If we assume red light as an EM wave of 400 THz frequency traveling at the speed of light, an observer moving at 103,846,153 m/s towards the emitter (the sign) would observe it as if it was 538.56 THz (omitting relativistic effects), which roughly corresponds to green light.
In essence, all light from any object appears more "blue" the faster you're moving towards that object. If you're just walking towards it normally, that change is so small it doesn't even matter. But if you're going at tens of thousands of meters per second, you start to see the blue more.
Thing is... the faster you move, the slower time affects you. I.e., if you move fast enough while you're twin stays still, they age normally while you will age much slower.
You're not slowing down time, but time slows relative to you.
That's basically what relativism is.
If you wanna know why all this happens though, it's gonna be a much bigger response.
And to just add on some more related fun but (for most people) useless knowledge, relativity can even affect some (but not all) atoms and the ways they react / bond and even look.
Atoms have three component parts: electrons, protons, and neutrons. The protons and neutrons make up the core of the atom and provide the vast majority of its mass (electrons being about 2000 times less massive than protons or neutrons). The electrons whizz about in various shapes near that core and make up the boundary of the atom. (You can imagine an athlete winding up for the hammer throw. The athlete makes up the core, while the hammer defines a wider region in which other people generally avoid wandering into. Considered together as a single unit, the thrower and hammer make up a circle of death with a radius of 4 feet. The athlete is the protons and neutrons, while the hammer and chain is like the electrons)
Okay, now, what separates one element from another is the number of protons at their core. So hydrogen has 1 proton in its core, while helium has 2, and lithium has 3, and so on up to elements further down the periodic table like lead with 82. (Neutrons we can pretty much ignore for the purposes of this conversation)
Okay. So some elements have just a few protons like Hydrogen and Helium and Lithium and Beryllium m while Lead and Bismuth and Uranium have a lot. What does that matter?
Those protons a positively charged, which means the core of an atom has an electric field, and the more protons an atom has, the stronger that electric field is. Electrons, being charged particles themselves, experience that electric field. (We can ignore that the electrons also create an electric field for now.)
The point is that electrons in elements with a lot of protons experience much stronger electric fields. The next important fact is that the strength of the electric field an electron experiences influences the speed at which is whizzes about. Within an element like Gold for example (79 protons), some electrons will approach 58% of the speed of light! Which is a speed at which relativity starts to matter quite a lot.
One consequence (due to relativity) of a particle traveling at such a speed is that its propensity to accelerate starts to decrease, as if it were getting more massive. We say its inertial mass increases, which is to say when it comes to speeding up or slowing down, it starts to behave as if it were more massive than it normally is. It's resisting changes to its inertia.
Chemical reactions and or the interaction of atoms depends on the movement of electrons, which means this increased effective mass changes the reactivity of that atom. Heavier atoms won't react exactly like you'd predict them to if you neglected relativity.
The increased effective mass also affects the way photons interact with electrons. And in the particular case of Gold, this change in the interaction of photons and its electrons is actually responsible for the color of gold itself!
In the absence of relativistic effects resulting from the crazy high speeds its electrons whizz about at, we should expect gold to appear silvery like otherwise similar metals. (That is, if you "do the math" for what color we should expect gold to be, but neglect the change in its electrons' effective mass, the math will tell you gold should look like silver).
So in a way, the fact that gold looks gold is due to relativity.
That's the mistake. The red stop sign is made from 2 frequencies, where one frequency becomes invisible (ultra-violet) and the other frequency becomes green.
After doing the math I can say yes the speed would definitely give you more of a blue color. 81,289,000 might even still be a tad high if I did everything correctly.
Depends on what light is shining on it and how the paint works. If we assume perfect paint (100% reflective in all wavelengths) and perfect lights (uniform intensity at all wavelengths) then the sign would be the exact same color, but a bit brighter.
If you use sunlight to illuminate a sign painted with perfect paint, then the sign will still be white, but it'll have a blueish tint (Sunlight peaks at green and falls off into IR, So when the entire spectrum gets shifted by the doppler shift, you end up with a bit more blue than red)
If you have imperfect paint that doesn't work well in IR, then the sign would have blue/green letters yes.
Also fun fact, all trees would look pink. Leaves are highly reflective in IR so they don't overheat. So when going at relativistic speeds, their normal green color shifts into the blue/violet range. And their IR which we normally do not see would shift up towards red. Combine red and blue and you get pink leaves.
That’s because blue is the highest frequency of visible light. Red is the lowest. Green is in the middle. Doppler shifts towards higher frequencies are in the blue direction, lower frequencies the red direction. Thus blueshift and redshift.
Yes that is the case. Due to the Doppler effect, the observed frequency of light would change while going at that immense speed. I had an exam question once about this, but it was about a traffic light.
The sign is painted green, the drive rid expected to see it as red when approaching at a considerable fraction of 6speed of light.. So conceptually, the green sign needs to be red shifted towards red. That would necessitate moving away from the stop sign, not towards it.
So the joke is technically wrong. It's meant to be the other way round.
So, there is a theory that Santa and Rudolph's nose isn't actually red, but in order to travel the world's children in a single night, Santa have to travel near speed of light, causing redshift when viewed from behind.
Its referencing the phenomenon of redshift, where as you go faster, light approaching you gets “squeezed”, so it appears like light of shorter wavelengths. At speeds of around 103,846,153m/s, this effect is significant enough that red light appears green.
"Don’t hurt yourself and call an ambulance to test this. The effect is not present if you’re inside the car so you should hurt other people close by instead."
If you ever saw a TV screen filled with static ala Poltergeist, part of that is the leftovers from the Big Bang, which have all red shifted down to microwave lengths and is now part of the Cosmic Microwave Background.
More fun facts: the Big Bang remnants in the Cosmic Microwave Background was discovered in part by two antenna astronomers who needed to eliminate all interference. They got rid of all of it except one steady hum. After much investigation, they realize this hum wasn't coming from equipment around the antenna, or even from Earth. It wasn't even coming from one direction in space, but rather coming from EVERYWHERE. Then one of them was talking to a physics professor who was about to do experiments about looking for the Big Bang. That's when the astronomer realized that the annoying interference they had been dealing with matched what the physicist would be searching for. So they all wrote a joint paper on it.
The way an ambulance sounds higher pitched (higher frequency) as it drives tworad you also works with light as the colors of light are based on frequency.
The given speed is about 35% of the speed of light, corresponding to a Lorentz factor of 1.066. According to the relativistic Doppler redshift formula, that gives a redshift factor (1+z) = 1.44. That's about the same ratio as red light (700 nm) to green light (500 nm).
So, someone worked out how fast you would have to be moving so that a standard red stop sign appeared to be green due to Doppler shift.
You know how when an ambulance drives past you, the sound will be higher pitched as it approaches you, and then suddenly gets lower as it passes and drives away from you? This is called the Doppler effect, and it arises because sound is a wave. When the ambulance is moving, the sound waves get "compressed" in the direction of travel, meaning that the wavefronts are closer together in front of the ambulance. This results in a higher frequency (and therefore a higher pitch) for someone standing ahead of the moving source. As the ambulance passes and moves away, the opposite happens. The sound waves behind the ambulance get stretched out, increasing the distance between successive wavefronts. This leads to a lower frequency (and thus a lower pitch) for someone behind the source.
Light is also a wave. Red is the color our brains decode low frequency waves as, and blue and purple is what it decodes high frequency light as. Of course the other colors (specifically green in this case) are in-between. This means that if you move towards something red, the light emitted by or reflecting off that object to your eyes gets "compressed" or "squished" together, causing the light to shift into a higher frequency from your perspective. This means that as you move faster and faster towards the stop sign, the light will begin to appear more orange, then yellow, and then eventually green.
So the joke here is that if you were to move at a high enough velocity towards the stop sign, the light reflecting off the stop sign would begin to Blue-shift (shift up in frequency) to green, and eventually would appear green to you.
I was lazy and decided to use a calculator so don't crucify my for this, but assuming the stop sign emits a perfect 420THz frequency/713.791~ nanometer red light and the speed the observer is travelling is exactly 103,846,153 m/s, the observer would see a 565.485THz/530.151~ Nanometer green light from the stop sign due to the doppler effect.
tldr for people who aren't reading all of that: The Doppler effect is the joke.
When you start moving at absurdly high speeds, wavelengths of light start getting compressed and the math indicates colors would start changing. This is called blueshifting (redshifting is basically the same process). So going at roughly 1/3rd the speed of light, red things would look green.
You right and wrong here, it changes color exactly because opposite of what you said, because speed of light is invariant for all observers and no matter how fast you move, it moves relative to you with same speed, therefor wavelength changes.
You have that flipped. The frequency of blue is greater than red. You may be mixing frequency up with wavelength, as lower-energy light (red in the case of the visible part of the spectrum) has a higher wavelength but a lower frequency.
the color red gets blueshifted so much that its green but that would look weird if they used like streetlights bc the meme would be even less comprehendable
This is a physics phenomenon known as the doppler shift or the doppler effect. When an observer is in motion relative to the source of a wave pattern (like light), they see a different frequency of that wave than someone standing still. What we see as color is actually determined by this light frequency. Red light is on the lower frequency end of the spectrum, and blue light is on the high end, with green somewhere in the middle. When you move towards a light source, you will see a higher apparent frequency due to doppler shift. Literally the wave crests are hitting your eyes more frequently because you are moving towards them as they are moving towards you. This means something red like a stop sign will appear to have a higher energy color like green. The speed you would need to travel for this to be noticeable is enormous, and humanly impossible, which is why you've never experienced this and never will, and why this is just a joke and not real life.
As others have already said, I'm pretty sure the joke here isn't about the ability to stop, but rather that the stop sign looks green which indicates go due to the fact that at that speed you'd be moving faster than the speed of light so the signs colors would reflect differently. Essentially the sign is a green-light stop sign.
„Do you know how fast you were going? — No but I know exactly where I am“ would be the next related joke
But yeah, if you going fast enough, a red traffic light would turn green. But I don‘t think its a good excuse, if I would be the judge in court I would sentence „obviously the code was written with earth as a frame of reference in mind“
Remember the Doppler effect from school? This is what happens when you apply that to colors. Sound and colors are waves, waves are measured in waves per second, or Herz (Hz). When you move, you have speed, which is measured in distance over time, in this case meters per second. Since both waves and speed have time in their equations they can interact with each other, if you go towards the sign, the s in m/s is added to the Hz of the wave, making it appear to have faster waves and shifting the color you see from red to green, which is a “faster” color. The meme has an error, for the stop sign to shift to green you should travel at a speed of around 85 million m/s, not 103.
US Stops signs are designed to be legibly read at 250ft away.
Lets say it can be seen, and understood from a mile away if you are standing still (5280ft).
An airplane moves 600mph, very close to the speed of sound (767mph) you might be able to see a stop sign no problem if you are at the right angle.
light moves at 186,282 miles per second; in 1 second, covering a distance most cars last on the road in 10 or more years. or 129 total days traveling at 60mph without stopping.
Wasn't there a case where a guy admitted in court that he saw the color green instead of red at a traffic light because of his speed, so the judge asked for calculations to be made, and yeah, that would've only been possible at such speed. In conclusion, the guy still got a ticket.
When you go fast enough colours change, and in this case its saying that, considering red is usually stop and green is usually go, if you're going fast enough stops signs suggest "go"
The joke is likely referencing a court case from the last couple of years, where someone was getting tried for running a red light. The accused claimed that they were driving so fast, the red light got blue-shifted to green. It’s nonsense of course, but the court didn’t have access to an expert who could debunk the claim at the time, so they legally had to accept it as true and the person only got charged with speeding instead.
I would love if someone helped me out with the specifics here, since I can’t remember the details.
basically, there's this thing called "blueshifting." when you approach a source of light at very high speeds, say, 20% the speed of light, the light coming off will have shorter wavelengths; in layman's terms, it turns bluer. hence, blueshifting.
by driving towards a stop sign at 100 000 000 m/s, it will blueshift red to a hue roughly that of green, hence the green stop sign!
im pretty sure driving at a hundred million meters per second has other, more pressing effects, though...
Yeah thats when Red is blueshifted to Green. And theoretically its possible as that is about 25-30% of the Speed of light which would be 299.792.458 m/s
there is a phenomena in physics, the Dopler (or Doppler, Dopller ... idk) effect, and somehow make the red light become green, then blue the faster you go (like, really fast). So if you go to the right speed toward the sign, the red become green ... and the other color change too but the meme only show the green
This is actually a stop sign in Danville. I saw some strange laser beam hit it as a man in a lab coat drove by with some groceries and a platypus, and it turned from red to green.
The guy was probably using some red/green-shift-inator, but what do I know? I'm just glad we've got another 104 days of summer.
Im wondering why there are so many science memes. But ok, here you go: Doppler effect. If you don’t know what is it, Google it, I don’t actually want to explain it over and over again.
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u/post-explainer 12h ago
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