To make it a bit more graspable; A baseball at 90% the speed of light will cause a fairly large nuclear detonation. [0]
This particle moved at 99.99999999999999999999951% the speed of light. IIRC from when I worked it out a month ago or so (baseball with that speed), it was in the region of 10^25 J, pretty close the energy the entire sun is outputting each second or a couple million nuclear bombs. (10^25 particles, 4.8 joule per particle)
If such a baseball would interact with your brain, then yes. That would be kill.
If only the particle interacted: no. It's too fast to reasonably interact with something as short as going through a human body with any meaningful amount of energy.
The detector used doesn't interact directly with the particle - it observes the light emitted as the particle (& the subsequent shower) interacts with the atmosphere.
To nitpick: this is only mostly correct. The predominant detection method is actually having arrays of particle detectors on the ground that register through going particles. Because you have an array of them, you can use detection timings of a number of triggered detectors to compute arrival detection/etc.
These more "indirect" detectors get a 10x data collection advantage over fluorescence telescopes because they run 24x7 whereas the telescopes run in clear, moonless nights. (The moon in the field of view can actually burn out the camera.)
Source: subject of my thesis was trying to calibrate the energy measurement of the fluorescence telescopes by using models of the air shower profile and relative light yield from fluorescence vs Cherenkov effects to infer a scalar fluorescence light yield parameter.
HiRes utilized the atmospheric fluorescence technique that was pioneered by the Utah group first in tests at the Volcano Ranch experiment and then with the original Fly's Eye experiment. [0]
The cosmic ray hits a molecule in Earth's atmosphere, which causes it to ionize. When it regains electrons, they emit UV light, and the detector catches this while scanning the sky. [1]
Not on this particle but relevant if you're interested in cosmic particles: For my son's 5th grade Science Fair project we are building a cloud chamber to detect cosmic particles! As crazy as that sounds we've decided on this project after watching videos showing how ridiculously easy it is to build one, e.g. see this one: https://www.youtube.com/watch?v=pewTySxfTQk. Most designs call for dry ice (cheap, ~$10 for 10 lbs but may be hard to find a local store) but you can also build one using an air duster: https://www.youtube.com/watch?v=QCAVlMTBMe0!
Fun fact that I've learned from him during research: humans are exposed to cosmic radiation which is on average equivalent to 10 chest x-rays per year. It would be interesting to look at the impact of this on, e.g. cancer rates among people living at sea level versus cities with high elevation, e.g. Quito in Ecuador.
It would be interesting to look at the impact of this on, e.g. cancer rates among people living at sea level versus cities with high elevation, e.g. Quito in Ecuador.
It is interesting, and there are some studies exploring this and related issues. The results are not always immediately intuitive!
I frequently go to Quito and the radiation you get from the sun at midday (bang on the equator, thin atmosphere) feels equivalent to about 10 chest x-rays per second.
Fun trivia: cloud chambers were invented by a Scot to investigate the formation of clouds while he was based on top of Ben Nevis (the UK's highest and possibly most cloud covered) mountain.
I will remember this fact to cheer myself up next time I am on a misty Scottish mountain top!
Volume/time - pour slowly into a funnel and it works, pour too fast the funnel overflows and you get cancer. People accustomed to high altitudes likely have bigger funnels.
What isn’t known about the relationship between exposure regimes and poor outcomes could fill the complete OED. Is it really a hormesis model? Linear No Threshold? Linear? Supra-linear? Linear-quadratic?
We don’t know, and generally speaking it would be unethical to try and find out using humans.
Fun!! You should consider getting a small sample of an alpha emitter; the tracks of the little helium nuclei are very striking. Your son is a lucky young man.
It just occurred to me there is a relationship between children’s science fairs and the crisis of novel positive results publishing in science.
It always bothered me that science fair projects were “fake science”... nothing new was observed so it wasn’t science at all.
It turns out I was very wrong, and journals that only publish novel positive results and institutions that only reward them are committing a grave scientific error.
If journals start publishing confirmations of previously reported experiments, then students who confirm long reported results will be doing very real science.
Journals could even publish brief (two sentence) articles from students on a back page. I think it would do a lot of good.
this particle physics is just silly and it will never lead to anything but more tiny and faster particles which do inexplicable things. such useful science ... really...
Without being an expert on the subject, I hope some of what is learned from the engineering of those big honking machines might be relevant for attempts at sustainable fusion.
someone correct me if I'm mistaken, but for the particle the time goes so fast that it sees the 215,000 years that we see the photon take to gain a 1 centimeter lead go by in a flash
Yeah, basically. If you were to hitch a ride on this particle, those 215,000 years would go in a flash (basically, how much time it takes light to travel a centimeter). Wherever your final destination was, you would have aged a few fractions of a second but you just traveled nearly 215,000 light years.
Me neither, but I always had the idea, that it is impossible to think about events, at a velocity of c, since it is impossible to properly think about 2 events, that are infinitely separated in time.
The Lorenz-Factor(γ) for a velovity approaching c approaches infinity. Thus, from the reference frame of a particle at c, the time dialation: ΔT = γ*Δt, also becomes infinite. 2 ticks on a clock (Δt) of an ordinary observer, take an infinite amout of time in the reference frame (ΔT).
This doesn't prove or explain anything, but the fact that we can't handle infinities very well, in our casual thinking.
No no no, what we can't handle is objectivity! Everything is relative so it is striking me as absolutely paradox to pretend we could leave our frame of reference anyway and "ride a photon" measuring it's speed with a stop watch.
Instead you simply have to deal with towers of abstractions, understand the experiments. It is counter-intuitive to claim we also couldn't see photons, but really, the disconnect between theory and phenomenology is rather large. I guess we are only really interested in the weak-electromagnetic force. And that's a probabilistic theory thanks to quantum mechanics. Discrete systems are macroscopic simplifications for didactic and deductive reasons.
Gravity is next to the other three basic forces. That's a simple dualism. So time stands still for the photon, but space bends. And we can't fully explain how.
And don't get me started on infinity. It's just a number big enough for all intents and purposes. Conversely, it's pretty simple to think about the opposite: Nothing. So if you you take an infinite amount of time to observe a clock at light speed from your inertial frame of reference, it will just not move at all -- there are no "2 ticks". Corollary: A photon doesn't experience time at all. And this holds in quantum mechanics, because a photon doesn't exist until observed. A photon is thus the measure of interaction, a delta on our clock. Colloquially, time is the order of events -- if nothing happens, time stands still.
For sake of the argument: If you just switch the photon and observer in your example, the photon in infinite time wouldn't "see" any time pass on the outside observers clock. He wouldn't move. But this is just too simplistic, you have two points in space that practically can't move, because they don't
From the frame of reference of a photon, the environment would
> 2 ticks on a clock (ΔT) at c, take an infinite amout of time in the reference frame of an ordinary observer (Δt).
Extending the thought, you are trying to multiply infinity by infinity. As you said, we cannot handle infinities. I guess that is because there can be only one, one singularity, one universe. That's why the speed of light is set at unit-interval.
The speed of light is a result of the laws of electromagnetism. No matter how fast you move the laws of electromagnetism and therefore the speed of light wont change.
I know of no way to make it intuitive though. Things improve slightly if you replace speed with 'rapidity' which places the speed of light at infinity, but then you get that objects with infinite rapidity don't travel instantly from one place to another (although this is true in some frames of reference).
The speed of light is, but it does not have anything to do with relativity.
Those concepts are connected by the speed of light in vacuum, yes, but there is no logical reason for that. This was an educated guess, and was confirmed by observation it's not a conclusion.
Einstein started to formulate special relativity theory starting from an assumption that a "ball of light" won't change its shape for non-inertial (no accelerarion) observers regardless of their respective speed. I.e. constant speed of light was the reason not a result of this theory.
> For some reason I've never been able to wrap my head around this. Anyone know a good explanation for this stuff?
There's no explanation "needed". Light photons move at a constant speed from any viewpoint. Its just a fact that is experimentally confirmed.
Perhaps what you need is an experiment that proves this to be true. But those experiments don't offer you any "explanation", they just will prove what you already have been told.
One thing that helped me understand it all is that "Reality" is a wave that propagates out. We call it "the speed of light", but its far more accurate to call it "The speed of reality" or perhaps "The speed of causality".
Basically, when A causes B, that "event" takes time to propagate to other locations. This means that different observers sees the event happen at different times.
For example: the galaxies 3-billion light years away from us appear to be forming today. We know the information is 3-billion years old, but reality itself is warped. Because the reality from 3-billion years ago was 3-billion light years away, its basically happening right now from our point of view (The "wave of reality" is finally reaching us).
Calling it the "speed of light" is confusing for multiple reasons. Just call it the "speed of reality" (and light in a vacuum happens to travel at this speed) and in my eyes, it becomes way easier to understand.
I don't think they're doubting it's a fact, but rather just saying it's a fact they don't understand. Saying "no one needs to explain the theory of relativity" implies it's intuitive to everyone, which is very obviously not true.
Hand-waving isn't an explanation, it's a distraction.
I think 'dragontamer read the question as "why does the photon move away from it at the speed of light?" (as I did). There isn't really an answer to that question, since it's just the way the universe works.
Saying that the laws of the universe don't (or can't) have explanations is not the same as saying they are intuitive to everyone. Ultimately, some of those facts you just have to accept. It is extremely difficult to have any useful analogy or explanation that attempts to explain why light always travels at the speed of light in any reference frame.
The consequences can definitely be explained well, but the fundamental laws really can't.
EDIT:
John von Neumann's quote about math reflects my view about this kind of fundamental physics:
> in mathematics you don't understand things. You just get used to them.
I'm not trying to say its intuitive. I'm saying that a lot of physics / science describes the consequences of certain facts. A lot of facts don't actually have "deeper explanations".
As another poster described: Why do Magnets attract each other, but sometimes repel each other?
Well, we can list a ton of consequences, make up stories about negative charge and positive charge (but then why do THOSE things attract / repel each other??). We can craft mathematical laws that describes the nature of this attraction.
But at the end of the day, its just a fact you have to accept. Reality has these things called magnets: they're made up of things that attract each other.
Similarly: Reality itself moves at a certain speed. Physicists call that speed "The Speed of Light". From everyone's point of view, reality propagates out like a wave, and space itself warps to keep things consistent. Its weird. But that's just how the world works.
Step 1 is accepting the fact. Step 2 is performing calculations so that we can start taking advantage of those relativistic effects in engineering and design.
Time stands still for the photon and is super slow for the particle. Super slow is still infinitely away from 0. In the article example from the particles view, 0.000..1 seconds pass for the photon to be 1cm ahead being the photon is so fast. From our view however that same small time is dilated to the 200k years.
This is all true.... However it should be said that time is not super slow for the particle, from the particles point of view (frame of reference) time passes as per normal for itself.
This is what allows the photon to appear to continue to travel at the speed of light from the particles frame of reference.
If the particle was carrying a clock, and we could watch it tick as it flew away from us, it would appear to be ticking super slowly, the second hand would take forever to move.
Conversely if we had a giant clock and the particle could watch it as it flew away from us, it would appear to be ticking super fast, it would look as though we were travelling far into the future.
The same is also true if an object is close to a very large gravity well. If someone could stand next to the event horizon of a black hole and hold a giant clock, from our point of view, their clock would appear to tick very slowly. From their point of view, it would tick normally, but our clock would rapidly tick far into the future. The universe around them would quickly travel into the future.
Time and space are elastic to allow the speed of light to remain constant.
There's something I don't understand about that type of explanation.
Say a particle and I are moving along like so:
-----[photon @ speed of light]-->
-----[me @ 50% speed of light]-->
Or more simplified, say two cars are moving like so:
-----[other car]-->
-----[my car]-->
When I'm stationary, I see him go past at 100km/h. When I move at 50km/h, in the real world he would now appear to only be going 50km/h. But if I slow down my time to half speed, now he'll look like he's going 100km/h again. Because he looks to me like he's at 50km/h at double time speed = 100km/h. That seems to make sense - time slows down and the apparent speed stays at C (100km/h in this case).
That's how I've understood the explanation for relativity. But it must be a very wrong understanding - because that whole idea breaks down when the other car is going along a different vector to me! In this situation:
<----[other car @ 100km/h]--
-----[my car @ 50km/h]-->
His speed relative to me would come out as 150km/h in the real world, and no amount of making him look like he's going faster would reduce his speed to 100km/h.
Your measurement of time and space will always adjust to ensure light travels at a constant speed.
Time dilates, length contracts. So perhaps it would "look" like the car travelled a smaller distance over a longer period of time that what you expected, from your frame of reference, versus a third observer who can see you both.
Thanks, that looks like what I'm talking about and I'll have a read through. It looks like pretty dense reading but the equations mostly don't look too horrible.
> Your measurement of time and space will always adjust to ensure light travels at a constant speed.
Enough with the metaphors already, the measurements don't do anything, you, or rather phyisicists and the like do measurements, and they adjust numbers normalized to c=1 because how else would you do it. There is no way to synchronize clocks because of the CAP theorem, nevermind relativity.
Imagine you were driving a car with a stuck accelerator an no brakes. The car always moves at 100 MPH. So you can't change the car's speed, but you can change its direction. So you can drive north, at which point your east-west velocity is zero, or you can drive east, at which point your north-south velocity is zero, or you can drive in some other direction, which will give you a mix of north-south and east-west velocities. The faster you move east-west, the slower you move north-south and vice versa.
You are kind of like that car. You (and everything else) are always moving at the speed of light, but through spaceTIME, not through space. When you move through space you are not changing your speed through spacetime, you are only changing your direction. The faster you move through space, the slower you move through time, and vice versa.
This is fascinating to think about, and easy to understand. Thanks. I'd like to read a book on this subject written a similar manner. I remember trying to read The Fabric of the Cosmos as a leisure reading book (I like nonfiction) but it got super tedious halfway through and I had to put it down.
The bug in your explanation is that turning the steering wheel performs a rotation (which moves vectors along the edges of circles) on your velocity vector, but in spacetime that would be a hyperbolic rotation (which moves vectors along hyperbolas). The result of this is:
If I am an outside observer measuring your position with a very long ruler and your time with my wristwatch, all while watching your dashboard clock, I have access to three numbers. (Your clock, my watch, your position on my long ruler.)
There are three ways to compare these numbers. If I compare my watch to your position down the ruler, I will obtain "classical speed." The behavior of this number is very confusing when it is high.
I may also compare your dashboard clock with my ruler position, or your dashboard clock with my watch. Both of these can lead to a "speed," in the sense of one number changing at a certian rate with respect to another.
If Vx is the rate of change of the ruler position with respect to your dashboard clock, and Vt is the rate of change of my wristwatch with respect to your dashboard clock, and c is the speed of light, then it turns out to be always true that c^2*Vt^2 - Vx^2 = c^2. If you graph this you will see that it is a hyperbola.
In the parent's example, the car situation would obey V(north)^2 + V(south)^2 = 100mph^2. If you graph that it is a circle, as it differs from the above by the minus sign.
Yes, I know that, but I think this inaccuracy is a price worth paying to achieve an initial intuitive understanding. As a student reflects more deeply on what it can possibly mean to "move more slowly through time" the negative sign on the time dimension can be introduced. But as an initial intuitive picture to get a student out the the Galilean rut I think the circular rotation works well.
That part is actually harder for me to understand. The photon experiences no passage of time, right? And yet it does move through space. Or would you say that, from the reference point of a photo, there is no movement in time or space?
Or perhaps it’s better to just say that the concept of reference points hits an asymptote at velocity c, so it simply doesn’t make sense to talk about the reference frame of a photon.
Can photons interact? If they can, what happens when you have two photons cancelling each other out at different distances from their origin? From the photon reference frame, both were emitted and absorbed at T=0, but in our reference frames they were emitted at different times.
Does that somehow link the emission time of the two given that there is a reference frame in which they are equivalent?
* The flux of particles in this energy regime is so low that you get about 1 per square kilometer per century, so studying them necessitates doing really wild stuff like instrumenting a patch of land the size of Rhode Island.
* These particles are so energetic that in their frame the nominally low-energy photons that comprise the cosmic microwave background appear as an impenetrable gamma ray wall thats prevents them from traveling more than about 100 million lightyears. This seems like an incredible distance but in astronomical terms this means that whatever is producing them is "nearby." We also know they don't come from our own galaxy because arrival directions don't correlate to the galactic plane.
* Current consensus says that these particles probably come from very large and active black holes in the center of certain galaxies. These objects are called active galactic nuclei (AGN).
- Would the CMB be so energetic (from the proton's frame) as to create electron-positron pairs?
- If the particle can't travel more than 100m light-years, what happens to it? Does it slow down? Get destroyed? Is the answer markedly different from our reference frame vs the particle's?
Arg. Had a moderately long, not quite Randall Munroe worthy explanation written up but it got lost by accident. Sorry. :(
In a nutshell, that'll never happen. You'd have to be the unluckiest astronaut to ever live. These particles reach Earth at a rate less than 1 per century per square kilometer. So you'd have to hang out in space for like a hundred million years...
The original particle never reaches the ground. It gets annihilated in a collision some tens of kilometers up in the atmosphere.
If you were hit, I'm not sure the cascade would do significant damage before it exited your body on the other side.
For interested parties, here's the most recent paper on anisotropy, ie how we know the particles are extragalactic: https://arxiv.org/abs/1709.07321
I also worked in this field (Pierre Auger Observatory in the Karlsruhe group) before I "sold out" to join a tech company in late 2010. Might we have met?
Back to cosmic ray anisotropy. There was actually a big paper from the Pierre Auger collaboration in 2007 on anisotropy that made it to the cover of Science. It correlated arrival directions with a I catalog of, IIRC, AGNs. I was in my first year in the group so I didn't make the author list yet. I was quite disappointed at the time. Pretty much from the moment of publication, however, the statistical significance we got from the data started decreasing until it was no longer something we were particularly confident in. The collaboration had to publish a note on that. Ouch. We never worked out why this was happening (if other than horrible luck) before I left.
Before the publication there had been interesting internal discussions about whether to publish. The astronomers typically felt the significance was plenty by astronomy standards and we were trying to do astronomy with particles after all! The particle physicists tended to want to apply the more conservative thresholds that are common in accelerator physics. After all, what was our detector if not a giant calorimeter? :)
78 comments
[ 4.3 ms ] story [ 149 ms ] threadThis particle moved at 99.99999999999999999999951% the speed of light. IIRC from when I worked it out a month ago or so (baseball with that speed), it was in the region of 10^25 J, pretty close the energy the entire sun is outputting each second or a couple million nuclear bombs. (10^25 particles, 4.8 joule per particle)
[0]: https://what-if.xkcd.com/1/
https://www.reddit.com/r/askscience/comments/3o16ut/what_wou...
If only the particle interacted: no. It's too fast to reasonably interact with something as short as going through a human body with any meaningful amount of energy.
These more "indirect" detectors get a 10x data collection advantage over fluorescence telescopes because they run 24x7 whereas the telescopes run in clear, moonless nights. (The moon in the field of view can actually burn out the camera.)
Source: subject of my thesis was trying to calibrate the energy measurement of the fluorescence telescopes by using models of the air shower profile and relative light yield from fluorescence vs Cherenkov effects to infer a scalar fluorescence light yield parameter.
The cosmic ray hits a molecule in Earth's atmosphere, which causes it to ionize. When it regains electrons, they emit UV light, and the detector catches this while scanning the sky. [1]
[0] https://en.wikipedia.org/wiki/High_Resolution_Fly%27s_Eye_Co...
[1] http://www.telescopearray.org/index.php/history/history-of-t...
Fun fact that I've learned from him during research: humans are exposed to cosmic radiation which is on average equivalent to 10 chest x-rays per year. It would be interesting to look at the impact of this on, e.g. cancer rates among people living at sea level versus cities with high elevation, e.g. Quito in Ecuador.
It is interesting, and there are some studies exploring this and related issues. The results are not always immediately intuitive!
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113517/ is one good place to start.
I guess that counts as cosmic radiation.
I will remember this fact to cheer myself up next time I am on a misty Scottish mountain top!
We don’t know, and generally speaking it would be unethical to try and find out using humans.
It always bothered me that science fair projects were “fake science”... nothing new was observed so it wasn’t science at all.
It turns out I was very wrong, and journals that only publish novel positive results and institutions that only reward them are committing a grave scientific error.
If journals start publishing confirmations of previously reported experiments, then students who confirm long reported results will be doing very real science.
Journals could even publish brief (two sentence) articles from students on a back page. I think it would do a lot of good.
Here's something actually interesting >.> but no one care about it.... http://aip.scitation.org/doi/abs/10.1063/1.2423240
Plus: https://en.wikipedia.org/wiki/Particle_physics#Practical_app...
Wikipedia has a section on the practical applications of particle physics: https://en.wikipedia.org/wiki/Particle_physics#Practical_app....
For some reason I've never been able to wrap my head around this. Anyone know a good explanation for this stuff?
When Time Breaks Down | Space Time | PBS Digital Studios
At about 4:30 is when they talk about light speed, but you should watch before then to understand what is going on.
The Lorenz-Factor(γ) for a velovity approaching c approaches infinity. Thus, from the reference frame of a particle at c, the time dialation: ΔT = γ*Δt, also becomes infinite. 2 ticks on a clock (Δt) of an ordinary observer, take an infinite amout of time in the reference frame (ΔT).
This doesn't prove or explain anything, but the fact that we can't handle infinities very well, in our casual thinking.
Instead you simply have to deal with towers of abstractions, understand the experiments. It is counter-intuitive to claim we also couldn't see photons, but really, the disconnect between theory and phenomenology is rather large. I guess we are only really interested in the weak-electromagnetic force. And that's a probabilistic theory thanks to quantum mechanics. Discrete systems are macroscopic simplifications for didactic and deductive reasons.
Gravity is next to the other three basic forces. That's a simple dualism. So time stands still for the photon, but space bends. And we can't fully explain how.
And don't get me started on infinity. It's just a number big enough for all intents and purposes. Conversely, it's pretty simple to think about the opposite: Nothing. So if you you take an infinite amount of time to observe a clock at light speed from your inertial frame of reference, it will just not move at all -- there are no "2 ticks". Corollary: A photon doesn't experience time at all. And this holds in quantum mechanics, because a photon doesn't exist until observed. A photon is thus the measure of interaction, a delta on our clock. Colloquially, time is the order of events -- if nothing happens, time stands still.
For sake of the argument: If you just switch the photon and observer in your example, the photon in infinite time wouldn't "see" any time pass on the outside observers clock. He wouldn't move. But this is just too simplistic, you have two points in space that practically can't move, because they don't
From the frame of reference of a photon, the environment would
> 2 ticks on a clock (ΔT) at c, take an infinite amout of time in the reference frame of an ordinary observer (Δt).
Extending the thought, you are trying to multiply infinity by infinity. As you said, we cannot handle infinities. I guess that is because there can be only one, one singularity, one universe. That's why the speed of light is set at unit-interval.
Sounds like the Matrix.
Sounds like a processor tick.
Sounds like a register.
I know of no way to make it intuitive though. Things improve slightly if you replace speed with 'rapidity' which places the speed of light at infinity, but then you get that objects with infinite rapidity don't travel instantly from one place to another (although this is true in some frames of reference).
Those concepts are connected by the speed of light in vacuum, yes, but there is no logical reason for that. This was an educated guess, and was confirmed by observation it's not a conclusion.
Einstein started to formulate special relativity theory starting from an assumption that a "ball of light" won't change its shape for non-inertial (no accelerarion) observers regardless of their respective speed. I.e. constant speed of light was the reason not a result of this theory.
(Duh. This got lenghty.)
Actually I can't even parse the first two sentences, and the third seems to refute something I never claimed.
There's no explanation "needed". Light photons move at a constant speed from any viewpoint. Its just a fact that is experimentally confirmed.
Perhaps what you need is an experiment that proves this to be true. But those experiments don't offer you any "explanation", they just will prove what you already have been told.
https://en.wikipedia.org/wiki/Relativity_of_simultaneity
------------
One thing that helped me understand it all is that "Reality" is a wave that propagates out. We call it "the speed of light", but its far more accurate to call it "The speed of reality" or perhaps "The speed of causality".
Basically, when A causes B, that "event" takes time to propagate to other locations. This means that different observers sees the event happen at different times.
For example: the galaxies 3-billion light years away from us appear to be forming today. We know the information is 3-billion years old, but reality itself is warped. Because the reality from 3-billion years ago was 3-billion light years away, its basically happening right now from our point of view (The "wave of reality" is finally reaching us).
Calling it the "speed of light" is confusing for multiple reasons. Just call it the "speed of reality" (and light in a vacuum happens to travel at this speed) and in my eyes, it becomes way easier to understand.
Hand-waving isn't an explanation, it's a distraction.
Saying that the laws of the universe don't (or can't) have explanations is not the same as saying they are intuitive to everyone. Ultimately, some of those facts you just have to accept. It is extremely difficult to have any useful analogy or explanation that attempts to explain why light always travels at the speed of light in any reference frame.
The consequences can definitely be explained well, but the fundamental laws really can't.
EDIT:
John von Neumann's quote about math reflects my view about this kind of fundamental physics:
> in mathematics you don't understand things. You just get used to them.
As another poster described: Why do Magnets attract each other, but sometimes repel each other?
Well, we can list a ton of consequences, make up stories about negative charge and positive charge (but then why do THOSE things attract / repel each other??). We can craft mathematical laws that describes the nature of this attraction.
But at the end of the day, its just a fact you have to accept. Reality has these things called magnets: they're made up of things that attract each other.
Similarly: Reality itself moves at a certain speed. Physicists call that speed "The Speed of Light". From everyone's point of view, reality propagates out like a wave, and space itself warps to keep things consistent. Its weird. But that's just how the world works.
Step 1 is accepting the fact. Step 2 is performing calculations so that we can start taking advantage of those relativistic effects in engineering and design.
Time stands still for the photon and is super slow for the particle. Super slow is still infinitely away from 0. In the article example from the particles view, 0.000..1 seconds pass for the photon to be 1cm ahead being the photon is so fast. From our view however that same small time is dilated to the 200k years.
This is what allows the photon to appear to continue to travel at the speed of light from the particles frame of reference.
If the particle was carrying a clock, and we could watch it tick as it flew away from us, it would appear to be ticking super slowly, the second hand would take forever to move.
Conversely if we had a giant clock and the particle could watch it as it flew away from us, it would appear to be ticking super fast, it would look as though we were travelling far into the future.
The same is also true if an object is close to a very large gravity well. If someone could stand next to the event horizon of a black hole and hold a giant clock, from our point of view, their clock would appear to tick very slowly. From their point of view, it would tick normally, but our clock would rapidly tick far into the future. The universe around them would quickly travel into the future.
Time and space are elastic to allow the speed of light to remain constant.
Say a particle and I are moving along like so:
Or more simplified, say two cars are moving like so: When I'm stationary, I see him go past at 100km/h. When I move at 50km/h, in the real world he would now appear to only be going 50km/h. But if I slow down my time to half speed, now he'll look like he's going 100km/h again. Because he looks to me like he's at 50km/h at double time speed = 100km/h. That seems to make sense - time slows down and the apparent speed stays at C (100km/h in this case).That's how I've understood the explanation for relativity. But it must be a very wrong understanding - because that whole idea breaks down when the other car is going along a different vector to me! In this situation:
His speed relative to me would come out as 150km/h in the real world, and no amount of making him look like he's going faster would reduce his speed to 100km/h.https://en.wikipedia.org/wiki/Lorentz_transformation
Your measurement of time and space will always adjust to ensure light travels at a constant speed.
Time dilates, length contracts. So perhaps it would "look" like the car travelled a smaller distance over a longer period of time that what you expected, from your frame of reference, versus a third observer who can see you both.
Enough with the metaphors already, the measurements don't do anything, you, or rather phyisicists and the like do measurements, and they adjust numbers normalized to c=1 because how else would you do it. There is no way to synchronize clocks because of the CAP theorem, nevermind relativity.
You are kind of like that car. You (and everything else) are always moving at the speed of light, but through spaceTIME, not through space. When you move through space you are not changing your speed through spacetime, you are only changing your direction. The faster you move through space, the slower you move through time, and vice versa.
If I am an outside observer measuring your position with a very long ruler and your time with my wristwatch, all while watching your dashboard clock, I have access to three numbers. (Your clock, my watch, your position on my long ruler.)
There are three ways to compare these numbers. If I compare my watch to your position down the ruler, I will obtain "classical speed." The behavior of this number is very confusing when it is high.
I may also compare your dashboard clock with my ruler position, or your dashboard clock with my watch. Both of these can lead to a "speed," in the sense of one number changing at a certian rate with respect to another.
If Vx is the rate of change of the ruler position with respect to your dashboard clock, and Vt is the rate of change of my wristwatch with respect to your dashboard clock, and c is the speed of light, then it turns out to be always true that c^2*Vt^2 - Vx^2 = c^2. If you graph this you will see that it is a hyperbola.
In the parent's example, the car situation would obey V(north)^2 + V(south)^2 = 100mph^2. If you graph that it is a circle, as it differs from the above by the minus sign.
Feynman talks interestingly about the nature of these facts:
https://www.youtube.com/watch?v=MO0r930Sn_8
Or perhaps it’s better to just say that the concept of reference points hits an asymptote at velocity c, so it simply doesn’t make sense to talk about the reference frame of a photon.
Does that somehow link the emission time of the two given that there is a reference frame in which they are equivalent?
What is interesting from photon's frame of reference is the image of the rest of the world.
Compare with the Wow! signal[0] for what I mean. I bet something similar happened.
[0]: https://en.wikipedia.org/wiki/Wow!_signal
Some fun facts:
* The flux of particles in this energy regime is so low that you get about 1 per square kilometer per century, so studying them necessitates doing really wild stuff like instrumenting a patch of land the size of Rhode Island.
See: https://en.wikipedia.org/wiki/Pierre_Auger_Observatory
* These particles are so energetic that in their frame the nominally low-energy photons that comprise the cosmic microwave background appear as an impenetrable gamma ray wall thats prevents them from traveling more than about 100 million lightyears. This seems like an incredible distance but in astronomical terms this means that whatever is producing them is "nearby." We also know they don't come from our own galaxy because arrival directions don't correlate to the galactic plane.
* Current consensus says that these particles probably come from very large and active black holes in the center of certain galaxies. These objects are called active galactic nuclei (AGN).
- Would the CMB be so energetic (from the proton's frame) as to create electron-positron pairs?
- If the particle can't travel more than 100m light-years, what happens to it? Does it slow down? Get destroyed? Is the answer markedly different from our reference frame vs the particle's?
To the second question: it loses energy due to pair creation (iirc, surely simplifying due to bad memory).
In a nutshell, that'll never happen. You'd have to be the unluckiest astronaut to ever live. These particles reach Earth at a rate less than 1 per century per square kilometer. So you'd have to hang out in space for like a hundred million years...
The original particle never reaches the ground. It gets annihilated in a collision some tens of kilometers up in the atmosphere.
If you were hit, I'm not sure the cascade would do significant damage before it exited your body on the other side.
I also worked in this field (Pierre Auger Observatory in the Karlsruhe group) before I "sold out" to join a tech company in late 2010. Might we have met?
Back to cosmic ray anisotropy. There was actually a big paper from the Pierre Auger collaboration in 2007 on anisotropy that made it to the cover of Science. It correlated arrival directions with a I catalog of, IIRC, AGNs. I was in my first year in the group so I didn't make the author list yet. I was quite disappointed at the time. Pretty much from the moment of publication, however, the statistical significance we got from the data started decreasing until it was no longer something we were particularly confident in. The collaboration had to publish a note on that. Ouch. We never worked out why this was happening (if other than horrible luck) before I left.
Before the publication there had been interesting internal discussions about whether to publish. The astronomers typically felt the significance was plenty by astronomy standards and we were trying to do astronomy with particles after all! The particle physicists tended to want to apply the more conservative thresholds that are common in accelerator physics. After all, what was our detector if not a giant calorimeter? :)
Do we know that it's not any of the particles we already know about? As in, is it a new kind of particle, for sure?
Or is it just an energised photon or something?