# Struggling with the Special Relativity and simultaneity

they will both dispense.
And you (on the cruise ship) will see TWO tweets. A tweet is a notice that the experimental method, suggested by Einstein, proved the simultaneity of the light strikes for the observer that had sent his tweet.

Please tell, what will YOU (on the ship) conclude - DID or NOT the strikes take place simultaneously for EACH of these two observers.

One. The other won't tweet because the flashes of light arrive at different times.
I see the change in your opinion, so please clarify WHICH observer WILL get my drink, and WHICH WILL NOT.

Mister T
Science Advisor
Gold Member
WHICH observer WILL get my drink, and WHICH WILL NOT.
The one on the embankment. Your thought experiment is set up so that only he receives the two flashes at the same time.

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Mister T
Science Advisor
Gold Member
No, the light pulses expand as circles in both frames as is required by the invariant speed of light.
Yes, they do. But the thing that's a circle in one frame is not a circle in the other.

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Nugatory
Mentor
And you (on the cruise ship) will see TWO tweets. A tweet is a notice that the experimental method, suggested by Einstein, proved the simultaneity of the light strikes for the observer that had sent his tweet.
Here we're discussing the case in which both dispensers are at the same place at the exact moment that the two flashes of light arrive at that same place, so both dispensers dispense a beer and two tweets are sent. (Note that I am only able to say "the exact moment" because we're talking about a single point in space).

In this case only one of the two observers will satisfy the other requirement of Einstein's procedure, namely that both light flashes travelled the same distance from point of emission to point of detection so were in flight for the same amount of time. Therefore only one of the two observers will find the emission events to be simultaneous.

Please tell, what will YOU (on the ship) conclude - DID or NOT the strikes take place simultaneously for EACH of these two observers.
The strikes were simultaneous for whichever observer calculates that the both of flashes of light spent the same amount of time in flight. This will be the observer for whom the distance between the strike point and the position of his detector when the strike happens is the same for both strikes. Because the detectors are moving relative to one another, you cannot arrange things so that they are both in the same place when the two light flashes arrive and that they are both the same distance from the strike points when the strikes happen - you can make it that way for one of the observers but not both.

OK. I think then that I'm satisfied. Simultaneous is simultaneous, and nobody is really saying otherwise. Thanks all.

Mister T
Science Advisor
Gold Member
Please tell, what will YOU (on the ship) conclude - DID or NOT the strikes take place simultaneously for EACH of these two observers.
Are you talking about the lightning strikes or the flashes arriving at the dispenser? You can arrange things so that the flashes arrive at both dispensers at the same time, but then the lightning strikes can be simultaneous for only one observer. In that scenario both dispensers have the same location when the flashes arrive, and they both dispense a beer.

But that's not the way it's presented in the book by Einstein that you referred us to, and it's not the way you originally presented it to us in your beer dispenser scenario.

The way you presented it the flashes arrive at one dispenser simultaneously and it dispenses a beer. The strikes are simultaneous in that dispenser's frame. Later one flash arrives at the other dispenser, and then later the other flash arrives.

The central issue is this. The strikes occur at different locations. The dispenser occupies one location.

If events are separated in space and occur at the same time in one frame, such as two lightning strikes, they might not occur at the same time in another frame of reference.

If events are not separated in space and occur at the same time in one frame, such as the arrival of the flashes at a dispenser, they must occur at the same time in all frames.

The one on the embankment. Your thought experiment is set up so that only he receives the two flashes at the same time.

Once again MANY THANKS to ALL posters for the very informative, thoughtful and helpful discussion.

A train was moving with a constant speed along the very straight tracks when two lightnings perforated it vertically in two different places, leaving unmistakable holes under the train in the ground between the railways.

Mik was cringing in a dunk earth pit between the tracks somewhere in-between the holes made by the lightnings in the GROUND, the sensors of his dispenser sticking out. Mit1 was enjoying life in a first class train compartment somewhere in-between the holes made by lightning strikes in the TRAIN, his dispenser on a velvet carpet nearby.

Mik and Mit1 both knew that their dispensers will drop beer bottles if and only if two light rays, coming from opposite directions, both touch a dispenser at exactly the same time. They have read also that a panel of philanthropists on a cruise ship is watching our discussion and will give a free iPhone 6s Plus 128GB (Rose Gold) to who of them will tweet an undisputable proof that he had determined FROM HIS SURROUNDING (aka reference system – train or ground respectively) that the two thunderstorm lightnings in question took place simultaneously.

As it happened the Mik’s dispenser did drop a bottle and as soon as the train had passed Mik climbed out of the pit and hurried to measure (along the straight line connecting the holes), with HIS rigid measuring rod, the distances from HIS dispenser sensors to each of the holes made by the lightnings in the GROUND. Hurrah! he cried, as both these distances were exactly the same, and tweeted joyously:

My dispenser, positioned on the GROUND exactly in-between the lightning holes in the GROUND (as measured along the GROUND), dropped a bottle and therefore the two light signals that contacted my dispenser at the same time had travelled (from the lightnings to the dispenser) exactly the same time which means that these signals were generated by lightnings at the same time, which is the proof that AS DETERMINED ON THE GROUND the two lightnings DID happen SIMULTANEOUSLY.

Mit1 also determined (with HIS rigid measuring rod) INSIDE the MOVING TRAIN that the distances from the two MOVING holes (in the TRAIN) along the MOVING straight line towards the sensors of HIS dispenser (which was MOVING with the TRAIN’s velvet support) are exactly equal and tweeted cheerfully in almost the same words as Mik (instead of GROUND there were the words TRAIN) that he has HIS proof that AS DETERMINED FROM THE TRAIN the lightnings DID happen SIMULTANEOUSLY.

Both Mik and Mit1 looked forward in high spirits to a FedEx personal parcel with the Apple iPhone, but as it happened only Mik did actually receive it.

Philanthropists found Mit1’s description of the events on the train and his tweet, that he has proved FROM THE TRAIN that the lightnings struck the TRAIN simultaneously, implausible as being just a copycat of the Mik’s indubitable facts and proof, which were stolen from Mik by Chinese hackers.

To add insult to injury Mik for his part has tweeted that ONLY his proof of simultaneity is true and that he DISAGREES with the Mit1’s claim on the Apple as HE Mik had OBSERVED personally that the Mit1’s dispenser on the train was speeding TOWARD one and AWAY from another of the two places where HE Mik had found the lightning footprints in the GROUND, and that HE Mik CONSIDERS this observation as an unquestionable evidence that the Mit1’s dispenser SHOULD have stumbled into the light signal from the TRAIN’s front hole before the signal from the rear hole COULD have caught with this dispenser.

While Mik was enjoying the free Apple (for his successful proof of the lightnings’ simultaneity as determined on the Ground), Mit1 was beside himself and suspecting the role played by his gender, race, religion, skin color, sexual orientation, marital status, birth of place, citizenship, party affiliation, etc., Mit1 decided to fight for his constitutional rights to have the Apple also, and he tweeted again:

I will claim my free Apple in the Court with the following factual evidence:

A) This was an elite train that was MOVING so quiet, soft and UNIFORM that the passengers felt as if it was still staying put.

B) A written statement from Prof. Einstein: “People travelling in this train will with advantage use the train as a rigid reference body (co-ordinate system); they regard all events in reference to the train”

C) The bottle dropping testifies that the two light signals have reached the dispenser on the TRAIN at the same exact time. The dropping was witnessed by a high ranking traveler (on her election campaign trip), and in case she is suspected of lying the dropping is recorded in the dispenser’s hardware.

D) The distances ALONG THE TRAIN from the dispenser to the FRONT and the REAR places on the TRAIN where the lightnings struck the TRAIN were exactly equal.

According to Prof. Einstein’s statement it is LEGITIMATE TO MEASURE INSIDE AND ALONG THE MOVING TRAIN THE DISTANCES which the light rays, that have brought to the TRAIN dispenser the information about the lightnings piercing the TRAIN, had travelled. This statement gives a strong support to the validity and preeminence of my proof against the critique and considerations presented by Mit.

Because these DISTANCES were measured as EXACTLY THE SAME and these RAYS TOUCHED THE DISPENSER AT EXACTLY THE SAME MOMENT these information rays had TRAVELLED (along the MOVING TRAIN) EXACTLY THE SAME TIME and therefore ORIGINATED (at the points where the lightnigs struck the train) AT THE SAME TIME, and that therefore the lightnings DID happen and strike the train SIMUTANEOUSLY.

I will petition the Court to give preference (against the Mik’s rejection, by CONTEMPLATION) to My FACTS and MEASAUREMENTS based proof, so that I also get a free Apple for the lightnings SIMULTANEITY determined by me Mit1 FROM THE MOVING TRAIN as undeniable as their SIMULTANEITY was determined by Mik FROM THE GROUND.

Mister T
Science Advisor
Gold Member
Mit1 also determined (with HIS rigid measuring rod) INSIDE the MOVING TRAIN that the distances from the two MOVING holes (in the TRAIN) along the MOVING straight line towards the sensors of HIS dispenser (which was MOVING with the TRAIN’s velvet support) are exactly equal and tweeted cheerfully in almost the same words as Mik (instead of GROUND there were the words TRAIN) that he has HIS proof that AS DETERMINED FROM THE TRAIN the lightnings DID happen SIMULTANEOUSLY.
Being equidistant from the two events is not proof that the events were simultaneous. Mit1's dispenser wouldn't have dispensed because a flash of light sent from one of the strikes would have arrived before the other. (The one in front would have reached him first because he was traveling towards it.) Since he was equidistant from the events he now has proof that the events were not simultaneous!

Janus
Staff Emeritus
Science Advisor
Gold Member
Once again MANY THANKS to ALL posters for the very informative, thoughtful and helpful discussion.

A train was moving with a constant speed along the very straight tracks when two lightnings perforated it vertically in two different places, leaving unmistakable holes under the train in the ground between the railways.

Mik was cringing in a dunk earth pit between the tracks somewhere in-between the holes made by the lightnings in the GROUND, the sensors of his dispenser sticking out. Mit1 was enjoying life in a first class train compartment somewhere in-between the holes made by lightning strikes in the TRAIN, his dispenser on a velvet carpet nearby.

Mik and Mit1 both knew that their dispensers will drop beer bottles if and only if two light rays, coming from opposite directions, both touch a dispenser at exactly the same time. They have read also that a panel of philanthropists on a cruise ship is watching our discussion and will give a free iPhone 6s Plus 128GB (Rose Gold) to who of them will tweet an undisputable proof that he had determined FROM HIS SURROUNDING (aka reference system – train or ground respectively) that the two thunderstorm lightnings in question took place simultaneously.

As it happened the Mik’s dispenser did drop a bottle and as soon as the train had passed Mik climbed out of the pit and hurried to measure (along the straight line connecting the holes), with HIS rigid measuring rod, the distances from HIS dispenser sensors to each of the holes made by the lightnings in the GROUND. Hurrah! he cried, as both these distances were exactly the same, and tweeted joyously:

My dispenser, positioned on the GROUND exactly in-between the lightning holes in the GROUND (as measured along the GROUND), dropped a bottle and therefore the two light signals that contacted my dispenser at the same time had travelled (from the lightnings to the dispenser) exactly the same time which means that these signals were generated by lightnings at the same time, which is the proof that AS DETERMINED ON THE GROUND the two lightnings DID happen SIMULTANEOUSLY.

Mit1 also determined (with HIS rigid measuring rod) INSIDE the MOVING TRAIN that the distances from the two MOVING holes (in the TRAIN) along the MOVING straight line towards the sensors of HIS dispenser (which was MOVING with the TRAIN’s velvet support) are exactly equal and tweeted cheerfully in almost the same words as Mik (instead of GROUND there were the words TRAIN) that he has HIS proof that AS DETERMINED FROM THE TRAIN the lightnings DID happen SIMULTANEOUSLY.
There is only one point on the train where the light flashes arrive simultaneously, and that is the point that is adjacent to To the point where the lights meet on the ground ( halfway between the holes in the ground). This point will not be halfway between the holes on the train. Everyone, no matter where they are or how they are moving will agree to this. Mik agrees to this, Mit1 agrees to this, you agrees to this, and everyone on the cruise ship agrees to this. Thus everyone agrees as to who's dispenser was triggered. The fact the Mit1 measures the distance to each hole in the train as being the same also means that he will say that the strikes took place at different times because he will not see the two flashes at the same time.

It is exactly because you cannot have a situation where one person says his dispenser gave him a bottle and the other didn't, while someone else says the opposite that leads one person to conclude that the lightning strikes occurred simultaneously and the other to conclude that they did not.

PeterDonis
Mentor
2019 Award
The OP's question has been answered, multiple times. Thread closed.

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