When I first learned about this in college it really really bothered me. (obviously it still does to some extent)
That time is not constant on a scale that lets us measure it from space vs the earth much less from upstairs to downstairs is somehow deeply unsettling. If you're traveling at 10 m/s as you go out of the gravity well you go faster and faster because time speeds up, but your velocity per unit time stays the same.
Something that is really hard for my brain to wrap around in any meaningful way.
During some radio work this became actually a thing in that if you're doing time-of-flight measurements of originating RF energy and one receiver is in a platform flying above and one is on the ground, at high time resolutions you start having to correct for difference in the rate of time. This is definitely something you have to do if you want to get really accurate time from GPS satellites. So freaky it hurts.
PBS SpaceTime has a treatise on relativity. There are a dozen videos worth watching on this topic alone. The video about “the speed of causality” is the one that caused me to level up:
It didn’t bother me so much when I finally understood that the duration perceived by an observer is simply equal to the path integral of distance along their worldline.
When you think about it, you will realise there’s almost nothing else it could reasonably be.
To figure out how far a distance you traveled to get to my house, I need to know which path you took.
To figure out how long a time you traveled to get to my house, I need to know which path you took.
Our ordinary intuition is instead,
"To figure out how long a time you traveled to get to my house, I need to know the time on my clock when you left and the time on my clock when you arrived."
But that turns out to be wrong if you care about a high degree of precision or if you were traveling very fast.
Might be reasonable, but it means that comparing timestamps between two observers requires knowing the observers' entire history back to some reference timestamp no? Still a headache.
Also, if we added the speed of light to an object's speed you'd get really weird results like you'd see a car coming towards you before the car actually arrived.
Trying to stay alive in such a world would be quite a challenge.
How do you feel about it vs leap seconds vs leap smears? I really wish timestamps were tied to TAI instead of UTC time (and therefore subject to leap seconds).
> If you're traveling at 10 m/s as you go out of the gravity well you go faster and faster because time speeds up, but your velocity per unit time stays the same.
You seem to be confusing coordinate time with proper time. The time you experience as you get out of a gravity well is proper time, which, as a sibiling comment said, is something you obtain when you do the path integral of the path you travel. This time is not exactly affected by dilation. Anything traveling with you will not have its time go faster or slower. Anything that is not traveling with you, say stationary on Earth, will indeed have its passage of time shifted with respect to you.
Coordinate time is the time observed by an observer at the center of the gravity well, looking at you (not always, but generally so for most calculations. Also, observer = origin of frame of reference) and that is what is morphed and bent around. Since you're an observer as well, you also see other points experience time differently, since from your point of view, they're moving away from you.
That really depends on what you mean with real thing, I would say our understanding of time and space is heading towards them being emergent phenomena and not fundamental ones. As far as we know, there is no thing in the universe called the time that you can just measure, you can only look at the ordering of events. And then we invent a variable called time that lets us express the laws of physics reproducing the observed events in a simple way, but that is much more a convenient mathematical and everyday tool than a real thing than one usually realizes.
Time is absolutely a construct, just like the iPad I’m typing this on is a construct. I really can’t be sure it exists, but the model I have in my head that I’m tapping on a large flat surface with my fingers agrees with my observations. If in my next tap I get a painful burning sensation in my finger and I hear the fire alarm go off I may need to change my model to consider that I was mistaken and I may be touching a what appears to be a flame instead.
Is it that digits are prohibited or that four digits followed by three letters is prohibited?
When that photo was published, WA was still running sequential plates as three digits followed by three letters; since then, they ran out, and they chose three letters followed by four letters. When that runs out, they will most likely switch to four numbers followed by three letters, so it makes sense to reject personalized plates that match the future series of sequential plates.
So... Over a quadrillion times per second? I don't get why people do this. Stephen Hawking did the same in his book ("X star is over a million million million million miles away"). Just give me the number straight. Breaking into millions of billions of trillions just makes it more confusing as I try to consolidate orders of magnitude.
I go the other way. I think if we started telling people that Jeff Bezos was worth two hundred thousand million dollars [0] more of them would say, what the fuck?, that’s disgusting.
The b in billion has become meaningless. Nobody has anything to anchor it to.
After a thought experiment I was able to determine the meaning of "billion":
- It can be said that there are one thousand million (1,000,000,000)
- It can be said that there are ten thousand million (10,000,000,000)
- It can be said that there are one hundred thousand million (100,000,000,000)
But it cannot be said that there are a million million (1,000,000,000,000), it is said that there is a "billion".
- Then, there may be a million billion (1,000,000,000,000,000,000)
But there cannot be a billion billion (1,000,000,000,000,000,000,000,000), it is said that there is a "trillion"
- Then, there may be a million trillion (1,000,000,000,000,000,000,000,000,000,000)
- There may be a billion trillion (1,000,000,000,000,000,000,000,000,000,000,000,000)
But there cannot be a trillion trillion (1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000), you say "quadrillion", and so on...
Translating this with the google translator has been hell, every time I typed "one thousand million" and "million x" it translated into "billion", and every time I typed "billion", it translated into "trillion".
I just skipped the sequence: one thousand billion, ten
thousand billion, one hundred thousand billion so as not to lengthen my comment and I did it by jumping to the millions directly.
Google translator makes a creeper with the "billions", read my comment in english.
This article reminded me of true atomic wristwatches [0]. If precision gets good enough one day, you could get a synced pair and give one to a friend and compare after the years who has relativistically aged faster :)
Stand-up Maths did a really good (and quite self-deprecating) video of both the Special Theory of Relativity the General Theory of Relativity and how they explain time dilation that helped my brain make sense of what it was having a hard time understanding.
I've had people incredulous at time dilation effects in relativity. I give them the example of this having been directly measured in the 70's. There, they put one clock in the lab and another on a jet and flew it around a bit.
There is something about weed that can slow down time, but your ability to learn is hindered too. Question is, how to slow down time and be able to learn a language overnight..
You guys are so boring. I was referring to a joke which tells that when science discovers a way to extract energy out of irregularities in spacetime manifold, the reactor would still boil water to make electricity.
Remember how there was a thought experiment where you couldn't tell the difference between accelerating at 1G in an elevator, or being in a 1g gravity field?
If the elevator is more than a few CM taller than the clocks, now you can. Bolt one to the floor, the other to the ceiling.
If they run at the same rate, it's 1g acceleration. If there is the predicted difference, you're in a 1g field.
Nowhere, i.e. if you are in the falling elevator the tennis balls will fall downwards if it's uniform but any real gravitational field (apart from something of infinite radius) will make them converge gradually towards eachother as they fall towards the CoG
Nowhere in the real world, but that’s okay since we are dealing with thought experiments. An infinite plane of mass is roughly what you’d need so that the contributions of each element add up to a uniform field.
Nowhere. Gravity is just inherently radial. (But if you have a very large spread it can look fairly uniform, of course. Especially if your measure of “flat” is actually curved to the same radius.)
That time is not constant on a scale that lets us measure it from space vs the earth much less from upstairs to downstairs is somehow deeply unsettling. If you're traveling at 10 m/s as you go out of the gravity well you go faster and faster because time speeds up, but your velocity per unit time stays the same.
Something that is really hard for my brain to wrap around in any meaningful way.
During some radio work this became actually a thing in that if you're doing time-of-flight measurements of originating RF energy and one receiver is in a platform flying above and one is on the ground, at high time resolutions you start having to correct for difference in the rate of time. This is definitely something you have to do if you want to get really accurate time from GPS satellites. So freaky it hurts.