Hardcore Physics Discussion

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.
R

RickyScott

Full Member
Verified Member
7+ Year Member
Joined
Oct 4, 2017
Messages
5,217
Reaction score
10,220
elementaryschooleconomics said:
Oh yes...I've practiced in areas around Navy bases/nuclear plants....they always ask their dose in Sieverts.
Click to expand...
Also had a particle physicist, but he didn’t want to know anything technical. I asked him how photons can carry momentum despite being massless.
Members don't see this ad.
 
RickyScott said:
Also had a particle physicist, but he didn’t want to know anything technical. I asked him how photons can carry momentum despite being massless.
Click to expand...
The mass(less) thing can be rationalized by considering that they have energy and that energy can impact the motion of massive particles, so they must have momentum

The thing that boggled my mind is… photobs have no age. By virtue of special relativity, no time can pass for a photon, since it is traveling at the speed of light. That means, from the photon’s perspective, the instant they are formed is the same instant as the moment they are consumed. 🤯
 
Last edited:
Members don't see this ad :)
Lamount said:
The mass(less) thing can be rationalized by considering that they have energy and that energy can impact the motion of massive particles, so they must have momentum

The thing that boggled my mind is… photobs have no age. By virtue of special relativity, no time can pass for a photon, since it is traveling at the speed of light. That means, from the photon’s perspective, the instant they are formed is the same instant as the moment they are consumed. 🤯
Click to expand...
So it goes.
 
Lamount said:
The mass(less) thing can be rationalized by considering that they have energy and that energy can impact the motion of massive particles, so they must have momentum

The thing that boggled my mind is… photobs have no age. By virtue of special relativity, no time can pass for a photon, since it is traveling at the speed of light. That means, from the photon’s perspective, the instant they are formed is the same instant as the moment they are consumed. 🤯
Click to expand...
Photons don’t impart momentum to most of the known mass in the universe. This is a huge mystery.

“From the photon’s perspective” … I have never liked. Very anthropomorphic. I know there are web links that will refute this view. But who knows what photons experience. Speaking of special relativity, age is very relative. I could age just a microsecond while all the stars in the galaxy died out (with a fast enough ship).

Photons don’t always travel at the speed of light. In water, photons travel about 70% the speed of light… that’s why there’s a blue glow in the water in nuclear power plants, or why whole brain RT patients see light flashes. (Also future rad oncs may capitalize on sub-c photons in interesting ways.) Speaking of anthropomorphizing, some used to think photons were “choosing” their paths through space, and this was one way of explaining Fermat’s principle of least time. Now no one thinks that, but we have to be careful guessing what a photon experiences or “thinks.” There could be pockets in the universe, say inside black holes, where the notion of photons not aging may get flipped on its head. Another great mystery.
 
Last edited:
You can't really conceptualize quantum mechanics. It doesn't make sense, even though experimentally it checks out. Wave - particle duality and collapse of the wave function upon measurement ("measurement problem"), doesn't make intuitive sense.

When Heisenberg was still a young lad (before the Nazi's ruined him) Neils Bohr gave him some good advice about describing quantum mechanics "What is it that we humans depend on? We depend on our words... Our task is to communicate experience and ideas to others. But when it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images and establishing mental connections." i.e. we use our words and imagination as a mental framework to help understand what is happening, but its probably not what is actually happening.
 
TheWallnerus said:
Photons don’t impart momentum to most of the known mass in the universe. This is a huge mystery.

“From the photon’s perspective” … I have never liked. Very anthropomorphic. I know there are web links that will refute this view. But who knows what photons experience. Speaking of special relativity, age is very relative. I could age just a microsecond while all the stars in the galaxy died out (with a fast enough ship).

Photons don’t always travel at the speed of light. In water, photons travel about 70% the speed of light… that’s why there’s a blue glow in the water in nuclear power plants, or why whole brain RT patients see light flashes. (Also future rad oncs may capitalize on sub-c photons in interesting ways.) Speaking of anthropomorphizing, some used to think photons were “choosing” their paths through space, and this was one way of explaining Fermat’s principle of least time. Now no one thinks that, but we have to be careful guessing what a photon experiences or “thinks.” There could be pockets in the universe, say inside black holes, where the notion of photons not aging may get flipped on its head. Another great mystery.
Click to expand...

Photons impart momentum to all baryonic matter ("visible matter) in the universe (i.e. electrons, protons)... I wouldn't call dark matter to be "known mass", but that is obviously debatable

Perspective is the essence of relativity. It wasn't meant to be anthropomorphic... it's just the term "reference frame" is clunky.

Technically, when photons enter a medium, they are no longer just photons. They are either directly absorbed and readmitted after delay, or they form a combined quantum state with the electrons present in the medium, which can have different properties than the photons alone. The photons themselves don't travel slower than the speed of light, but the net velocity of the beam of light can be slower.
 
metallica81788 said:
Nerds
Click to expand...
nerds GIF
 
Lamount said:
Photons impart momentum to all baryonic matter ("visible matter) in the universe (i.e. electrons, protons)... I wouldn't call dark matter to be "known mass", but that is obviously debatable

Perspective is the essence of relativity. It wasn't meant to be anthropomorphic... it's just the term "reference frame" is clunky.

Technically, when photons enter a medium, they are no longer just photons. They are either directly absorbed and readmitted after delay, or they form a combined quantum state with the electrons present in the medium, which can have different properties than the photons alone. The photons themselves don't travel slower than the speed of light, but the net velocity of the beam of light can be slower.
Click to expand...
"Reference frame" is very clunky for a photon. All the Lorentz transformations (mass, time, length) go to zero at v=c. What does a "zero reference frame" really mean? No one has ever explained this to me. (Also no one has ever full explained to me what it means that the unit gray of radiation absorbed dose reduces to units of c-squared... which also means the highest dose of radiation absorbable in any matter is 1 c-squared which equals 8.99E16 gray.) Photons may "age" or "experience" time; David Bohm said all of matter is condensed light after all. If a photon had no time in which to interact with matter, or convert into matter, how could it ever do so? Do electrons experience time?

z5TTl1J.png
 
A a
TheWallnerus said:
"Reference frame" is very clunky for a photon. All the Lorentz transformations (mass, time, length) go to zero at v=c. What does a "zero reference frame" really mean? No one has ever explained this to me. (Also no one has ever full explained to me what it means that the unit gray of radiation absorbed dose reduces to units of c-squared... which also means the highest dose of radiation absorbable in any matter is 1 c-squared which equals 8.99E16 gray.) Photons may "age" or "experience" time; David Bohm said all of matter is condensed light after all. If a photon had no time in which to interact with matter, or convert into matter, how could it ever do so? Do electrons experience time?

z5TTl1J.png
Click to expand...
At 22:30 why light doesn’t experience time conceptual explanation about the reference frame. Equations are clear- if everything moves through spacetime at the speed of light means that if something is moving through space at the speed of light, it is moving through time with 0 speed.
 
Last edited:
RickyScott said:
A a

At 22:30 why light doesn’t experience time conceptual explanation about the reference frame. Equations are clear- if everything moves through spacetime at the speed of light means that if something is moving through space at the speed of light, it is moving through time with 0 speed.
Click to expand...

Sean still didn't explain it well 🙂 Yes I know the Lorentz transformations mean when v=c, time dilates to zero. I would measure the time a photon goes from my finger to the moon's surface at ~1.5 seconds but in the photon's frame it would be zero elapsed time along its trajectory as Sean says. But this raises paradoxes and is a window into the disagreements between quantum mechanics and general relativity. "Zero elapsed time" is less than Planck time... a paradox. If I could watch a photon travel an infinite distance, or for an infinite amount of time, the Lorentz transformation for that is indeterminate. So is the universe not infinite? Is time not infinite? Who knows, but the equations of relativity give non-understandable answers when calculated for infinite distance or time. And this means, to me, that the phrase that a photon can "move... with 0 speed," through time, is also non-understandable. Moving with zero speed is not really moving!
 
TheWallnerus said:
"Reference frame" is very clunky for a photon. All the Lorentz transformations (mass, time, length) go to zero at v=c. What does a "zero reference frame" really mean? No one has ever explained this to me. (Also no one has ever full explained to me what it means that the unit gray of radiation absorbed dose reduces to units of c-squared... which also means the highest dose of radiation absorbable in any matter is 1 c-squared which equals 8.99E16 gray.) Photons may "age" or "experience" time; David Bohm said all of matter is condensed light after all. If a photon had no time in which to interact with matter, or convert into matter, how could it ever do so? Do electrons experience time?

z5TTl1J.png
Click to expand...
You can derive E=mc2 from Lorentz transformations alone (which can be derived by taking results of Michelson-Morley experiment at face value). No matter how fast you go, light is always traveling by you at the speed of light. Feynman Lectures Volume 1, chapter 15 (free online) will take you through it.

E=mc2---> A Gy is E per unit m or E/m---> Gy is measured in c2
 
I saw hardcore and thought it was for something else… I was very disappointed!
 
RadOncDoc21 said:
I saw hardcore and thought it was for something else… I was very disappointed!
Click to expand...
Something tells me there is one of those movies where the title is a play on Schrodinger’s Cat. But I digress.

All the talk about relativity and perspective ignored the relativity. If you travel at the speed of light for a minute, you would perceive it as a minute. It’s everyone else not going that fast that would perceive it as 10,000+ years. Similarly, if you fall cross a black hole’s event horizon you will fall in. You will only appear frozen to an outside observer.

I’ll say it right now…you can’t carry a physics nerd card if you have not read An Elegant Universe for fun. Doing that to relax on vacation was when I realized I just how deep I was in.
 
TheWallnerus said:
"Reference frame" is very clunky for a photon. All the Lorentz transformations (mass, time, length) go to zero at v=c. What does a "zero reference frame" really mean? No one has ever explained this to me. (Also no one has ever full explained to me what it means that the unit gray of radiation absorbed dose reduces to units of c-squared... which also means the highest dose of radiation absorbable in any matter is 1 c-squared which equals 8.99E16 gray.) Photons may "age" or "experience" time; David Bohm said all of matter is condensed light after all. If a photon had no time in which to interact with matter, or convert into matter, how could it ever do so? Do electrons experience time?

z5TTl1J.png
Click to expand...
The mass thing can be thought of this way...
Einstein demonstrated that all matter two forms of intrinsic energy -kinetic energy associated with motion, and rest energy associated with mass. A photon simply ONLY has kinetic energy. If it did have mass, it couldn't travel at the speed of light... the way that relativity is argued, to say something travels at the speed of light is synonymous with saying it has no mass

Length translating to 0 is not terribly bothersome to me because we are talking about a point particle anyway. On the other hand, if a ruler stick were going 99.99999999% c and there were a spider running across it at 1m/s, to an observer, it would be going faster than c… so from that observer’s perspective, the ruler stick is always squished enough that the spider never goes faster than c.

The time translating to 0 is the interesting point that I brought up. Relativity would explain this by saying that ALL matter moves through space-time at exactly the speed of light. Think of space velocity and time "velocity" as the X and Y axis (respectively) and that every particle in the universe is a vector of the same magnitude (i.e. has the same "speed"). For things with a relativively low space velocity, the vector has a steep slope, moving mostly through time. Things whose space velocity is close to the speed of light have a shallow slope, moving mostly through space (and moving much less through time). A photon's vector is pointed rightward, moving ENTIRELY through space, and not AT ALL through time.
 
You must log in or register to reply here.
Top