Quote from: GlennSprigg on July 15, 2020, 12:06:10 pmYou're forgetting there's an infinite number of universes.https://www.ranker.com/list/time-traveler-pictures/ashley-reign