Immeadiacy of sensory experience

[dingansich]

Hi.. In astronomy we know that when we observe a distant star that we are seeing it the way it looked a long time ago, how long is dependent on the speed of light and the distance between us and that star. It might not even be in existence anymore. Does physics apply the same logic to our "everyday sensory experience? As I sit here looking across the room at a picture in a frame, even though the distance is small, am I seeing it as it was in the very near past? would a phycisist tell me that is an immeadiate experience of the picture frame as it actually "is", as opposed to "was?"

thanks.. ding.

 

[DaveC426913]

As I sit here looking across the room at a picture in a frame, even though the distance is small, am I seeing it as it was in the very near past?

Yes.

Would a phycisist tell me that I would be having an immeadiate experience of the picture frame as it actually "is" as opposed to "was, or vice versa?"

No. Since the speed limit of the universe is c, and nothing can reach you faster than that, a physicist will tell you it's meaningless to talk about this "is" as if it were accessible. It isn't.

 

[Evo]

Hi.. Hopefully I have found the correct forum for this inquiry. In astronomy we know that when we observe a distant star that we are seeing it the way it looked a long time ago, how long is dependent on the speed of light and the distance between us and that star. It might not even be in existence anymore. Does physics apply the same logic to our "everyday sensory experience? As I sit here looking across the room at a picture in a frame, even though the distance is small, am I seeing it as it was in the very near past? would a phycisist tell me that is an immeadiate experience of the picture frame as it actually "is", as opposed to "was?"

thanks.. ding.

There is always a very small delay in our brain processing an image, but it's so minute that when you see something it's virtually in real time.

And this isn't philosphy, so I've moved it.

 

[dingansich]

Yes.

No. Since the speed limit of the universe is c, and nothing can reach you faster than that, a physicist will tell you it's meaningless to talk about this "is" as if it were accessible. It isn't.

Thanks for the response Dave. So the would he/she tell me it is meaningless to talk about the star as it "is" currently also?

 

[dingansich]

There is always a very small delay in our brain processing an image, but it's so minute that when you see something it's virtually in real time.

And this isn't philosphy, so I've moved it.

Sorry about the post but I am new and not sure of correct category. Quick question though because I believe it is philosophical. Am I correct in thinking that not only is there a delay in respect to internal processing but also a second delay in respect to transmission of light?

light emitted from object > distance and time traveled to eyes > processing time > sensory experience.. it seems to be at least 2 durations of time in between emmitting of light by object and the ultimate experience.

 

[Evo]

Sorry about the post but I am new and not sure of correct category. Quick question though because I believe it is philosophical. Am I correct in thinking that not only is there a delay in respect to internal processing but also a second delay in respect to transmission of light?

light emitted from object > distance and time traveled to eyes > processing time > sensory experience.. it seems to be at least 2 durations of time in between emmitting of light by oblect and the ultimate experience.

Yes, the image has to hit first. That's part of the negligible delay at such a short distance.

It's science, it can be measured, what's philosophical?

 

[dingansich]

Yes, the image has to hit first. That's part of the negligible delay at such a short distance.

It's science, it can be measured, what's philosophical?

Isn't there some kind of discourse related to this somewhere in the philosophy of perception or some similar field of thought in philosophy? This chain of events and processes that you lump together take place both in the mind and the external world right?

 

[epenguin]

The processes you sweep under the carpet with the word "see" take and last vastly longer than the time the light takes to cross the room so the physicist as such has not much to tell you about them.

 

[pervect]

Thanks for the response Dave. So the would he/she tell me it is meaningless to talk about the star as it "is" currently also?

The physicist would most probably tell you that the notion of simultaneity, the set of points in space-time which are defines as being "now" depends on the observer - in particular on his state of motion.

At least this one would. Others might give you different answers.

 

[DaveC426913]

This chain of events and processes that you lump together take place both in the mind and the external world right?

Sure but it's still not philosophy. It's bio-physiology. The signals are electrochemical in nature.

 

[dingansich]

The processes you sweep under the carpet with the word "see" take and last vastly longer than the time the light takes to cross the room so the physicist as such has not much to tell you about them.

It is odd you say that because a large portion of the thought experiments dedicated to the relativity of simultaneity incorporate "SEEING". I just have never heard any physicist account for that small amount of time dedicated to transmission of light in those thought experiments. Granted it is inconsequential to the types of motion we experience daily but when a phycisit deals with objects moving at near light velocities it could become a problem if not accounted for right?

 

[dingansich]

The physicist would most probably tell you that the notion of simultaneity, the set of points in space-time which are defines as being "now" depends on the observer - in particular on his state of motion.

At least this one would. Others might give you different answers.

Thanks for the time pervect.. as you were typing I was bringing that notion of RoS up in the following post :)

 

[Evo]

Isn't there some kind of discourse related to this somewhere in the philosophy of perception or some similar field of thought in philosophy? This chain of events and processes that you lump together take place both in the mind and the external world right?

If you want to research the philosophical wanderings, you can do so, but in order to post in philosophy, you will need to follow the guidelines in both sets of rules stickied at the top of the philosphy forum.

 

[DaveC426913]

It is odd you say that because a large portion of the thought experiments dedicated to the relativity of simultaneity incorporate "SEEING". I just have never heard any physicist account for that small amount of time dedicated to transmission of light in those thought experiments. Granted it is inconsequential to the types of motion we experience daily but when a phycisit deals with objects moving at near light velocities it could become a problem if not accounted for right?

Thought experiments are idealized. Observers are points, distances are optimal. If it has no effect on the experiment, it is inconsequential.

 

[dingansich]

Sure but it's still not philosophy. It's bio-physiology. The signals are electrochemical in nature.

Thank you for the suggested avenue of pursuit.. I will spend some time in the literature tonight!

 

[dingansich]

Thought experiments are idealized. Observers are points, distances are optimal. If it has no effect on the experiment, it is inconsequential.

Really? http://books.google.com/books?id=gQ...i=tondSZLWOpnGywTa_pHyDg#v=onepage&q&f=false"

In Einstein's thought experiment Speed of Light(SoL) is accounted for in the case of the experience of lightning but the Sol in respect to the rays of light emitted from the surface of the train are not mentioned. Why is that?

 

[DrGreg]

It is odd you say that because a large portion of the thought experiments dedicated to the relativity of simultaneity incorporate "SEEING". I just have never heard any physicist account for that small amount of time dedicated to transmission of light in those thought experiments. Granted it is inconsequential to the types of motion we experience daily but when a phycisit deals with objects moving at near light velocities it could become a problem if not accounted for right?

The language that is used to describe thought experiments can sometimes be ambiguous. When people talk about what an observer "observes", or an observer's "point of view", they often don't mean what the observer would see with their eyes. It is assumed that the observer makes a calculation to account for the time delay for signals to travel; or instead you can imagine that when an event occurs there is a little clock next to it, synchronised to the observer's clock, so that the observer can read the clock and allow for the time delay.

(The complication in relativity is that different observers disagree about how to synchronise clocks.)

 

[DaveC426913]

In Einstein's thought experiment Speed of Light(SoL) is accounted for in the case of the experience of lightning but the Sol in respect to the rays of light emitted from the surface of the train are not mentioned. Why is that?

Because, in one case, it is relevant, in the other it is not.

If you are not grasping why the rays of light emitted from the surface of the train are not relevant to the experiment, I'm afraid we're going to have a lot of trouble helping you further.

 

[epenguin]

It is odd you say that because a large portion of the thought experiments dedicated to the relativity of simultaneity incorporate "SEEING". I just have never heard any physicist account for that small amount of time dedicated to transmission of light in those thought experiments. Granted it is inconsequential to the types of motion we experience daily but when a phycisit deals with objects moving at near light velocities it could become a problem if not accounted for right?

When you read physicists talk of "seeing" do not take it literally, no more than if you read them saying an electron or something "feels" a force. Well I think they will confirm this.

As Bertrand Russell observes in "The ABC of Relativity" the "observers" they talk of do not need to be human, who have their limitations when it comes to timing flashes emitted by another observer or themselves. The job can be done by suitable instruments and recorders, you can pick up the results afterwards.

Humans are IMHO an unwelcome distraction when relativity stuff is hard enough to understand anyway and I wonder if I am the only one who hates Alice, Bob and Charles and the silly signals they send each other?

BTW when I said you swept "see" under the carpet I did not mean you could do otherwise because no one can. "Seeing" is scarcely understood neurophysiology, quite different from well understood physics.

 

[Jimmy Snyder]

The speed of light is finite and so under reasonable conditions, there will be a delay from the time that a photon leaves the picture frame until the time that it reaches your eye. However, the speed of light in air is slower than the speed of light in a vacuum. Therefore, there is a frame of reference in which there is no time delay. If you were traveling in that frame, your clocks would register the fact that the emission of the photon and it's collision with your eye occurred at the same time in that frame. You would need an enormous amount of energy to attain that frame and so it is impractical to attempt this trick. None the less, there is no physical law that prevents it. There would still be a processing delay as your brain turned the photons into a mental image.

 

[DaveC426913]

Therefore, there is a frame of reference in which there is no time delay. If you were traveling in that frame, your clocks would register the fact that the emission of the photon and it's collision with your eye occurred at the same time in that frame. You would need an enormous amount of energy to attain that frame and so it is impractical to attempt this trick.

Wait. Did you just claim that - if you had an enormous amount of energy - you could travel at the speed of a photon?

None the less, there is no physical law that prevents it.

Yes there is. No object with mass can achieve the speed of light.

 

[berkeman]

The speed of light is finite and so under reasonable conditions, there will be a delay from the time that a photon leaves the picture frame until the time that it reaches your eye. However, the speed of light in air is slower than the speed of light in a vacuum. Therefore, there is a frame of reference in which there is no time delay.

I don't think that last part is correct, Jimmy.

 

[Jimmy Snyder]

The speed of light in air is less than the speed of light in vacuum. There is no reason why you cannot travel faster than the speed of light in air. This is the reason behind Cherenkov radiation.

 

[mrspeedybob]

If you are looking at a picture frame 3 meters away you are seeing it as it was 1/1,000,000 of a second ago.

Actually 1/1,000,000 of a second is the time it takes for the light to get from the picture frame to your eye. The time it takes for your eye to register the light + the time it takes to transmit the image from your eye to your brain + the time it takes for your brain to process the image and make you aware of the picture frame is 5 or 6 orders of magnitude greater then the time it takes for the light to reach you.

 

[dingansich]

Because, in one case, it is relevant, in the other it is not.

If you are not grasping why the rays of light emitted from the surface of the train are not relevant to the experiment, I'm afraid we're going to have a lot of trouble helping you further.

maybe this is my difficulty... if you can explain or point me in the right direction to learn about this I am all ears. Thanks in advance.

 

[berkeman]

Hi.. In astronomy we know that when we observe a distant star that we are seeing it the way it looked a long time ago, how long is dependent on the speed of light and the distance between us and that star. It might not even be in existence anymore. Does physics apply the same logic to our "everyday sensory experience? As I sit here looking across the room at a picture in a frame, even though the distance is small, am I seeing it as it was in the very near past? would a phycisist tell me that is an immeadiate experience of the picture frame as it actually "is", as opposed to "was?"

thanks.. ding.

Please do not multiple-post your question across the PF forums. Your 3 duplicate threads have been merged into this one.

 

[khemist]

The speed of light in air is less than the speed of light in vacuum. There is no reason why you cannot travel faster than the speed of light in air. This is the reason behind Cherenkov radiation.

Actually from another post a while back, it doesn't actually travel slower, but it will seem to have a slower speed in a medium becausethe photon is absorbed and re-emitted by atoms in that medium.

 

[DaveC426913]

The speed of light in air is less than the speed of light in vacuum. There is no reason why you cannot travel faster than the speed of light in air. This is the reason behind Cherenkov radiation.

Oh I see what's you're saying.

(Didn't think you'd make that kind of mistake...)

 

[dingansich]

can someone furnish me with the concept(s) to study about why light from an object travels differently than one from a source like a star, flashlight, or lightning strike?

 

[DaveC426913]

can someone furnish me with the concept(s) to study about why light from an object travels differently than one from a source like a star, flashlight, or lightning strike?

It doesn't. What makes you think it does?

 

[dingansich]

It doesn't. What makes you think it does?

this...

Because, in one case, it is relevant, in the other it is not.

If you are not grasping why the rays of light emitted from the surface of the train are not relevant to the experiment, I'm afraid we're going to have a lot of trouble helping you further.

 

[Jimmy Snyder]

Actually from another post a while back, it doesn't actually travel slower, but it will seem to have a slower speed in a medium becausethe photon is absorbed and re-emitted by atoms in that medium.

That sounds suspiciously like a trajectory. I think the path is not mechanical like that.

 

[khemist]

That sounds suspiciously like a trajectory. I think the path is not mechanical like that.

I believe DaveC was the one to post in my thread a while back so he would probably be a better person to elaborate.

Say a photon moves through a dense cloud of gas. From what I understand, the time it takes the photon to traverse through the cloud will be less than the time it would take the photon to travel the same distance, because the photon is constantly being absorbed by the electrons and re-emitted, which takes a finite amount of time. This delay will slow the "speed" of light down, though the velocity it has in between the atoms is c.

 

[dingansich]

It doesn't. What makes you think it does?

or maybe i should have said why is the light from the surface of the train "not relevant?"

 

[DaveC426913]

this...

Perhaps you don't understand what a thought experiment is.

In reality, the light delay is there in all cases. In a thought experiment, we eliminate these realities if
1] they do not help explain the point being made and also
2] if they do not hinder the point in principle.

For example, when doing relativistic rocket thought experiments, we don't worry about how much fuel will be used to get up to .99c, or how long it takes to turn around and fly back home. These are things that, while they are quite real, do not help illustrate the point being made.

It is assumed that the teller and the recipient of the story are able to understand that the thought experiment only needs to address factors that will have an impact on the experiment.


Thought experiments only apply in a carefully limited situation. In your case, the delay of light from source to destination may not hinder the illustration of the point - but if it did - if you could show that it's relevant - then it would indeed have to be accounted for. The thought experiment would have to be modified.