4 ms·

This doesn’t make any sense

by p1esk 4y ago

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tromp 4y ago
When you see someone standing 3m away from you, the light took 10 nanoseconds to reach your eye, so you see them as they were a very short time ago. Of course, they're only younger when measuring their age not from their birth but from the big bang.
jpollock 4y ago
I find it useful to think of photons as vector clocks: https://en.wikipedia.org/wiki/Vector_clock https://en.wikipedia.org/wiki/Vector_clock Take a photon starting from your chest and give it t1. * Assume that the speed of light is symmetrical. * When the photon hits the next person's eyes, it is t1 + distance/speed of light. Meaning, the photon is "from the past". Since all photons arriving are from the past, the photons travelling the shortest distance are the newest (representing the largest timestamp). So, the thing with the largest observable timestamp is yourself.
- p1esk 4y ago
  We are not talking about the age of photons. We are talking about the age of the thing that emits/reflects photons. The confusion arose because the OP said "you are the oldest thing in the universe you can observe". They should have said "you are the most recent thing in the universe you can observe".
  - ncmncm 4y ago
    Strangely enough, everything that emitted a photon is at least as old as that photon.
brianpan 4y ago
It's similar to how every sound you hear is of an event in the near past. Every thunderclap is caused by a past and distant lightning event. As a child, we'd see lightning and then count seconds waiting to hear the thunder (sound travels slower and takes longer to arrive than the light- about 2 seconds per mile). If you're hearing thunder now, in a way, you're hearing an event in the past. The farther the thunder traveled, the farther into the past you are experiencing. Across the expanse of space, you are not just hearing, but seeing into the past. The farther the light traveled, the farther into the past you are experiencing now.
- p1esk 4y ago
  Yeah, so I’m older than the lightning. Am I also older than the sun? By this logic, I'm the newest thing in the universe, because it takes the shortest time for me to observe myself.
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  - brianpan 4y ago
    I re-read the parent comment and I see why you're confused. It was awkwardly worded. "Older" and "younger" are confusing ways to put it. The fact is, simultaneous observations don't necessarily mean simultaneous events. If you hear 2 people shouting at the same time, but one person is very far away and one person is near, you can assume the person farther away actually shouted first. The reason this happens is the different delay across different distances. The distances have to be much greater to notice the difference with light compared to sound. But compared to the expanse of the universe, light actually travels quite slowly. If the sun disappeared, we wouldn't see it disappear on Earth for 8 minutes (that's how long it takes light to reach Earth). Essentially, we are seeing the Sun as it was 8 minutes in the past. The effect is even greater outside our solar system and even greater beyond our galaxy. We see stars and galaxies as they were, not just minutes but years and years in the past. Some stars that we see now have certainly already reached the end of their life, exploded into a supernova and collapsed. We just haven't seen it yet. The light from those events haven't reached us yet. Everything we see is of something as it was in the past. Even though we are seeing all the stars and galaxies simultaneously, the farther away it is, the farther into the past we are observing.

This doesn’t make any sense

by p1esk 4y ago

This doesn’t make any sense

deleted 4y ago

[deleted]

deleted 4y ago

[deleted]

tromp 4y ago

When you see someone standing 3m away from you, the light took 10 nanoseconds to reach your eye, so you see them as they were a very short time ago. Of course, they're only younger when measuring their age not from their birth but from the big bang.

jpollock 4y ago

I find it useful to think of photons as vector clocks: https://en.wikipedia.org/wiki/Vector_clock https://en.wikipedia.org/wiki/Vector_clock Take a photon starting from your chest and give it t1. * Assume that the speed of light is symmetrical. * When the photon hits the next person's eyes, it is t1 + distance/speed of light. Meaning, the photon is "from the past". Since all photons arriving are from the past, the photons travelling the shortest distance are the newest (representing the largest timestamp). So, the thing with the largest observable timestamp is yourself.

p1esk 4y ago
We are not talking about the age of photons. We are talking about the age of the thing that emits/reflects photons. The confusion arose because the OP said "you are the oldest thing in the universe you can observe". They should have said "you are the most recent thing in the universe you can observe".
- ncmncm 4y ago
  Strangely enough, everything that emitted a photon is at least as old as that photon.

brianpan 4y ago

It's similar to how every sound you hear is of an event in the near past. Every thunderclap is caused by a past and distant lightning event. As a child, we'd see lightning and then count seconds waiting to hear the thunder (sound travels slower and takes longer to arrive than the light- about 2 seconds per mile). If you're hearing thunder now, in a way, you're hearing an event in the past. The farther the thunder traveled, the farther into the past you are experiencing. Across the expanse of space, you are not just hearing, but seeing into the past. The farther the light traveled, the farther into the past you are experiencing now.

p1esk 4y ago
Yeah, so I’m older than the lightning. Am I also older than the sun? By this logic, I'm the newest thing in the universe, because it takes the shortest time for me to observe myself.
- deleted 4y ago
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- deleted 4y ago
  [deleted]
- brianpan 4y ago
  I re-read the parent comment and I see why you're confused. It was awkwardly worded. "Older" and "younger" are confusing ways to put it. The fact is, simultaneous observations don't necessarily mean simultaneous events. If you hear 2 people shouting at the same time, but one person is very far away and one person is near, you can assume the person farther away actually shouted first. The reason this happens is the different delay across different distances. The distances have to be much greater to notice the difference with light compared to sound. But compared to the expanse of the universe, light actually travels quite slowly. If the sun disappeared, we wouldn't see it disappear on Earth for 8 minutes (that's how long it takes light to reach Earth). Essentially, we are seeing the Sun as it was 8 minutes in the past. The effect is even greater outside our solar system and even greater beyond our galaxy. We see stars and galaxies as they were, not just minutes but years and years in the past. Some stars that we see now have certainly already reached the end of their life, exploded into a supernova and collapsed. We just haven't seen it yet. The light from those events haven't reached us yet. Everything we see is of something as it was in the past. Even though we are seeing all the stars and galaxies simultaneously, the farther away it is, the farther into the past we are observing.