# Photons and age

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1. Aug 27, 2015

### Berettaspeed

My first Post :)

I understand photons are are not going to age. But they still have a time in which they are created. Maybe this is known and Im just late. While learning about photons, right away I got he question if we can measure its born date.I mean everything decays right? So we should accurately be able measure the age then. Now my mental battle is this... photons are said to not age because of their speed. So then..... It would come to mind, it would be impossible to verify the age... or "born date" to these things in existence. So asking these things feels odd. Its like, I should not even be asking these things. But I must.

Since Im in no position to ask anyone I know, I figure I would ask here.

Also IF anyone can provide some material to help explain how a "born date" or age is found. I would like to read up on how this is done. A google search has left me empty. But then again, I have over looked answers many times while searching. I dont know why :)

MIchael

2. Aug 27, 2015

### phinds

Photons are created during many interactions so in OUR frame of reference you could, I suppose, talk about their age but age is really only meaningful in somethings frame of reference and photons don't have a frame of reference so it is not at all meaningful to talk about their age and it certainly would not be possible upon examining a photon to determine when it was created.

EDIT: to expand on this just a bit, let's look at my statement that "age" is only meaningful timeline of an object, not in some other timeline.

There is a thing called the "Twin Paradox" that you can find explained in approximately 78,000 places on the internet and what it shows is that if we both start out at 30 years old and I travel off in a very fast spaceship and then come back, we can have a situation, just for example, where you are now 35 years old and I am 33 years old. It would not make any sense to say that I am 35 years old just because YOU are 35 years old. You aged in your path through space-time and I aged in mine but we took different paths through space-time and when we meet up, I will have aged less than you. As we did this, both of our clocks ticked at one second per second, it's just that mine ticked fewer times.

Photons don't HAVE clocks, and it is impossible to assign clocks to them, so they don't have anything that can be meaningfully discussed as a age in the same sense that you and I have an age (a duration of existence in own own timeline)

Last edited: Aug 27, 2015
3. Aug 27, 2015

### ZapperZ

Staff Emeritus
The problem here is that you use the word "age" as if its meaning is obvious. It may be obvious to you, but we don't know what you have in mind. So explain what you mean by "age". You and I "age" because each day we get more wrinkles, our bones creak a bit more, we feel more aches and pains when we get up in the morning.... How would you characterize the aging of a photon?

Now, if you ask if we can measure how long a photon has existed, that a different issue, because that is simply a measurement of time since its creation.

You will learn that, in science, what you ask is sometime as important as the answer you seek. So we are always careful and we pay a lot of attention to the question itself. For many people, this forum is the first time they actually encounter such an issue, and it forces them to sit back and really asks "What exactly am I asking?"

Zz.

4. Aug 27, 2015

### phinds

@Berettaspeed , Zapper makes a very good point and one that I should have made. You'll notice that I made some attempt to clarify terms that I used (e.g. age = duration of existence in an object's own timeline) and this is because of exactly what Zapper said.

5. Aug 27, 2015

### Staff: Mentor

6. Aug 27, 2015

### Staff: Mentor

Actually, this is not true for any fundamental particle, including ones that are unstable and do measurably decay. For example, if we have a population of 1000 muons then we know that in 2.2 us about half of those muons will decay. But that decay is not dependent on how long it has been since those muons were created. In other words, it doesn't matter how many half-lives a given muon has survived, its chance of decaying in the next half-life remains 50%. It does not become more likely to decay as time goes on.

In contrast, complicated particles, like humans, do have an age. So the probability of a given human decaying in the next year does become more likely depending on how many years that human has survived. The human has internal structure which can carry "age" information. Fundamental particles do not.

So basically, my point is that the fact that a particle decays does not imply that it has an age.

7. Aug 27, 2015

### Berettaspeed

///Now, if you ask if we can measure how long a photon has existed, that a different issue, because that is simply a measurement of time since its creation.///

I forget how to "quote" on forums its been many years.

But yes this is what Im asking. I guess, I am lost as to how we can figure out when photons are created. I was thinking if they are going along with the speed of light and aging doesnt happen for a photon, I would think it would be difficult to measure these things.

I guess if we know a photon comes from our sun and reaches earth... it may be say 8-9 minutes old as a round about number.

///
In contrast, complicated particles, like humans, do have an age. So the probability of a given human decaying in the next year does become more likely depending on how many years that human has survived. The human has internal structure which can carry "age" information. Fundamental particles do not.
///

So would the speed of light change a presents in age of all complex particles? Or even faster speeds slow down a said age? and slower speeds increase "aging"?
I hope Im asking questions that make sense.
Thanks for the replies and help.

MIchael

8. Aug 27, 2015

### phinds

You use the quote button.

9. Aug 27, 2015

### Staff: Mentor

You cannot have a massive particle moving at c or faster in any frame. And massless particles cannot have internal structure.

10. Aug 27, 2015

### sophiecentaur

It has changed over the years, I think. (Monks on high stools used to do it with pens and gold leaf lol) You can only see a 'quote' button once you have highlighted a passage you want to quote. Then you get an 'insert quotes' button in your writing space, followed by a list of the passages (plural) you have selected. The system then does the top and tail for each quote. It looks after you much better than it used to. Go on - have a go.

11. Aug 27, 2015

### -Case-

I have to wonder how consistent everyone here is with the semantics employed regarding the "age" of a photon. We have all at one time or another contemplated the stars and thought about the fact that the events we can see unfolding in distant regions of space took place many, many years ago. From our perspective, a specular attitude moving in a middling way through both space and time, these photons seem very old indeed. We say that something is "ten light-years" away with a sophisticated wave and that's that. The truth as explained above is far more subtle. If you were riding with the photon your experience would be very different. You'd be moving so energetically in a space like direction, that there is literally nothing left to give for motion in a time like direction - at least that is how I've always read it.

12. Aug 27, 2015

### phinds

No, you canNOT "ride with a photon" and neither can a clock. Have you read the rest of this thread?

13. Aug 27, 2015

### -Case-

I didn't say that you could. Did you read my post, or do you just get off on being flippant and rude?

14. Aug 28, 2015