This argument, as far as I know, relies on the nature of time dilation. You see as your velocity increases closer and closer to the speed of light, time itself begins to slow down. This is not an analogy or some fancy math trick, this is a real thing you can measure in the lab. As you get closer and closer to the speed of light time slows more and more. Such that as you reach the speed of light (again this is physically impossible at least for anything with mass) you can think of time as stopping. So for light or anything that moves at the speed of light they’re kind of isn’t such a thing as time, but I digress.
So (again even though it’s actually impossible), what happens as you start to go faster than light? Does this trend continue? If it does that would mean that time starts to reverse. And once you see that faster than light travel might imply time reversal, it should be easier to understand how this would violate causality. Because how do you get event A caused by event B when event B was before even A?
Say a ship leaves Earth traveling half the speed of light, but it carries a communication device that can communicate with Earth “instantaneously” (i.e., faster than light). From Earth’s frame of reference, time on board the ship is slowed down by a factor of 0.866, while from the ship’s frame of reference, time on Earth is slowed down by the same factor. (This isn’t some trick of perception—the geometry of spacetime distorts in such a way as to make both these observations true simultaneously.)
Now suppose a year has passed on Earth, and we use the device to communicate with the ship ”instantaneously”. From Earth’s frame of reference, the ship has currently experienced only 316 days of elapsed time, so that’s when they receive the signal according to their clock. But from their frame of reference, Earth at that point has only experienced 274 days of elapsed time—so when they send their “instantaneous” reply, it arrives on Earth three months before the original signal was sent.
From Earth’s frame of reference, time on board the ship is slowed down by a factor of 0.866, while from the ship’s frame of reference, time on Earth is slowed down by the same factor
Why is time on earth slowed down from the ship’s perspective? Shouldn’t it be faster? Like if earth perceives that the time on the ship is passing slower shouldn’t the people on the ship perceive the time on earth as passing faster to compensate?
Also, I have quite a hard time understanding how time exactly slows down. Is it sort of as though we adjusted the time step duration (tickrate, more precisely) of a physics simulation in an area (making everything happen slower/faster there in relation with the rest, where the original timestep is kept)? (Without losing precision and all those problems that occur in a simulation normally) Or is this analogy flawed and that is why I’m not getting it?
Why is time on earth slowed down from the ship’s perspective? Shouldn’t it be faster?
According to special relativity, all non-accelerating frames of reference are equally valid, so the observations are symmetric: both Earth and the ship see the other moving away at 0.5c, so they both see the other slow down.
Now it’s true that if the ship turned around and returned to earth at 0.5c, it would be the ship’s clock that was behind earth’s, and not the other way around—but that’s because, when the ship turns around, it accelerates, and while it does so the whole non-accelerating frame of reference thing goes out the window. After it finishes turning around, the point in earth’s timeline the ship judges to be simultaneous with its own will have jumped forward in time—so that even though it observes earth-time moving slower than its own during both the outbound and return trips, the time jump as it turns around will more than compensate.
(Or equivalently, you could say that after turning around, the ship observes its own past history on the outbound trip to have been slowed down even more than earth’s.)
Okay. Thank you! This explanation made it click for me (now I think I get the original example too). Here the real cause of the violation is the instant communication, isn’t it? If the communication was done via radiowaves (which as far as I know also travel at the speed of light) it would not be violated, because of the time it takes for the information to arrive from the Earth to the spaceship and back, is that correct? Is this why (as I have read/heard on several occasions) the upper bound for the speed of information is also the speed of light?
When I say the parties observe each other slowing down, or observe the simultaneous point in the other’s timeline jumping around, they don’t observe this in real time unless they’re using faster-than-light communication. Using conventional means, it’s only after receiving the signals and compensating for the redshift or blueshift that they can reconstruct the other’s past timeline relative to their own.
Has anyone actually proven no violation of causality? Wikipedia seemed to suggest that it’s not physically impossible to have a wormhole, take one of the ends on a round trip so that it doesn’t age as much, and you’d be left with a situation where you can go in one end and come out in the past.
My partner is pursuing their PhD in Philosophy and studies history and phil of science and has dealt with this question a bit, so I’ll take a stab from that perspective.
My answer will rely on the possible worlds framework (a la Lewis) along with a tiny bit of knowledge about Newtonian mechanics.
Is it possible to imagine our world with different physics? Yes. Prior to discovering special relativity and quantum effects, we had newton’s Classical Mechanics, which was able to precisely and accurately describe and predict the movement of bodies in Euclidean space. So, if we can imagine our physics without the complications of curved space and quantum effects, we can imagine our world with an alternate physics that has been somewhat rigorously tested.
Additionally, we can easily imagine the world without the curvature of space and quantum effects (which should be clear by the fact that it’s not too long ago that we thought that was the best picture).
Classical Mechanics offers a working physics that just didn’t turn out to be correct in our (curvy) world. However, relying on the possible world’s framework, it would be easy to stipulate a possible world where Newtonian mechanics was true, or even a possible world where physics shifted from one set of laws to the other.
If we believe the evidence that physics could be otherwise, we might conclude that the laws of physics are relative to a world and a time (and, importantly to metaphysicians, not more fundamental than those two things).
I think a working physics lacking space-time or motion might be impossible to imagine.
We are all very likely doing it now with most of what we believe to be the laws of physics. While they may seem to reasonably explain the phenomena we have been able to observe that represents such an infinitesimal fraction of the universe that the margin for error is astronomical.
I check Lemmy about twice a day, work in and foster a collegial environment, and have a background in science. I can’t say I would be intensely active, but currently there is less than 1 post per day here, so even a little would lighten the load.
/r/askscience was one of the highlights of Reddit - I’d love to help establish a similar community here in /c/askscience. I especially liked that posts and followup questions were rewarded for being inquisitive, and that off topic/inaccurate responses were removed. Posts on topics I’m familiar with were filled with scientific information, and I learned a lot from posts on topics outside my area of expertise (also the ones in my area of expertise, to be honest).
I have a science background (nuclear physics) and lots of experience communicating with remote collaborators. I’m fairly active on lemmy (on another account, I created this one to be my semi-professional one) and would generally have no problem checking the site at least 3 times a day. And I have no issues with mod coordination over Discord.
Let me recommend the books by Greg Egan. Essentially, he takes some basic premise of our universe’s physics, twists it around, and then writes novels exploring what living in such a world would be like. Superb. You can check his website for an idea, but don’t be scared by it. He drops all the physics and math in there, but the novels shy away from that and use metaphors where absolutely needed.
Dehydration can lead to death through mechanisms such as organ failure, blood thickening and reduced blood pressure, electrolyte imbalance, brain swelling, shock, and build-up of cellular waste.
Electrolyte imbalances and upset balance of salts and sugar can cause impaired cellular function, heart problems, neurological issues, kidney damage, and shock, ultimately leading to death.
As water level decreases, the total amount of sodium stays the same. So, essentially it is increasing in concentration. Too much salt interferes with heart cells’ ability to contract together. So less water = more salt = less heart coordination.
Cardiac arrhythmia due to hypernatremia and hypovolumenia can be fatal. There are many changes that occur, but the effect on the heart will kill ya.
Hi there. I’m interested. I’ve also got a science background (life sciences), it’s my job to communicate well, and I’ve been working remotely on a distributed team for years now, so I know how important communication and coordination are. I’d love to help foster an inclusive and informative community, and I can check Lemmy pretty frequently (multiple times a day). I’m okay using Discord. (I’m already on Slack and Telegram basically 24 hours a day, so it’d be great if that were the tool of choice, but Discord is fine, too.)
Salts are absolutely necessary for ordinary nerve- and muscular function. If you’ve ever sweated a lot without eating or drinking some salt solution you would notice your muscles start twitching, vibrating and cramping. After a while you can also notice getting light headed and blurry vision.
Source: Been in situations with plenty of water but no salt, and enormous amounts of sweat. Been in the same situations with access to salt for comparison.
That’s a very incorrect statement. NaCl, KCl, and MgCl2 are essential for our bodies to function appropriately. If you are working out for an hour or mowing the lawn on a hot day, you are mostly correct. You can replace the lost salt though a balanced diet. If you have sustained sweating, such as when you run a marathon or play a match of football, it can be deadly to not replace these salts.
In the vast majority of cases, people don’t need salt when they exercise. You just described a fringe case that virtually no one experiences. You high school football coach shouldn’t be giving you salt. That could be dangerous. They should be giving you water.
The coach won’t be giving them salt directly, but will always provide a sports drink which contains salts.
Ever watch any sport and a player falls over with a cramp? They have drunk too much water and not enough electrolytes.
Here’s a study from one hospital in Oslo, Norway. Norway is not considered a hot region of the world. Between 2010 and 2015 they treated 31,000 patients in the ER from a population of 135,000 for electrolyte imbalance. That’s roughly 18 patients a day. This is not some sort of fringe case.
Your bladder and kidneys need water to function. Initially, your kidneys slow sending water to your bladder which is why your pee turns dark. Then you start losing water in your blood to keep organs functioning but the decrease in blood volume causes your blood pressure to drop. This makes pumping blood increasingly difficult for your heart so your body will start sending less blood to your organs. This starts damaging all your organs and eventually your kidneys stop filtering your blood. Toxins build up in your brain that’s already not getting enough blood and eventually shuts down and you die.
Copper metal "dissolves" in nitric acid (HNO3). Actually, the nitrate ion oxidizes the copper metal to copper (II) ion while itself being transformed to NO2 gas in the process; the copper (II) ion then binds to six water molecules.
It looks like you are using this one: ArctiClean 1
Which seems to be specifically made for this application and supposedly consists of “citrus and soy based solvents”. Aluminium is solved by highly acidic (like sulphuric acid) and highly basic (like sodium hydroxide) solutions. Which it really doesn’t sound like until it somehow broke down in a way it got more potent.
Was it maybe a specific thermal paste with a metal like mercury or gallium inside? Supposedly they can quickly dissolve aluminium. Of course, I don’t know what happened but maybe it was dissolved by the cleaning solution and then rapidly reacted with the Aluminium of the heat sink. If so, that would still make me wonder about the bubbling and foaming when the cleaning solution comes in contact with the left overs.
I would assume that nobody makes thermal paste out of anything terribly reactive, but… That .gif looks like something out of a NileRed video.
IIRC, gallium makes aluminum get super brittle, which might cause it to crumble like that; but the foaming makes me think that the heat sink might have managed to oxidize all the way through, and it’s aluminum oxide reacting with the cleaner.
I can’t get your images to load, but to me, a materials chemist, it definitely sounds like you’ve managed to dissolve the aluminium and copper by using an acidic solution. Presumably, the cleaning solution contains some electrolyte that should help dissolve oxides, but if the solution is corrosive enough to oxidise the aluminium and/or copper the electrolyte will make the reaction more aggressive by rapidly dissolving the protective oxide layer as it is formed, such that the aluminium/copper is further corroded.
To be fair, this is just speculation based on what I’ve read here. I could maybe give a better analysis if you let me know what solution you’ve used, and what the heat sink/paste were made of, and if I can get the pictures of the resulting product (“ash”) to load.
This seems brilliant, I wonder what will be the efficiency of such system, it seems like it could almost power itself as long as you supply it with salt water (and have the Fresh water column outlet lower than the inlet). What am I missing?
Hi, could you expand on your question (or questions) in the main post? The more clear your questions are, the easier it’ll be for someone to address them. Thanks!
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