Time Stops at the Speed of Light. What Does that Mean?
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- เผยแพร่เมื่อ 2 พ.ค. 2024
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You might have heard that according to Einstein's theories of special and general relativity time doesn't pass for light, or that time actually stops for light. Can this possibly be correct? In this video, I will look at what the maths says and discuss what it means.
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#science #physics - วิทยาศาสตร์และเทคโนโลยี
This video comes with a quiz which you can take here: quizwithit.com/start_thequiz/1713615419870x520177431082434560
Why not travel fare back in time as time is moving forward
Space Time diagram: ASSUMES both space and time change at the same warped rates. (Which they probably do not).
I want to both compliment and chide you for this video. Your general explanation was good however you did a disservice to reader: Time does not stop. Time equiibrates to space.
1 Time unit equals the space unit traversed 1
Therefore
Tan^-1(1/1) =45 degrees
2:15 " ... coordinate time is physically meaningless"
6:42: "... coordinate time [that] describes the universe we inhabit"
Now I'm confused.
I want to both compliment and chide you for this video. Your general explanation was good however you did a disservice to reader: Time does not stop. Time equiibrates to space.
1 Time unit equals the space unit traversed 1
Therefore
Tan^-1(1/1) =45 degrees
Light: "I'd like to respond to your question, but I simply don't have the time!"
Light: "I'll take a potato chip.... and eat it!"
I thought you have all the time in the world! 🤷♂
I was born in the sun. But before I had time for anything, I was already here in this detector. Now I'm no longer light, I'm now just the heat I imparted.
I lived for zero seconds 😢
@@treeinthewood It's all relative....
😂😂
A photon checks into a hotel and is asked if it needs help with its luggage. It responds: "No thanks, I am travelling light.".
Well done! 8 out of 10
@@jonathangehman4005 A photon's wife tell's him to fix the leaky faucet. He tells her he's got no time.
wow...😮
Why didn’t he just say he didn’t have the time for it?
Receptionist: Mr.Light, here's your key, your room is...
Light: I'm checking out.
Quantum Bell boy: I'm having and not having your luggage.
I don't think I've ever heard this particular relationship between light and time worded so well. Thank you.
"I have always been everywhere I am."
- Light
From the perspective of the photon, it is absorbed the moment it is emitted.
which would imply that, from the perspective of the photon, it never existed.
@@3rdPartyIntervener Not much of a retirement plan...
Also, from the perspective of light, space doesn't exist. No perceived distances, as it happens all at the same instance. So, no space, no time for light. Those things are reserved for us mortals. It's crazy....
do any photons really travel at "c", tho? I mean at 1 Hydrogen atom per cc in space, then the index of refection minus one is ~1/2N_A (Avogadro's number) ..and that is NOT zero, so v is zero point 9 [24 times]....for a time dilation of ~ 10^24 < infinity. or a 1 ms delay of the CMB photons. Small, but not zero.
The photon can be involved in just two events which it perceives as being simultaneous, one which emits it, and potentially another which absorbs and destroys it.
In the heat death of the universe some photons will never be absorbed and persist in a kind of limbo for eternity, which thankfully they will not be aware of anyway.
TH-cam's FINEST deadpan humor. Don't ever change, Sabine!
@@imilliemedina666 ... then her husband would be quite perturbed. :)
I am definitely looking for a way off the planet 😆😆💿
"last time I checked TH-cam didn't support 4-dimentional graphic" - this is gold
Perhaps just as well, given the amount of data it would take. A 256*256*256*256 object would take 4.2GB, if each hypervoxel was just one byte.
Not even 3, technically.
Speaking of Time stopping for a Light, I once travelled with my boss to a small town in northern Michigan, which had only a single stoplight at the corner of Walk and Don't Walk. He was driving the rental car to the only restaurant in town and accidentally ran through the only red light in town and was immediately pulled over by the only Sheriff in town and handed a ticket.
And I always thought proper time was when one had to wear a tie.
Proper tiem
@@mikeycomics Proper item
@@yourguard4Proper tie 'em
I always thought proper time was using 24 hours instead of 12
These lowbrow pun comments representing how superficial this channel has become
Proper time - like tea and cake time
Half past 3: 00 to be specific☕🍰
and proper food - cucumber sandwiches and fruit cake
Yes, but proper tea is theft (Apologies for the old socialist joke)
Lunch time.
@@danielcomeau9880 Time is an illusion, lunch time doubly so.
I think that the confusion for many of us non-physicists about timeless light arises from the common application of time based parameters to that light. Take Blue light for example: Say it has a frequency of 600 x 10^9 Hz, or (times per second). If a photon of that light travels for a light year in distance for a 'stationary observer' at it's destination. How many "times" has that light 'pulsed'/ vibrated in its travel? From the observer POV, it has vibrated maybe 1.9X10^22 times over the year. But if time has stopped for the light, then it's time clock cannot allow even one pulsation during the journey. How then can the concept of 'frequency' be applied to a photon of any em radiation? Or is this another of those things like "spin" for an electron (which is not "actually" spinning..)?
In this case, from the photon's perspective, the photon would be one long wiggly line rather than a particle moving over time.
Good question! The frequency of a beam of light is defined by the number of cycles that pass a fixed point per second. The notion of 'a fixed point' and 'a second' are both with respect to the observer's frame. The frequency will be different as measured in different reference frames. The waveform of a pulse of light however is a fixed shape that moves through space and as it moves the 'wiggles' pass an observer at a given frequency. Since the waveform doesn't change as it moves it *is* like the state of the wave is frozen or fixed.
@@tysonprice5058 I am trying to picture it! One point though: Not only does time stop but also distance shrinks (to zero - for the photon). In that case, the frozen wave has effectively no crests or troughs, it is in fact acyclic!
I think it’s bizarre that a radio transmitter can emit a weak signal, yet a simple, small receiver can pick it up hundreds of miles away. It can’t be explained by a model of radiating discrete photons, but by fields which crystallise into photons when observed. Anyone care to explain the actual physics of it?
Well, you could consider a zero point field to which may travel into, or another perspective may be that photons aren't zero, but infinitesimally small, as in approaching zero by some order of Plank time or something
Personal perspective of time: Your brain speed isn't constant. It's faster when in your youth and slower in your elder years. When your brain speed is high, your perception of time is that it is running slower, and the opposite for when your brain is running slower. This variability can happen within a day also, your brain speeds up during an accident and people report that time seemed to slow down. It's almost like there's an internal calculation of how much information is being consumed by your senses relative to actual time and the resulting perception is not that the amount of information changed, but that time changed. The next step would be to look into how you can exercise your brain speed function and force it into a faster mode so your personal perception of time slows down, which would be quite nice
Light says, "hello."
Hello! Thanks for checking in!
How did you find the time?
Can you go over the Stress Tensor, Quantum Mechanic, and Hawking Radiation issues of a FTL Warp Drive? Never fully understood those.
@@BerndFelsche Talking is a free action, of course.
So many in the comments believe light doesn't have time to say, "Hello." I haven't found anyone yet who witnessed that, but people have claimed that it WAVED. 👋 @SabineHossenfelder
Fascinating topic. Please explore this deeper
An excellent presentation! I think I finally have a grip on "grip on proper time". Thanks Sabine!
I feel dumber having watched this
These visuals helped me: th-cam.com/video/Rh0pYtQG5wI/w-d-xo.htmlfeature=shared
😂 same
That realization makes you smarter.
I always feel dumber watching this.
Count me on😂. Some things are obvious and some can never learn. It needs smarter person...😟
Light here, I'd love to help you but I don't have time.
This comment was posted seven hours after the original comment: Light here, I’d love to help you but I don’t have time. It had 51 likes as of time of writing.
@@gregoryturk1275 I guess you are referring to the similar post by @sleightofmind2016 7 hours ago, Light: "I'd like to respond to your question, but I simply don't have the time!" I looked when I posted this to see if anyone else had already said something similar, and I didn't see his comment, but the joke does rather suggest itself, so I'm not surprised. It looks like they were posted around the same time.
@@crawkn There was another comment just like this one? I didn’t know that😅 I just commented that because sometimes people edit their comment after a few months and all the replies make no sense.
@@gregoryturk1275I just spent way too much time looking to see which one was posted first, and it was mine, but the other one got more likes and comments 😢.
@@crawkn That sucks :(
Thanks Sabine, love your discussions (and brilliant humour and presentations). I have a mental block accepting that time stops when travelling at C (but really only for an imaginary traveller, since Photons cannot have mass, i.e., watches) for a couple of reasons:
1) if time stops @ C, then the photon cannot experience freq or wavelength, then this means that only an outside observer sees the "wake" of a photon propigating electromagnetically across a distance and the photon itself (from it's POV) did not act on the space it travelled through, i.e., no fields; ...and suprised Albert let that fly... "you saw me propigate, but I didn't do it even once"; and, 2) Time is relative, so we can wrap our heads around each observers passing of one second being relative, allowing us to reconcile the different passage of time of someone on Earth while waiting for someone to travel to Alpha-C & back @ C....but estimates are that the person returning from from Alpha-C will have aged ~9 yrs (or whatever that estimate is), while everybody on Earth are dead or robots. Overall, if time stops @ C, a photon can go to the [pretend] edge of the universe and back and not experience passage of time....I think the photon needs to be given a little more credit for all the propigating and undulating it takes to go from a to b.
I would appreciate if someone can point out any misinterpretations I might have...and maybe it's in the title "Speed" of light, not velocity of light. I think Space-Time might be missrepresented, possibly where the path travelled (from x,y,z to x1, y1, z1) is definable (some constant), time is relative to the persepective (POV) and space is its own thing and not related to coordinates, but rather possibly to energy/field/matter density. Just a thought, which will probably get me a some "opinions". Thanks again!!! I really enjoy these discussions and these presentations.
As usual Sabina, you helped me place the last piece of an image if understanding. Thanks great vid.
5:30 I'm disappointed there's no Light Yagami comments here :(
I was also looking for any. Only found yours, but that's still a win.
Such intellects:)
There's a Light Yagami reply in the first comment
Light Yagami will probably boast "I'll kill you in no time!"
5:30 I think Light is too busy with the death note to reply
😂👌
And eating potato ships
You explain well Sabine. Very agreeable and clear. A true talent you got there.
Cheers.
One explanation/clarification I've been very grateful for is that everything always travels at the speed of light - it's just that somethings (e.g. us) travel mostly in the time direction of spacetime, and somethings (e.g. photons) travel entirely in the space direction of spacetime.
the time direction in this case just means permeating bounded energy (e.g. Quarks oscilating at the speed of light because they are not moving), and the space direction means permeating free energy(e.g photon). one thing no one mentiones is that energy at the quantum level is always moving at the speed of c, the only difference is wether it is bounded or free
@@stefan24georgiev the channel float head physics is far superior in explaining this.
Is there any empirical evidence that everything always travels at the speed of light, or is this just some "thought experiment" contrived by a theoretician?
@@NondescriptMammal Yes it has been proven.
@@NondescriptMammal 'We all move at speed of light through spacetime'.. What does it really mean?
FloatHeadPhysics
149K subscribers
"If you're interested in space travel and.. who's not interested in getting off the planet at this point?" 😂
Never change Sabine, never change! 😁
Asians seems quite happy with how things are developing. I wonder why.
Only if you live in Germany .... 😁.... or the USA ... they are almost there where Germany was in 1940......
@@thechessmaster9291 in what sense? Going crazy with socialism?
Amazing line!
@@HR-yd5ib Just stop shoving your politics into everything 🙄
I have always admired you, Sabine!!! Love your work!
For tge first time in my life, I understood the spacetime diagram. Your comparison of the Euclidean and Lorentz equations was really crucial. The effect of that negative sign in the Lorentz expression , so important.
Thank you for the video.
Good description. I always like summarizing relativity by saying that everything is always moving at the same speed through spacetime, even light, so if you're stopped in space then your speed through time is maximal, and if you're moving at the speed of light through space, your speed through time coordinates is zero. Kind of like a conservation law of speed through spacetime. Though this doesn't account for the subtlety of proper vs. coordinate time.
It's not a bad way of thinking about it. The only subtlety is that all inertial reference frames are equivalent, and so who is traveling how much in which direction is relative. Everybody in an inertial frame experiences themselves as moving 100% in time, 0% in space, and everybody else as having a different mix. These all turn out to be valid descriptions of the universe as long as you transform properly between different frames: no frame is privileged at a fundamental level.
@@jameshart2622 If you are travelling through space, you are through less time... if you want to think one can 'travel' through time.
Same. But I think of it as if we’re travel through different timezones. As each of the ‘fabric of space’ has its own local time, the faster I go through space, the less of the ‘local time’ I experience. But my internal clock always ticks the same.
This also helps me make sense of time dilation by gravity as a non physicist. Because according to relativity, me standing still on a planet pulled by gravity is equivalent to me accelerating upwards at constant speed, therefore, it’s no different than me moving through space even I’m standing still. The stronger the gravity = faster I move = less of the local time I experience = my time slowed down from outsider perspective.
"Kind of like a conservation law of speed through spacetime"
Indeed. This explains (some of) the length distortion we see with speed: it's the same effect as refraction. The speed at which light propagates inside a medium differs from one to another. Replace medium by reference frame.
"Though this doesn't account for the subtlety of proper vs. coordinate time."
But if you think proper time as quantity of interaction, then you may got it. The more movement there is, the less interaction there is, and the slower proper time seems to pass. Coordinate time is just a convention used to obtain the proportion of movements to interactions/proper time.
I asked this very question on Reddit, to the effect of “is there a place that is moving at the slowest speed relative to everything else, and therefore experiencing maximum time”
They said it doesn’t work like that
First, thank you Dr. @Sabine for this clear presentation. Much appreciated.
Next, I have a request, as per your request at the end of the video.
Can you please make a video on super clear explanation of, "someone traveling at light speed aging slower, a.k.a time dilation."
It sounds illogical or perhaps its interpretation.
I mean:
- Suppose there is person A and B on the earth.
- Somehow person A has the ability to move/travel at light speed.
- Person A takes off from the earth to some point in outer space, for precisely 1 second, and then returns in 1 second. So 2 seconds has passed for both person A and B.
- Why then does "time dilation" say that in this case person B will have aged so much more than person A (when person A travels to and back at light speed), yet the "moment" that has passed for both of them is 2 seconds?! It sounds illogical both rationally and mathematically.
I feel this concept is one of those which has also been misrepresented in interpretation to the common person, just like the one you have explained in this video, as well in your other video debunking the misrepresentation of Einstein's interpretation of "entanglement" and "spooky action at a distance."
Thank you in advance.
I have a different hypothesis that goes beyond relativity:
There is only ONE fundamental law of conservation, everything else is a consequence of it: conservation of causality.
Speed of light is, more or less, a random, but constant number, like 1/137 (fine structure) or h, but in this hypothesis the whole relativity is actually an epiphenomenon of the law of conservation of causality.
If this is true this has two consequences:
a) The Universe is simpler than we currently expect
b) FTL travel and communication would be possible and even relatively easy as soon as someone figures out a method / apparatus / idea of how to prevent closed timelike curves (if such a thing is possible)
With current developments like "particles under certain circumstances act as if there are two dimensions of time", etc... it's not THAT far fetched.
I've always had a question about a story I heard about Einstein and Bohr discussing the nature of quantum physics. Einstein asked Bohr if he could not observe the moon, does that mean the moon does not exist. Bohr countered by asking if Einstein could prove the opposite: how can you prove the moon exists without observation of some kind? This led me to think about locality. If i continue to directly observe the moon, but then move backwards away from it until it is so small from my perspective that my eyes or my scientific instruments cannot detect it, does that mean quantum physics depends not only on the act of observation or the observer but also on locality or the relative position between the observer and the observed?
Do you have to prove the existance of the moon for it to exist? Does the moon not exist until the moment that you've proved it? The moon does not care about wither you prove it or not other than the effect of any interaction you might have with it
The moon doesn't really exist anyway, it's just a bunch of atoms that happen to be clumped together and our brains call it a moon to make sense of it.
The real question is, can you prove the existence of all the quarks and electrons in it?
@@Loreroth It was an analogy for measuring quantum particles, where the act of measurement affects the outcome (see double slit experiment). But if the analogy holds, then it would imply a locality constraint as well.
Yes, observation and locality do affect the observation according to current Physics. See double slit experiment, although it’s not a completely settled theory.
@@richb2229 But if locality does have an effect, doesn't that imply a connection between space/time and quantum physics, and if so, isn't that a big deal? I don't recall ever reading about a double slit experiment that incorporated variable distance from the observed particles and whether it had an effect on particle/wave duality.
Gravitational waves also move with the speed of light.
Though no one knows which kind of particles they are built from
Other than time standing still for light, space also dilates infinitely for it. Because to light, everything else is moving with the speed of light relative to itself. So everything stretches out infinitely, and moves with the speed of light according to light itself. So will it get everywhere in zero seconds, or will it stay where it is forever? Its speed: ∆x/∆t = 0/0, it's undetermined. It could be any number, including zero or infinity.
So maybe light is living in an alternate universe in which we - matter - have become light... or maybe we shouldn't extrapolate what happens when we accelerate to its infinite limit, because that's impossible to do anyway.
I've been trying to work out the solution to the following paradox. It's similar (and I suspect that the solution is similar) to the relativistic train going through a tunnel that's too short. Anyways...
1. You are standing in the middle of a train carriage, which is not accelerating.
2. At each end of the carriage are two clocks in perfect synchronisation
3. These clocks can be stopped simultaneously by a signal you can send using a small remote control
4. You press the button and stop the clocks, and note that the time shown on the two clocks is identical
5. Meanwhile, you're actually travelling at a significant fraction of C
6. An observer on a platform watches as you stop the clocks
7. Since the signal has less distance to travel to the clock at the rear of the carriage, this clock stops first
8. However, both you and the passenger must agree that both clocks stop indicating the same time
I can only assume that, from the outside observers pov, the clock at the rear was always ahead, when compared to the the clock at the front. Hence, the longer distance for signal to travel to the front clock allows it to catch up with the rear clock. Is this right? And what exactly is happening? From the outside observer's pov, is time running more quickly at the rear of the train than the front? That doesn't sound right, but, if not, how do the clocks fall back into synchronisation as the train slows down?
Good thoughts! That's exactly right! while the train is moving, the front and the back clock will not be synchronized as measured in the observer's frame. The clocks more forward along the train will read earlier times than the clocks more toward the rear. All the moving clocks would be measured to tick at the same rate in the observers frame though as long as they are moving at the same speed.
If you accelerate the train to stop it, the clocks might just end up unsynchronized after the train stops. I'm trying to think through exactly how that would work lol
Doing good Sabine, thanks for asking 👍
"Elementary particles don't experience time" - Oh? I learned in school that the radioactive decay of muons is an example of time dilation because the faster a muon moves, the slower it decays (on average). Doesn't that mean in some sense that muons experience time?
I think she should have said massless particles don’t experience time. Surprised that such obvious error got through.
She was glibly pointing out that elementary particles are literally not capable of experience, i.e that they are non-sentient and asking how they "experience" time in this manner is meaningless
@@myusernamehere9972 this was my interpretation as well
I'm fairly sure she meant it as in elementary particles don't have consciousness. She said immediately after "because elementary particles don't experience anything".
Basically, there's no sense in wondering what something that can't experience anything experiences, since we couldn't ever experience it ourselves.
From my pov, even if elementary particules don't experience time, they experience evolution, like us. So we shouldn't talk about proper time but proper evolution.
You said, "If you're not moving, you have a vertical line."
Impossible. Everything IS moving on the currents of spacetime curvature or the expansion of space itself. This needs to be part of the topic and how it equates.
Thank you for this question that make us thinking🙂 When elementary particles have enormous energy or mass due to the speed of light, particles are not held in place by gravity as a result. Even if people assume that particles moving "at" or "with" the speed of light are like black hole, time will not stop by itself, because stopping time means that atoms stop vibrating. Therefore, this assumption does not admit that particles will move with the speed of light. Instead, it implies that particles will cause gravity before moving "at" or "with" the speed of light, then cause the instantaneous speed and frequency of vibration to be zero.
Light here: feeling young af.
That light can brag it went across the whole universe in a split second.
But it has no time for anything. As Sabine just explained. 😊
Sabine, a question: You talk about different theories that try to tie together relativity and quantum mechanics. Could you talk about how such theories are made to begin with?
And I've mostly heard about attempts to, more or less, quantise gravity. What about approaches in the other direction?
I ask in part because this non-physicist sees the wonky-ness of relativistic time and can't help but wonder whether you can tie that to the quantum wonky-ness somehow.
'Everything happening at the same time' (for the photon) certainly seems like an invitation to ponder what exactly that actually means as it relates to physical interactions.
At the 5:40 mark: "If you move with the speed of light, then everything along your path happens in the same instant... it all happens at once". This very sentence contains the essence to explain entanglement: Photons are not processes evolving through space at the speed of light, but more like instantaneous connections between different spacetime coordinates that comply with the light speed ratio. Two entangled photons can be detected on opposite sides of the universe and at different times, but they'll be still "connected" by virtue of the speed of light, as their journeys, no matter how long or short in time, or different their directions in space, are the same instant that happens at once from their perspective. Those different paths form the same "instant at once".
This is an interesting remark, but I thought that massive particles could also be entangled. Am I mistaken? What would the explanation be in that case?
For me, that’s one of the biggest argument against light speed travel even in Sci-Fi.
From the traveller’s perspective, the moment they reach the speed of light they instantly crash into the first obstacle in their path. No time to avoid. No time to turn off the light speed drive.
But what happens for a traveller, or a photon for that matter, which is on a path with no obstacles? (Is that even possible)
You instantly cover infinite distance? And by the time you get nowhere, infinite time has passed for the rest of the universe?
It may depend on how they're moving at the speed of light. If they're pushing space around them or moving through a wormhole or a gate system, there are factors that prevent the 'must crash into something to stop' problem.
As for a path with no obstacles: that's definitely possible. The overwhelming majority of space is completely empty. The fact we can still see microwave background radiation is because that radiation hasn't already been absorbed by something else. So for at least 13 billion years, that light has been flying freely without obstruction, which is only possible if the overwhelming majority of MBR isn't being absorbed at all.
One thing to note: Assuming space expands infinitely, then there will be an effective maximum distance light can travel. Although it may be traveling infinitely, the space it will travel into will be expanding faster than it travels. This depends on how you define distance. But if you use another object the light is traveling towards as a point of reference, then once space is expanding quickly enough, the light will never get closer to the object but the distance between them will increase instead.
@@ecMathGeek oh righ. Forgot about the Hubble volume. And the microwave background.
And yes I’m aware this is only against transluminal propulsion, and not alcubiere drive or whormholes
This is what orbital charts and orbital drift charts are for. You need some kind of active monitoring of your travel path to even want to realistically utilize that technology, if it can exist
@@anthonyvargas7564 by obstacle, I’m also including your destination.
You’ll get to where you need to be, but you crash into it at light speed.
On a related topic, does time stop inside the black hole Schwarzchild radius?
Amazing and interesting. Thank you for this amazing presentation ❤❤❤
I have a question...
So as I understand it, time slows down as speed increases. But for the thing that time is slowing down for, it has no awareness of that, because any means of measuring time or being aware of time, that's also moving with the thing that's going fast is also experiencing slower time and the two cancel out. I'm probably not explaining that very well, so let's use an analogy... A space ship is accelerating continuously. After a long time, the speed of the ship approaches the speed of light, as far as the instruments on the ship are concerned. After more time, it exceeds the speed of light and continues to accelerate. It can achieve many times the speed of light, according to the result of calculating the acceleration multiplied by their time. So it's like hey we've been accelerating this much for this amount of time therefore we must be going this speed. But the timekeeping device has slowed down and so has their own awarenes of time. To them, inside the ship, everything seems normal and they are simply travelling faster than light. To an outside observer that they zoom past, however, they are travelling slower than the speed of light. This works because time passes differently for the observer vs people on the ship. This much I understand, and please correct me if I'm wrong.
But what does this mean for the people in the ship observing objects that they are going past? Wouldn't the stars they are passing appear to be going faster than the speed of light relative to them (because time has slowed down for them)? But if everything is relative, and there's no absolute frame of reference common to everything (like the Aether theory), how can this be possible? As far as they're concerned, they are observing objects moving faster than the speed of light, which is meant to be impossible. Isn't this a paradox?
Or is it a case of if the faster than light objects are all moving in the same direction relative to you then you can conclude that it must be you who is moving at a relativistic speed. But even that still requires some sort of absolute frame of reference. I though relativity solved this problem, but the more I think about it, it actually doesn't. What am I missing?
In physics, to consider something's perspective is to see through its reference frame where it's stationary, but relativity postulates light is always moving at c in all reference frames. So the question of light's perspective is nonsensical.
At school we had triple period English poetry - time DEFINTELY slowed down during this time. The same with stats @ uni!
LOL
For me, that would have increased the speed of time.
@@ankavoskuilen1725 For clarification, it was learning about poetry not writing it, though that probably would have been tortuous for me too... and I was a teenager at the time. Hopefully poetry class is very different today. I have since developed an interest in etymology, but sadly still lacking an interest in poetry (I do appreciate song lyrics as a form of poetry though - it's a pity my English teacher didn't point that out to the class at the time...)
I know your comment was humour, but in all seriousness have you noticed your perception of time changing? I can actually remember how long a second was when I was at primary school. I can tap a finger to the ticking of the clock, and it's slower than what it is today. A second when I was 10 actually lasted longer than a present day second.
@@BrandyBalloon It could be age related... time just seems to fky now I renember school terms seeming to last forever...
Question: If I particle of light has a location uncertainty that spreads over time, could a later measurement of position at x2 it be observed to have travelled further along than the speed of light should have allowed? Or
- Are the distances + precision required too small to be experimented currently?
- Does the spread of positional uncertainty have a hard cap beyond the distance that the speed of light should allow the particle to travel?
- Does knowing the necessary detail of the initial position of light mean that any experiment is necessarily too difficult (eg the resulting frequency uncertainty being so large)?
Brilliant explanation. Tyvm.
I'm so glad that you took the time to make this video Sabine! 👍👍
The Concept of Time, which we created, came from our observation of change, therefore "change is time" as in "things moving, decaying, growing and so on indicate a difference between its present status and its past ones, and with enough data a prediction of future statuses may be doable".
Since Time is not some kinda magic, but just change, we can say that time is just our reconstruction of the past with given present data, in the evermarching present, and possible predictions of the future.
Time may be standardized in different situations, where it may flow faster or slower, by using a standard to measure it (nuclear clocks are the best) and that ACTUALLY DOES NOT create any problem because "if the more gravity there is, the slower time flows, then one place just has time flowing slower".
More than this can not be said, because things like WHY the speed of light is what it is, and so on, is not yet known.
Ngl this kinda sounds like mushroom talk
@@PlatypusMusiq It isn't.
Entropy + momentum
"The Concept of Time, which we created, came from our observation of change, therefore "change is time""
You're on the right way.
If you choose to be cryogenic, you will age/change slower. But does this mean that cryonics slows down time ?
@@noname8192 Not in the magical sense, yes in the physical and chemical sense.
It takes about 8 minutes for the Sun's light to reach earth & the longer light exists, the more stretched out it gets (red shifted.) Light also bends around due to gravitational lensing. Gravity, from my understanding, is just the modification of time around mass.
If we could properly find a proper way to to go light speed, would time stop? No, it would just slow down to the point everything would look like it stopped moving.
The question I have is: you could go FTL, could you see anything. We see things based off partials bouncing off objects then into our eyes, if we could achieve FTL could our eyes interact with light or would we be blind.
When we move from one point to another in Euclidean space, we have a different perspective to the world around us from every point in space. In spacetime, we have a different perspective to the world around us from every different speed. But due to the hyperbolic “metric” it works not 100% analogues to the perspectives in Euclidean spaces. In Euclidean spaces, the angle under which we see an object is the same on some circular arc over a certain chord of a circle due to the circumference angle Theorem. In spacetime, instead of chords of a circle you have to deal with chords of a certain hyperbolas. In Euclidean space, a “zero-way” (path of length 0) ist just a single point, in spacetime it is (with c=1) just a track under 45 degrees (including the single points).
With respect to the “viewing angle”, an object in Euclidean space appears bigger, so closer you get to it. In Spacetime (with a respective definition of “viewing angle”) the opposite is true. The “viewing angle” under which you see an object is as smaller, as faster it is moving relative to the inertial system of you as the observer.
The Garage Paradoxon of SRT is nearly the same in both cases. If you turn a pole of the length of 2 meters into a position, from when you can see it under a view of 60 degrees or more, it easily fits through a door of 1m width, just as a moving pole of 8 meters length fits in you 6 meter garage, if you only move it (the pole, of course) fast enough. With the Twin Paradoxon it is not just as easy, as you have to integrate along respective paths. At least, I do not have an analogy.
The distance from Frankfurt to Munich is 430 km, only if you stay in one place but don’t drive it. On the other hand, You can do both ways by driving you car for 200 km only, if you only drive fast enough. And if your car would need a certain amount of kWh per km only, you could even save energy by excessive sprinting (friction neglected). And, of course, back in Frankfurt, you are younger than your friend, who stayed there waiting for you.
If I understand the formulas of SRT right, they do not allow for travelling faster than the speed of light. If you could exceed the speed of light, the orientation of spacetime would change and time would start running backwards. But there is the barrier of an infinite amount of energy needed. Anyway, this formulas don’t tell you anything about possibilities of compressing or expanding space itself. Nevertheless, the equations of ART allow for an expanding universe or the existence or creating of wormholes. But this is not about travelling faster than light at all. It is nothing but a theoretical possibility to find or create shorter paths in spacetime. Which would give a new quality to the question of simultaneity: If you would hitchhike from Andromeda to earth, it is just a matter of which rout your driver will take. If he goes to the left, you will arrive in Ancient Rome, if he goes to the right, you will arrive in America together with the Mayflower. But if you use the latest warp-drive, you will be here in 42 years from now. At latest. And all at the same time. Make your choice!
Do you find anything interesting in the idea’s of physicists, like Julian Barbour and some others, who claim that time is an illusion? (Maybe an illusion caused by entropy, I guess)
Yes, I find it interesting. But whether time is an illusion or not, it sure is very useful to order events that we observe.
Please do an episode on Julian Barbour
@@SabineHossenfelder well, it kinda stops everything from happening all at once!
@@andywason3414
That's not what I observe at work. Fan spins and everything hits it at once.
In a sense time is an illusion of the human mind and the senses.
The question that comes to my mind thinking about time stopping at the speed of light is: How does light have a frequency if it can't experience time?
A photon doesn't have a frequency, that is, not intrinsically. Rather, we assign a photon a number we call frequency. This should be perfectly sensible given that the number we assign to a photon frequency is observer dependent.
@@kylelochlann5053 Frequency (wavelength) has to do with probabilities of interactions at certain places and times, photon is point particle though in modern QED
@@RWZiggy So, how exactly is a photon a point particle if there's no photon position operator?
@@kylelochlann5053 You can look it up, it can be and has been constructed. All elementary particles are point particles, anything "wavelike" about them are only probabilities
@@RWZiggy What do you mean "look it up" I have a graduate degree in physics. You're not making any sense. There is no such thing as a position operator for a photon, or any massless particle, for "point-like" to make any sense.
When the graph suggests to be the cone shape of an observer registering the world through, the diagonal at 45° would be the shortest route for light reaching his eyes.
The diagonals at each side (not space and time, but the event horizon) predict it will take longer before the light reaches his eyes there.
The constant cannot prevent there is a difference in spatial distance between the sources.
So, at the sides events are delayed. Seen slightly later than they happened.
Nearer by time (events) goes faster for the observer/ further away time is slowed down. One does not observe the real speed of the moon for instance.
Because of the distance equivalent. Something like Newton's law of gravity.
So, outside the cone for the observer the world probability distribution does not even exist.
There is a spacetime dimension involved in the event string fabric, which needs to be the same constant in order to be observable. Also because eyes use a typical wavelength of light for recognition. Anything outside the spectrum is not registered.
But also anything outside the event horizon probability dimension is not registered.
I can’t wrap my head around this at all but when I read “River Of Time” by Novikov there were times that i could grasp bits and pieces.
6:06 We also measure gravitational waves to move at the local vacuum speed of light.
Perhaps it should be the other way around in that the maximum speed is the local speed of low amplitude gravitational waves, and that perturbations of the electromagnetic field also propagate at this local vacuum speed.
I'm not sure the word "local" means anything in this context.
As I understand it ALL zero-rest-mass particles. Google says also gluons.
@@W1ngSMC local means within experimentally measurable reach
@@transientaardvark6231 Gluons don't have asymptotic states so they're sometimes not thought of as physical particles in the way, say, an electron is particle but rather are thought of calculation devices.
Yes, for all massless particles we have a spacetime distance of zero.
@@W1ngSMC "Local" is necessary as there's no such thing as a global inertial reference frame.
My kids and I were discussing this the other day. Referenced them to you for clarity!!
Thanks, it's a nice introduction. Two aspects I would have liked to learn more about:
* Can there still be something like an arrow of causality from the perspective of the photon, such as the creation of the photon is the causally before its absorption? (Even if the proper time distance between those events is zero). What kind of foundation for causality could justify this?
* Roger Penrose talks a lot about how a universe with only photons has conformal symmetry, which if I understand correctly means that distance and time are meaningless, but angles might still have meaning as well as (?) causality. What are your thoughts about this? Like, is it an indication that distance and time are less fundamental than other aspects of reality?
I have always thought of the speed of light as in a certain sense infinite. If you think about it, from the perspective of a lone observer, there is no speed limit. If you made a journey at 90% the speed of light, and on the way back put twice the energy into the acceleration, the journey would take half the time as you expect, it is just that the time it has taken for you and the time it has taken for others is not the same. With this, it makes total sense for the speed of light to be unreachable. You would need to accelerate enough to reach your destination instantaneously (again, from your perspective), in other words infinite velocity which would require infinite energy.
That's how I think of it. 👍
Could you make video on What is time? Why is it? And current research too
Time is what keeps everything from happening all at once.
Except for photons, apparently.
@@MichaelPizyea but sadly is has been (sort of) proven to be equivalent to the law of entropy which basically means time is only an illusion because it means that putting back the atoms of a broken glass is the same as reversing time. It’s sad cause I love clocks and many feel similar.
@@howmathematicianscreatemat9226 Clocks iz kewl. I've never been much into them but I admire their precision, especially watches with such tiny mechanisms. I find mechanical clocks more interesting than electronic or atomic for that reason.
As for what time is, I was being tongue-in-cheek with the old saw about everything happening at once. Except for photons, apparently. 😁
Time is what particles that exhibit mass experience, like us and our everyday experience.
Because we're made of particles that exhibit mass, we're the weird ones as we experience life 'slowed down' from the speed of causality's 'instantaneous' experience. Since light isn't known to interact with the Higgs mechanism and therefore exhibit mass, it is believed to be massless and therefore light and other 'massless' particles experience time instantaneously.
Time is motion. They are the same thing. We define time by the motion of a timekeeping device. Your perception of time is determined by the motion of particles in your brain. As to why? No idea.
I thought in Relativity the concept of light's "perspective" makes no sense? Mathematically you're literally dividing by 0 which is also another concept that makes no sense either.
Yes, I thought the whole thing was that light has no proper time at all, and that it has no reference frame.
@@erinm9445 proper time is fine (and zero), but indeed it has no valid frame of reference
If you imagine that a particle can either move or interact, its speed becomes quantity of movement/quantity of interaction.
In the case of light, the amount of interaction is zero, which effectively means dividing by 0 if we want to calculate its speed. And even if we don't know how to divide by 0 mathematically, the physical meaning of this equation is obvious enough to know that quantity of movement/0 = quantity of movement.
When light is reflected what happens to the speed of light. The part that always gets me is the definition is precise...THE SPEED OF LIGHT IN A VACUUM IS THE DEFINED SPEED OF LIGHT. Where exactly in the universe is there a vacuum. I know many parts of space are in a near vacuum but I doubt any part of space is in a complete vacuum. (Here I have to imagine a region of space at absolute 0 where the matter have no energy to move, otherwise that region of space might have no matter now but that is not true in the past or in the future as the matter has energy and movement surrounding it) If there is no vacuum, meaning some matter is in the vicinity, than the speed of the photon does not equal this definition; which means light or the photon does experience time even though that number is very very tiny.
the photon is at c in any medium, the premise "light is slower" in a medium is simply wrong
@@neutronium_goes_wild I will not say you are wrong and I have heard that for instance light through water does not change the speed as it is a distance times time equation as the light covers more space in water. But your overall theory does not jive with the official definition concerning vacuum and the speed of light
Lovely. Enjoyed. Appreciate
Please talk about how your working day now differs from when you were working in academia. What are your fears regarding success? How do you stay motivated? How long do you expect it to last?
Please ignore this guy. Most of us are more interested in science than in your private affairs.
Truly timeless and glowing
for verticals (ksp travellers; german): eine interpretation auf die schnelle ist, dass licht keine persönliche zeit hat, also licht der maßstab ist, an dem man genau die koordinierte zeit misst, und bezogen auf KSP wäre also zunächst mal wichtig festzuhalten, dass ein target, nehmen wir einfach mal tylo, in der koordinierten raumzeit zeitlich gesehen immer an fast der selben stelle ist. wenn man seine aufenthaltsbereiche im griff hat, wird die persönliche zeit (in ihrer abhängigkeit von der "schnellsten", koordinierten (also unpersönlichen lichtzeit, die wohl mit kaum 3 wimpernschlägen bemessen sein sollte) egal in welchem raum der grade steht immer fast (oder annähernd) die gleiche sein. mal schneller, wenn er räimlich günstig steht, mal grade soviel länger, wie das raumschiff persönlich braucht, um den hier verschiedenen raum zu überbrücken. --> sprich der schnellste weg zu tylo wird nicht von uns persönlich zurückgelegt, sondern von licht, mit dem man sich aber zumindest koordinieren kann, und dann hat tylo nur noch die koordinaten von Zoooom & zyyyyyym, also ist sehr nah, mit tiny tiny unterschieden. naja... soviel mal dazu
erklärt zb die ulkigen blob atosekunden freezebilder, die man manchmal noch zerflikkert sieht, wenn man in eine SOI eintrifft. vielleicht ist das ein hinweis darauf, das man gerade persönlich neben dem koordinierten licht dort angekommen ist. das licht hat sich einfach mal zyym dahin gezoomt und wir mit unsre persönliche zeit och; nu simma all da
From Wikipedia: Proper time can only be defined for timelike paths through spacetime which allow for the construction of an accompanying set of physical rulers and clocks. The same formalism for spacelike paths leads to a measurement of proper distance rather than proper time. For lightlike paths, there exists no concept of proper time and it is undefined as the spacetime interval is zero
Can you please do an episode where you describe how you designed your brilliant courses and why? I think that would be really interesting and get more attention than the advertisement blurbs at the end!
I’ve read light travels from the sun in a certain amount of time. But are you saying it is zero time?
It takes 8 minutes in our coordinate time. It takes no time for the light itself.
@@SabineHossenfelder I always thought the story about how cosmic ray muons reach the earth's surface even though the earth's atmosphere is too thick is a great example of space-time dilation and length contraction on things travelling that fast.
@@SabineHossenfelder except any experimentalist who's built a Cherenkov detector knows n = (1+eta) for a gas, and v=c/n so gamma = 1/sqrt(2eta) --> 43 for air. It has a little time at the end.
We see light take 8 minutes, but if you were traveling at the speed of light from the sun to the earth, you would "teleport" - it would appear instantaneous, no time would pass.
@@SabineHossenfelderYES! The propagation of "light" is simply the transfer of information, the photons themselves may as well be stationary....
Hi Sabine, thx for the great video as always! Could you make a video about the “time” before the electroweak symmetry breaking? I thought we believe that all known particles were massless then, so how do we picture time then?
Thanks for the answer, Was always confused when I heard that the light from the sun takes around 8 Minutes, but time also doesn't pass for it.
Dear [Video Creator],
I am writing to request a video that showcases the strange and fascinating warping geometry of black holes. As you may know, black holes are among the most mysterious and intriguing objects in the universe, with properties that challenge our understanding of physics and the nature of reality.
One of the most striking features of black holes is their ability to warp space-time, creating a gravitational lensing effect that bends light around them. This effect can cause the light from distant objects to appear warped or stretched, creating the illusion of a ring of light around the black hole.
I would love to see a video that visualizes this warping geometry in a clear and engaging way, using the latest simulations and animations to bring the concept to life. The video could explore the physics behind black holes and their warping of space-time, as well as the implications of this phenomenon for our understanding of the universe.
I believe that a video on this topic would be a valuable resource for anyone interested in physics, astronomy, or the mysteries of the universe. Thank you for your consideration, and I look forward to seeing the final product.
I have no one who could do such a simulation, sorry
I just chatgpt a TH-cam comment?
What a blatant and obvious ChatGPT copy-paste. You could've just typed what you wanted to see on the channel yourself instead of this, but hey you do you I guess.
@@yndihalda I will!
Just watch Interstellar, not quite what you asked for but still a good approximation of the physics.
@SabineHossenfelder Thats why the photographs don't move! The photons stopped the time, the moment they hit the emulsion of the film!
Thank you Sabine you made me see, the Einsteinian mind!
@SabineHossenfelder Deshalb bewegen sich die Fotos nicht! Die Photonen haben die Zeit angehalten, als sie auf die Emulsion des Films trafen!
Danke, Sabine, du hast mir den Einsteinschen Verstand gezeigt!🌈
It's not an insight that time must be a coordinate that has to be joined with three dimensions of space, it's a lack of insight. The field equations require four arbitrary number lines. The lack of insight is that only from an observers point of view looking through a pair of eyes, stereoscopically speaking, would you describe a space with three dimensions and therefore be one dimension short and need a stand in like time to market the concept to the wider audience and be nominated for a Nobel prize.
The space around any finite point of matter can be readily described in terms of four dimensions, a square area is the line squared, the line has one dimension, the square has two dimensions, now square the square so that you have two intersecting planes at ninety degrees perpendicular to each other with a central axis and you have your four required dimensions - the four arbitrary number lines which is a coordinate system capable of defining space from a point to infinity in all directions. No time required. Einstein was right when he said he was no Einstein! Now that's settled we can restore time to it's proper place as a reciprocal of energy. Enough of the garbage physics.
It's worth noting that clocks do not measure time. Clocks measure all sorts of things depending how they operate, but they do NOT measure time. Generally, they measure vibrations of some sort. And as velocity increases, so does the mass of every accelerated particle. And because Conservation of Momentum exists, as particles gain mass, the rate at which they vibrate reduces.
But it is wrong to say that time is slowing down. It isn't. It's ticking at the same rate as always. There is an APPARENT dilation of time, due to increased mass, but the rate time passes does not change. It is the rate at which things happen which slows down. And this is a subtle but important point.
Einstein did us a great disservice by equating clocks with time. The two things are not the same.
And this properly explains the so-called Twins Paradox, too. There is no missing time! It's simply that the person's particles travelling in space have slowed their vibration rate as a result of their increased mass. This effect works to give an apparent time dilation, while time keeps passing as per normal. It's just that fewer things happen in the same amount of time.
And we KNOW this is correct, because if time actually slowed down, then we would observe some sort of unexplained "double slowdown".
Unfortunately the last time I checked Light was busy using the Death Note to rid the world of criminals he thinks deserved to die.
👀
Light here. I have seen every future you have made, and every history yet to unfold. And in them all, there is a very good reason no one in the galaxy talks to you.
I find this really interesting. I think a common pitfall is to think that the passing of proper time is similar to the way we experience time, but for a photon there is no consciousness or brain that does the experiencing. This makes it hard to get an intuitive idea of the concept.
I would find it interesting if you could make a video on the science leading up to special relativity. From Galilei and Newton to Maxwell to Lorentz and Poincaré.
time is for all observers the very same
Thank you for this video! I was wondering if you had any resources that explain why the Lorentzian distance is "right" for spacetime rather than some other distance? I don't have much of a physics background, but I did recently finish my Ph.D. in mathematics (focusing on Universal Algebra, specifically natural dualities), so I'd be happy with any math-heavy explanation. Thanks again for the video and have a nice day!
I always saw the distance done the other way around: space interval minus time interval. Then you can write the coordinates of an event as (x, y, z, ict) and apply the normal Pythagorean distance formula, which is easy to remember.
Glad it’s all being sorted out now , it’s being on my mind for years
Sabine, imo Your channel is among the best science channels on YT. But I think You can be mistaken this time. Einsteins' postulates, 1.the laws of physics are the same for all inertial frames 2.the speed of light in vaccum is constant in ALL intertial frames. So light DOES NOT have an inertial frame - we can't look from perspective where light is at rest, because that validates the second postulate - light's never at rest it is ALLWAYS 'c'. So the whole concept is meaningless. You can't use Einsteins' special relativity while validating one of postulates He built it upon :)
Photon#1: Where will you be?
Photon#2: I'll be where I'm at! Instantly!
It is mind-blasting to realize that a photon emitting from the surface of the sun, and a photon emitting from a star in Andromeda galaxy, takes the same time to reach Earth, which from both photons' perspective', is 0.
We all know that Sabine gives the most concise and most simple explanations to scientific theories. She can make the most mundane understand the complex at least in principal. So the only thing I can say on this video is that it must be so complex even Sabine can’t get me to follow it 😂🤦♂️
Interesting discussion. It should be for light three time dimensions. First, - light is magnetic wave with frequency f that should follow vibrations by time otherwise will be messed. Second is light or magnetic vibration photon with speed carrying energy E = hv and if time 0 energy goes to infinity? Third there is observer Sabina with Einstein telling that during 1 second photon made 300000 km. So coming question do time can disappear for light ?
The speed of light is always fascinating to think about. Question: Why are gravitational waves moving at this speed?
Is it because the graviton is massless? (As I have been told, everything massless MUST move at the speed of light).
I’m not sure if this is accurate but this the intuition I’ve arrived upon. Imagine that you are a being with zero capacity for internal change. Unless something from the outside acts upon you, you don’t change, full stop. Being internally changeless, any minuscule change in your environment seems like infinite change to you. Things zoom by you at break neck speed.
But from your environment’s perspective, it’s you that’s zooming by. And on a mysterious and seemingly unrelated note, you experience zero time. The environment calls you a photon.
In reality, those two properties of a photon are directly related. A thing with zero internal change directly entails traveling at astronomical speeds relative to anything else that does have the potential for internal change. And that’s why a photon’s speed is the maximum speed limit, because you can’t go any lower than zero internal change.
It's still somewhat paradoxical, because then according to a photon, it doesn't exist. The moment it was emitted is exactly the same moment it was absorbed, no matter how far it traveled. So there's no time in which it actually existed...
This kind of paradox usually arises from making questionable assumptions at the start. The problem with this one is the notion of a photon being able to experience time at all. It does't "experience" anything. Anything complex enough to be have any kind of awareness cannot achieve light speed. Problem solved 🙂
@@BrandyBalloon Nothing to do with awareness... Experience is in another meaning here. A neutrino can experience transition to another kind of neutrino, and electron can experience interactions and collisions...
if light travels at 45 degrees and anything higher is FTL then by bending space time using warp drives is more plausable then simply boosting an engine up to the speed of light to quote prot from kpax movie "now if you dont mind i have a beam of light to catch"
As a former Physics major, my interest in quantum mechanics started with relativity of time and ended when more than 3 freek letters were introduced in the equation I honestly wondered if it would make things easier if I knew greek alphabets because my brain just froze trying to distinguish one squiggly letter from another. It did not help that my professor had a hand writing that was only slightly better than chicken scratch 😂😂
I love how you explain things
I absolutely loved it.
I also have a question.
Can you explain why the graviton is not part of the standard model exept for the fact that we don't measure it?
(I'm hinting at the renormalization problem)
Cause they decided there is no graviton, space is sheety, like a sheet.
This begs the question: then a photon is everywhere within its path at the same time, like a long 1-dimensional object instead of a point-like particle? Very confusing...
These days I was reflecting on how similar the spatial and temporal dimensions were, and if they are really identifiable. I do not have any diploma in physics, I am an engineer and I have self-taught relativity. As I understand it, in relativity, the concept of space-time is presented, although I do not know the theory well enough to confirm whether both dimensions are treated identically. For example, in relativity, something as simple as the concept of speed, traveling a certain distance (in one dimension) in a certain time, is identifiable with traveling a distance in two dimensions? I would love to know for sure if this is true or not, and why this is so. Thank you Sabine for your videos, and I hope this comment reaches you.
Great video, it would be great if you do a video on the science behind the move Interstellar
One interesting way to think about it is that we, our body, is made up of matter. Matter that is held together by interactions and forces mediated by photons, gluons, things that are light and move at the speed of light. Those interactions are the tick of our internal clock. As we move faster and faster though space those interactions happen over longer and longer distances, but for us one second is always one second. For the more stationary observer their one second is different than our internal clock. As we travel closer and closer to the speed of causality, it takes longer and longer time for those interactions that make matter, eventually those interactions stop because the light can never get to the next interaction. And if interactions stop our clocks stop ... and time is no longer a thing.
I know what this means. It means that a photon is a mini wormhole-- it tunnels through time and draws together two points in space. It's not communicating BETWEEN them, it's literally folding them onto each other.