I Alive in one frame and dead relative to other?

[ahmadphy]

I was studying simultaneity and came up with this thought experiment:
Imagine there is a device that when a photon is incident on it it will give electrical shock that can lead to death .
Imagine one person standing on it and one approaching it from left at v and a photon approaching it from the right now relative to the standing person who is touching it the photon arrived and he died but relative to the moving observer since the speed of light is constant and the device is moving to the left the photon didn't arrive yet and hence the standing man is still. Alive . My question is what I had missed here?

 

[.Scott]

You need to consider Lorentz contraction.
For the person on the left, the distance that the photon needs to cross is shorter.

 

[ahmadphy]

Even though both persons wouldn't agree on when the photon arrived am I right?

 

[Dale]

It is hard to know with the description. But most likely you missed the relativity of simultaneity. That is what is missed in most paradoxes. I think in the other frame the photon was emitted earlier.

 

[ahmadphy]

It is hard to know with the description. But most likely you missed the relativity of simultaneity. That is what is missed in most paradoxes. I think in the other frame the photon was emitted earlier.

No in both frames it is emited from the same point simultaneously it's point event I mean the emission and hence relative to all frames the emission is simultaneous

 

[PeroK]

No in both frames it is emited from the same point simultaneously it's point event I mean the emission and hence relative to all frames the emission is simultaneous

The man dies in both frames. Or, to be more precise: the man dies. The coordinates of the time and place of death are different in the two coordinate systems you have implied.

 

[ahmadphy]

The man dies in both frames.

Okay how ? In relativity of simultaneity if there is two devices relative to the rest frame both photons will arrive simultaneously but relative to the moving observer no given that the emission occures at the mid point between the two devices

 

[ahmadphy]

The man dies in both frames. Or, to be more precise: the man dies. The coordinates of the time and place of death are different in the two coordinate systems you have implied.

Then can the moving observer warn the one who is at rest or collide with him before the arrival of the photon relative to the moving frame?

 

[phinds]

relative to the moving observer since the speed of light is constant and the device is moving to the left the photon didn't arrive yet

Yes, it did. When two things (people, photons, whatever) move towards each other, their "closing rate", that is, the speed at which they approach each other, can exceed c even though neither sees the other as moving faster than c. Nothing is moving faster than c in any absolute sense.

Thus, to the moving observer, BOTH the platform AND the photon are moving towards him together and the photon arrives at the platform. To say it another way, the fact that the "moving" observer is moving relative to the platform has no effect on the platform or the photon.

 

[jbriggs444]

No in both frames it is emited from the same point simultaneously it's point event I mean the emission and hence relative to all frames the emission is simultaneous

Yes, there is only one emission event. That event is simultaneous with itself, trivially.

Presumably you mean to ask about the event where the travelling person exists, simultaneously (in the standing person's frame) with the standing person's death. At this event, if we adopt the frame of the standing person, the death is simultaneous. However, if we adopt the frame of the travelling twin, the death event will not be simultaneous.

So what? Either way, the news of the death will be travelling at the speed of light. Either way, the travelling person will not know of the death yet. Eventually the travelling person will get the news. Either way, the elapsed proper time between the starting event we have chosen as above and receipt of the news will be the same.

 

[phinds]

Then can the moving observer warn the one who is at rest or collide with him before the arrival of the photon relative to the moving frame?

Yes, if he is close enough that his signal gets there before the photon, although it's hard to figure how he could know that the photon is on the way since prior to its arrival to him (or to the subsequent signal from the platform after its arrival there) he has no way of knowing of its existence.

 

[ahmadphy]

Yes, it did. When two things (people, photons, whatever) move towards each other, their "closing rate", that is, the speed at which they approach each other, can exceed c even though neither sees the other as moving faster than c. Nothing is moving faster than c in any absolute sense.

Thus, to the moving observer, BOTH the platform AND the photon are moving towards him together and the photon arrives at the platform. To say it another way, the fact that the "moving" observer is moving relative to the platform has no effect on the platform or the photon.

Good I just want to understand more so let me ask this :
We agree that if there is two devices and the emission of two photons were simultaneous at the middle point between them the arrival wouldn't be simultaneous relative to the moving observer right?

 

[jbriggs444]

Good I just want to understand more so let me ask this :
We agree that if there is two devices and the emission of two photons were simultaneous at the middle point between them the arrival wouldn't be simultaneous relative to the moving observer right?

Please review your original post. There are not two devices. There are not two photons. There is only one photon and a shock bomb that detonates unconditionally when the photon arrives. You seem to be discussing a different scenario than the one you actually proposed.

 

[PeroK]

Okay how ?

If the photon hit the device the man was standing on, then the man died from the resulting electric shock. That's called an event. Each coordinate system attributes time and space coordinates to that event. Whether the man dies does not depend on whether you have synchronized clocks.

It's a bit like saying that a man dies in London at 8am GMT and you are in New York, and it's only 3am EST, then you still have 5 hours to save his life.

 

[phinds]

Good I just want to understand more so let me ask this :
We agree that if there is two devices and the emission of two photons were simultaneous at the middle point between them the arrival wouldn't be simultaneous relative to the moving observer right?

Huh? All of a sudden we have TWO photons? I don't see that in your original question.

 

[ahmadphy]

Please review your original post. There are not two devices. There are not two photons. There is only one photon and a shock bomb that detonates unconditionally when the photon arrives. You seem to be discussing a different scenario than the one you actually proposed.

I meant to ask another related question sorry if I confused u

 

[jbriggs444]

I meant to ask another related question sorry if I confused u

That is fine. We can discuss a related question. But first you have to carefully state the new scenario and ask the new question.

We can pretty much guarantee that the resolution will involve the relativity of simultaneity.

 

[ahmadphy]

Huh? All of a sudden we have TWO photons? I don't see that in your original question.

Again I wanted to ask a related question to tell u were I'm confused also read carefully I said I was studying relativity of simultaneity

 

[jbriggs444]

Again I wanted to ask a related question to tell u were I'm confused also read carefully I said I was studying relativity of simultaneity

That is fine. If you want to ask a related question, you should ask it. A question well asked is half answered.

A question poorly asked will generate a plethora of well meaning responses in PF.

 

[PeroK]

A question well asked is half answered.

... and a question asked in terms of coodinates is fully answered!

 

[ahmadphy]

That is fine. If you want to ask a related question, you should ask it. A question well asked is half answered.

Anyhow I wanted to say that if the arrival is simultaneous in the rest frame but not in the moving frame there is an instant were the photon had arrived relative to the rest but not relative to the moving frame in one of the devices am I right? If yes then the standing person is dead in one frame and living in the other

 

[jbriggs444]

Anyhow I wanted to say that if the arrival is simultaneous in the rest frame but not in the moving frame there is an instant were the photon had arrived relative to the rest but not relative to the moving frame in one of the devices am I right? If yes then the standing person is dead in one frame and living in the other

The arrival is either simultaneous in both frames or not simultaneous in either frame.

If it is simultaneous then there is only one event. It is "simultaneous" in every frame.

If it is not simultaneous then there are two arrival events at the same material object. That means that the two events must be time-like separated. They will not be simultaneous in any frame. All frames will agree about the time ordering of the arrival events.

The only event pairs for which simultaneity is frame dependent are event pairs with a space-like separation. All event pairs on the world line of a material object are time-like separated. [Or not separated at all if we are pairing an event with itself]

 

[Dale]

the emission and hence relative to all frames the emission is simultaneous

Simultaneous to what? Your description is too vague.

What makes you believe that they are dead in one frame? What are the distances and times that justify that. Whatever they are, after transforming everything to another frame, everything will be consistent

 

[Dale]

if there is two devices and the emission of two photons were simultaneous at the middle point between them the arrival wouldn't be simultaneous relative to the moving observer right?

Arrival where? It is certainly possible to construct a scenario cleverly arranged such that a pair of light pulses, emitted at the same place and the same time, in opposite directions, reach their respective receivers at the same time according to the moving observer. Your descriptions are too vague

also read carefully I said I was studying relativity of simultaneity

We can read carefully, but the problem is that your descriptions are missing important details. So different people are filling in the blanks differently. You need to eliminate the blanks in the first place.

 

[ahmadphy]

Arrival where? It is certainly possible to construct a scenario cleverly arranged such that a pair of light pulses, emitted at the same place and the same time, in opposite directions, reach their respective receivers at the same time according to the moving observer. Your descriptions are too vague

We can read carefully, but the problem is that your descriptions are missing important details. So different people are filling in the blanks differently. You need to eliminate the blanks in the first place.

Sorry u r right I should have said if they arrive simultaneously relative to rest frame they wouldn't be simultaneous relative to the moving observer

 

[Dale]

Anyhow I wanted to say that if the arrival is simultaneous in the rest frame but not in the moving frame there is an instant were the photon had arrived relative to the rest but not relative to the moving frame in one of the devices am I right? If yes then the standing person is dead in one frame and living in the other

Is this a third scenario? How are you determining in one frame that he is dead? If you properly describe that in one frame, then it is a simple matter of transformation to get a consistent description in another frame. But you have to completely explain how they die (or don’t) in one frame.

Please take a breath and write one scenario clearly and completely, specifying everything necessary in one frame to determine if the person dies.

Sorry u r right I should have said if they arrive simultaneously relative to rest frame they wouldn't be simultaneous relative to the moving observer

Yes.

 

[ahmadphy]

Okay if there is two devices and one observer at rest touching the one on the left and one is too close to him and moving towards him from left to right. he (that who is moving relative to the devices) knows that when he arrive at a specific position two photons at the middle between the devices will be emitted simultaneously relative to all frames because they occured at the same point simultaneously then relative to the moving observer the photon towards the left device will take more time to reach the killing device than relative to the rest observer can he warn the rest observer or collide with hime after he is dead in the rest frame? Because he isn't dead yet relative to the moving person

 

[PeroK]

Okay if there is two devices and one observer at rest touching the one on the left and one is too close to him and moving towards him from left to right. he (that who is moving relative to the devices) knows that when he arrive at a specific position two photons at the middle between the devices will be emitted simultaneously relative to all frames because they occured at the same point simultaneously then relative to the moving observer the photon towards the left device will take more time to reach the killing device than relative to the rest observer can he warn the rest observer or collide with hime after he is dead in the rest frame? Because he isn't dead yet relative to the moving person

Mathematics (in particular kinematics) was invented to avoid this sort of confusion of words. None of this is physics unless you can put some numbers in it and describe quantitatively what is going on.

 

[Dale]

So like this?

Where the observer O is at rest and colocated with detector A. Detector B is some distance away. A flash of light to the left C- and a flash of light to the right C+ are emitted when the moving guy D passes the emitter in between A and B. The flashes C- and C+ arrive at the detectors A and B at the same time in O’s frame.

Do I understand the scenario? If I have misunderstood, please clarify (preferably with a clearly labeled and described diagram). If I have understood, the how do we determine if D dies, what kills D?

 

[martinbn]

At a physics exam one relativity question involves two events, event A and event B. The question asks if the events are simultaneous. The student answers: A is simultaneous, B is not.