# Speed of light vs speed of vision

Discussion in 'Physics' started by Willen, Oct 22, 2017.

1. ### Willen Thread Starter Member

Nov 13, 2015
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I know sound of distance lightning strike is not exact in time. We hear the sound many seconds later after the real strike. So in other word, the sound is not real lightning strike event. It means sound takes time to travel and what we hear from distance is not real. It also means our hearing has delay as speed of sound.

Same way, light takes time to travel. Does it mean our vision has delay as speed of light?

If so then if a star shining in the sky from 1 light year far, collapse today however we will be seeing the star till another year?

Does this mean what we see in the sky (with eye or with Hubble Telescope) is not exactly real? Maybe we are seeing some stars shining which might not even exist in the sky (collapsed years ago).

Last edited: Oct 22, 2017
2. ### MrChips Moderator

Oct 2, 2009
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Nothing is "real".
Everything we observe and experience is a thing from the past.

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3. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Here's a good example. Just recently detected: the death of two neutron stars which happened 130 million years ago!

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4. ### OBW0549 Distinguished Member

Mar 2, 2015
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"What is reality???"

All joking aside, I think it's pointless to worry about whether something you're seeing or hearing is "real" or not, and just recognize that both light and sound travel at finite speed (sound at roughly 300 meters/sec and light at about 300,000,000 meters/sec). As a result, anything we see or hear is necessarily something that happened in the past, whether a few microseconds or milliseconds ago, or billions of years ago. There's nothing more to it than that.

Last edited: Oct 22, 2017
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5. ### Willen Thread Starter Member

Nov 13, 2015
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Ok, then if any aliens 100 millions light year far from us are observing the earth then they are seeing dinosaurs in the earth instead of humans. Because their vision has 100 billions light year delay. Joke or true?

Additional imagination: If science found faster way of travel than the speed of light then we would reach 200 light year far within few hours and would see live of 200 years ago how the earth and our grand parents was going on.

6. ### AlbertHall AAC Fanatic!

Jun 4, 2014
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There is also a processing time in the brain which is faster for sound than for light. If a car switches on its headlights and sounds the horn at the same time and you are far away you will see the lights before you hear the sound as with thunder. However if you are near the car the opposite will be the case because of the greater delay in the brain processing the signal from the eyes.

Reality is an illusion created for us by our brain.

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Jul 18, 2013
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Same as the car horn appearing to changing pitch as it nears you, Doppler effect.
Max.

8. ### dl324 AAC Fanatic!

Mar 30, 2015
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Your notion of "delayed" vision is going to trip you up.

What we see depends on the speed that light propagates and the time it takes for us to interpret what we see. If these aliens 100 million light years away are observing earth. They would be seeing light that took 100 million years to get to them. There is no way for them to see what is happening now.

BTW, it's unlikely that they would have been able to resolve anything as small as a dinosaur. For the same reason that we couldn't if if we were looking at light from their planet. It would be swamped out by the light from their star.

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9. ### crutschow Expert

Mar 14, 2008
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You need to be fairly close for that to happen, from my experience.
For security, our bank has a short (about 12-15 feet) two-door glass hallway to get in and out of the bank.
The first door has to close before the second door-latch is released to open (indicated by a light going from red to green).
You can walk to the far door before the first door closes, and I've noticed that I can see the light go to green slightly before I hear the sound of the first door closing behind me.

10. ### jovit32 New Member

Oct 19, 2017
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I think If aliens are watching us from 100 millions light year away, they can see the present state of earth. As for the times when there are dinosaurs, there is a possibility that the light from that time is still traveling.

Time = Distance / Speed, If you have incredible speed like the flash. You can minimize the value of time, but time can never be equal zero. The flash is fast but one thing he can't outrun is time.

If you want to go to the past, the value of Time in the equation should be negative. How can someone do that?

Just saying.

11. ### BR-549 AAC Fanatic!

Sep 22, 2013
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The center of our galaxy could have super duper nova-ed over 20k years ago....and we would not know it.

12. ### MrAl AAC Fanatic!

Jun 17, 2014
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Hi there Willen,

Yes, light takes time to reach us from any place in the universe, including two feet away from us. But that light takes very little time to reach us while star light takes much time to reach us. If our star exploded it would take 8 minutes for us to see it because of the distance between us and it and the speed of light. It takes light 1 second to travel 300 million meters so some light burst 3 billion meters away takes 10 seconds to each us and some light burst 30 billion meters away takes 100 seconds to reach us and 300 billion 1000 seconds, etc., etc.
Since some stars are so very far away, it takes a very long time for their light to reach us. The light from the farthest stars to be seen takes about 14 billion years to each us so they could have died out already. This means we see their existence as it was when the light we see first left them. This means we see what happened shortly after what is sometimes called The Big Bang and that can be used to investigate.

The speed of light is not the only factor though. Since the universe is still expanding we may see the light from some stars go dim even though they are still in existence. That could happen if the universe expands faster or equal to the speed of light. If it can expand even near the speed of light it could take trillions and trillions of years to reach us, which means Earth wont be here anymore to see it anyway.

Who knows what the future could bring though. Invention is somewhat arbitrary, so we never know what could come up tomorrow. Faster travel, the ability to see into the past (although not relive it) are all possibilites and there are more.

So next time you look up into the night sky, keep in mind you might be seeing light that left a star before man existed or even before the Earth existed.

There's a trick for lightning, i am not sure if you have heard this one before or not.
If you see a flash of lightning start counting seconds until you hear the strike. The flash of light is observed almost instantaneously for any reasonable distance away, yet the speed of sound is only roughly 0.2 miles per second, so over 5 seconds the distance is about 1 mile. So if you hear the sound 10 seconds after the flash of light, the strike was about 2 miles away. 15 seconds about 3 miles, 20 seconds about 4 miles, etc.
This can help figure out if a storm is moving closer to you or is moving farther away over time.

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13. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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Yet, our minds, to some extent, can extrapolate forward into time to present us a picture of how things are -- as opposed to how things were.

It has been scientifically proven* that a batter cannot hit a fastball. The milliseconds required to perceive and act upon the pitch exceed the time it takes the ball to reach the batter.

Yet, good batters hit fastballs everyday -- enough so that luck is removed from the equation.

*I wish I could remember the source. It was a very interesting article.

14. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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15. ### GopherT AAC Fanatic!

Nov 23, 2012
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Average hits per game... 8.5
https://www.teamrankings.com/mlb/stat/hits-per-game

62% of pitches are strikes
http://grantland.com/the-triangle/debunking-mlb-first-pitch-strike-myth/

Pitches thrown per game.. 145
https://www.baseball-reference.com/blog/archives/7533.html

Ground outs and fly outs per season (divide by 182 to get per game stats...) about ... 18
https://www.sportingcharts.com/mlb/stats/team-pitching-ground-ball-fly-ball-ratio/2015/

So, the batter can make contact and move the ball into fair territory (or fly out into foul territory where it can be caught)

In reality, 8.5 hits per 95 strikes per game, or 1/11.

In the end, it is more a question of timing and hope. Not accuracy of swinging at the right elevation. If it was accuracy, the hit contact ratio would be much higher.

A pitcher throws a 3” ball at a 2.5” bat - the batter gets about a 3.5” window. If you only make a base hit 1/11 of strikes, it is hard to believe the batter is really seeing the ball and hitting it on purpose.

If you want to include all “hits” into fair territory, then about 1/4 strikes are hit. Still not a rate I would call intentional.

I would surmise that timing is currently more of a factor in a batter’s success than intentionally hitting the ball at a particular spot. Timing goes all the way back to studying a pitcher’s “tells”and pitching speed as they wind up and release. Unlike Joeys assumption, Luck does play a significant factor in the contact and “seeing” is mostly luck.

16. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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If you average across all batters, yes, it can look like luck that anyone hits a ball at all.

The best batters are far more productive against fastballs than the average. The distribution curve has a "long tail".

Ted Williams must have been the luckiest ball player ever.

17. ### DickCappels Moderator

Aug 21, 2008
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Digesting all of the above,light that was reflected earth 125 million years ago would contain informatiion about earth 125 million years ago. Unless... of course, you are from a state that teaches creationism, in which case the oldest light ever reflected from earth is only about 6,000 years old.

18. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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I find it instructive that, as a moderator, you would choose to start a religious (and political!) debate in an otherwise scientific thread.

Do you intend to lock it when the inevitable flaming starts?

19. ### GopherT AAC Fanatic!

Nov 23, 2012
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He was just good at reading a pitcher’s timing. And, the art of pitching was not nearly as refined as it is today. He was just ahead of his time. The reporters that wrote about him liked to claim much more about Williams than Williams claimed about himself. He was smart in an arena of jocks. Not difficult to stand out in those days.

20. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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This is only half the battle. The other half is knowing not just "when" the ball will be, but also where.

The fact that some do it exceptionally well, IMHO, illustrates the human mind's capability of extrapolating the "past" into the present. This was my only argument -- and the only point I was trying to make.

If you don't mind, I'm gonna get back to watching the ballgame now.