0 Members and 1 Guest are viewing this topic.

An actual measurement, as described, also predicted by (and assuming) that interpretation.

She going about that task all wrong then. She's doing this funny procedure with some clocks and light equipment. At no point is she instructed to perform some kind of test that would distinguish between one kind of universe and another. She's in the wrong thought experiment.If that's her task, why do we have her doing this unrelated procedure?

If the experiment weren't to unfold in the way the thought experiment does then both interpretations would be wrong, since both interpretations predict the same observations for Alice.

What observation are you talking about? You didn't describe any such observation.

If it made such a prediction, the description would not be open to interpretation. So this is nonsense. There have been attempts at doing just that, whenever the test comes up positive for the relative interpretation, the test is declared invalid rather than being declared actual falsification of said alternate interpretation. Translation: the testers commit selection bias.

It does, but so does yours. That's the nature of any interpretation of something. The circularity is necessary. Self consistency means there are no contradictions along the circle.The two interpretations have differing definitions of simultaneity, so each must assume its own definition when describing simultaneous events. That's the circular conclusion that must be employed. But the differing definitions are not premises, but rather necessities that follow from the premises. So in that sense, neither interpretation is circular.

No claim of simultaneity was made. Alice tested that the clocks are simultaneous in this one frame (the ship in the latest description). That test relied on the interpretation of choice, yes. She performed no test to attempt a falsification of one interpretation or the other. Nobody in the thought experiment attempted to do an absolute sync of the two clocks. If they desired to do so, the procedure they're using is completely wrong.

Well Alice didn't conclude that. She performed a frame dependent test that makes syntactic sense only in the one interpretation. If it makes you feel better, she demonstrated (in the absence of interpretation assumptions) that C1 and C2 appear simultaneous in that frame and wrote off the issue of their being actually simultaneous or not as having no practical significance, only philosophical significance. She'd be right about that.

There are no specific events which are being assumed simultaneous. It (the whole thing, not the bolded part) is a statement of RoS which can be applied to events already found to be (not assumed to be) simultaneous in a frame.

The bolded part makes no assertions. It is effectively a conditional phrase: "If two events are simultaneous in some frame". It is not assuming any specific events are in fact simultaneous since no events are identified. The meaning of 'simultaneous in a frame' is already established at the time such a statement would be made.

The statement above is not one concluding RoS. It is stating (not concluding) that two such events meeting the qualification in bold part might also meet the qualification in the underlined part. It uses the already established (not assumed) RoS to do this.

I never said any conclusion was assumed. All were derived. It is circular in that it assumes (never proves) its own premises. It results in a relative definition of 'simultaneous', but that again is derived, not assumed.

Alice is performing a relative procedure (assuming a relative interpretation) and concluding that two events are simultaneous in a way meaningful only to that interpretation. That's the circularity of it that I'm talking about.

For the record, SR theory proper does not assert constant light speed. It only presumes the frame independent appearance of it. It is the relative interpretation of SR theory that makes the metaphysical assumption that said light speed actually is constant. This metaphysical interpretation is probably the most mainstream interpretation, but being metaphysics, lacks any kind of evidence to support it. Einstein himself very much used the relative interpretation.That said, in making that statement above, you burden yourself with an assumption that there is a stationary system. If we're going to drop the metaphysical assumption that light speed is (not just appears) constant in any frame, we also need to drop the stationary frame concept. Not doing so would be 'circular reasoning' the way you seem to use the term.So we drop all these assumptions. Now what? In the absence of such assumptions, where do we go?

They had a convention. This is pre-relativity, so they used Earth frame without knowing that it mattered. They were (in hindsight) measuring the speed of light as it appeared in that frame. It wasn't until considerably later that measurements became accurate enough to conclude the frame independence of that appearance.You put a clock far away and observe it from a distance. When it appears to read zero, you zero the local clock. That's the sync convention that was used. The two clocks, unchanged, should always locally appear to read the same value.I’m presuming you can see how this means that the two clocks aren’t actually synced.If light speed was infinite, then the local clock would always be in sync with the observed value on the distant clock (and in fact would be the actual value). If light speed is some finite number, then changing the distance between the observer and the distant clock should (and did) change the sync between the two clocks. The distant one would appear to log less time (run slower) as it moved further away and more time was needed for light to get from there one-way to the observer. It would appear to get ahead as the distant clock grew closer.By observing this change in the sync between the two clocks, a remarkably accurate measurement of one-way light speed was taken.....The people back then used a different convention, but one just as valid. In particular, it didn't rely on two-way light trips. There were no mirrors involved.

You and I have quite a different definition of what a prediction is. I have an empirical definition, not a metaphysical one.

How is the premise a conclusion? It's just a tautology. Assuming that I have 5 apples, then I have 5 apples. Yes, that's circular, but not invalid. I don't consider my having 5 apples to be a conclusion, but rather the premise. RoS on the other hand is not a premise.

Don't know what you mean by this. The first part seems to suggest that simultaneity is meaningless. The second part seems to suggest a different metaphysical assumption, and you seem to balk at such assumptions, labeling any conclusions drawn from them to be circular and thus somehow fallacious.

We were talking about testing C0, so it would be light from A and B1 that must travel to the camera. We've already done the procedure for B1 and B2. You introduced this 3rd clock and asked how to verify how much it is out of sync with the other two.

You said you accepted the interpretation as valid. Now you say otherwise.

So you assert, but this evidence is never presented. So this is an empty assertion. Please don't make statements like this without referencing at least one piece of evidence that contradicts what the interpretation says should be observed. I don't make this statement about your pet interpretation despite my thinking that it has metaphysical issues.

Where did I say that? I assumed an actual constant relative speed of light. I cannot prove that it doesn't just appear to be that way. I made no more assumptions than that. I did not conclude from that assumption that those events were simultaneous.

I didn't claim that. You are putting a lot of words in my mouth. How many times must I point out claims that I didn't make? The signals returning simultaneously to the detector verify that C1 and C2 are in sync in that frame, and do not constitute any sort of verification concerning C0.I also said that the reading on the C0 clock at the time did not play any role in the verification of what Alice is attempting to do with C1 and C2.

To be picky: B1 and B2 are locations, and one cannot make physical contact with a location.That was probably a typo. You mean physical contact with the clocks C1 and C2 bolted there.

Yes to all that, but none of that describes a verification procedure for it.

Did Einstein put a 3rd clock between the two in his description of the convention to sync the first two? Don't remember that.

I will not agree to that. I've said repeatedly that SoR does not assume SoR. It follows from different premises. I agreed that those different premises cannot be proved.

As such, it is an untestable/unfalsifiable prediction/conclusion/hypothesis however you want to frame it.

Quote Alice is simply performing an experiment to try and help her determine what kind of universe she/we lives in. From her plausibly actualised observations we can draw conclusions about the universe thst we live in.How so? What has Alice ever done that might make you conclude one way or the other?

Alice is simply performing an experiment to try and help her determine what kind of universe she/we lives in. From her plausibly actualised observations we can draw conclusions about the universe thst we live in.

No, it requires the premises leading to that conclusion to be assumed. Nobody ever assumed RoS. They assumed something else. That something else is what we need to drop if we wish to determine what sort of universe we live in (A or R). To not drop that assumption would indeed be begging a conclusion, even if RoS isn't the assumption being dropped.

Wrong. That conclusion also requires you to assume that it isn't relative, not just drop the assumption that it is relative. You've made a different assumption if you don't do that.It is the difference between "I don't know" and "I know R is wrong". Only under the latter assumption allows the conclusion you make above. You are otherwise assuming the conclusion.If you want to make a determination between the two, start with "I don't know".

QuoteIt simply requires us to consider the totality of empirical evidence only and not append any assumptions to that evidence; assumptions that are contradicted by the evidence.I agree you need to do that, but it is not enough. It requires more than that. It in fact requires a falsificaton test, and lacking that, the two views remain just interpretations.

It simply requires us to consider the totality of empirical evidence only and not append any assumptions to that evidence; assumptions that are contradicted by the evidence.

My apologies, I may have overstated the case.She is performing a procedure from which deductions and inferences can be drawn and applied to the different interpretations.

Quote from: HalcIf the experiment weren't to unfold in the way the thought experiment does then both interpretations would be wrong, since both interpretations predict the same observations for Alice.Agreed, which is why we can treat it as though it has actually happened and draw inferences and deductions from it.

The mathematics are the same for the different interpretations.

As such, they make truth claims about the configuration of a system.That is, predictions about the configuration of the system can be extracted from the different interpretations.

Truth claims are not predictions since there is no way to directly verify them.

From the Einsteinian interpretation we can extract a prediction about the configuration of the physical system which says the reading on clock A will be d/c for events B1 and B2 i.e. events B1 and B2 will be simultaneous with the reading d/c on C0 – this statement about the physical system can be extracted from the interpretation.

The position being advanced is that the Simultaneity of events in the stationary system cannot be determined – this fact is derived from the observational evidence, not from an assumption, so it is not circular.

This is the crux of the issue! How are the events “found to be (not assumed)” simultaneous in the frame i.e. what observation does Alice make that confirms that events B1 an B2 are simultaneous meaning that the clocks are sychronised.

What observation does she make that confirms that the demands of the mathematics are fulfilled?

The Einsteinian interpretation says simultaneity is relative.

IF events are not assumed to be simultaneous, the conclusion that simultaneity is relative cannot be reached.

The question as to what empirical observation can be made to determine that two such events are simultaneous in the physical configuration of the system remains.

You are confusing the idea of deriving something mathematically and deriving something from observation.

The simultaneity of the events that is derived from the mathematics is a prediction. Just as the statement about the configuration of the system - where events B1 and B2 coincide with the reading d/c on C0 - derived from the Einsteinian interpretation, is a prediction (as you’ve stated above).

It certainly isn’t derived from observation. The accuracy of the statement – about the physical configuration of the system – made derived from the Einsteinian interpretation must be assumed because it certainly is not observed, in any empirical manner.

Just to be clear, the alternative interpretation says that the simultaneity of events cannot be determined in the stationary system and so does not rely on circular logic.

Quote from: HalcAlice is performing a relative procedure (assuming a relative interpretation) and concluding that two events are simultaneous in a way meaningful only to that interpretation. That's the circularity of it that I'm talking about.It is also the circularity I am talking about. Alice is performing a valid variation on the prescribed synchronisation procedure. As such, inferences and conclusions can be drawn from it. She “[concludes] that [the events] are simultaneous in a way meaningful only to that interpretation. Let’s think about that statement. How is it meaningful to that interpretation? All other observers say the events weren’t simultaneous.

Alice must conclude that events in her frame are simultaneous for this interpretation to be valid.

How does she conclude that the events are simultaneous? Not by way of empirical observation – the theory itself precludes it.

Empiricism requires that mathematical predictions/calculations be verified by empirical observations (hence the name empiricism). How then does she conclude that the events were simultaneous in such a way that it is meaningful to the interpretation?

[An assumption must be made that] events are simultaneous in her frame – bcos we already have the observational evidence to the contrary

Quote from: HalcSo we drop all these assumptions. Now what? In the absence of such assumptions, where do we go?We can simply say that the average [of the two-way] speed of light is c.

So we drop all these assumptions. Now what? In the absence of such assumptions, where do we go?

Or just not make any assumptions about the simultaneity of events.

Either way, we can draw inferences and deductions from the thought experiment, as is.

Sounds very interesting. Can you recommend a source that shows the peer review of this confirming that it measures the one-way speed of light.

I and many others would be very interested in reading it. Until then, I’ll go with the peer reviewed stuff that says it hasn’t been successfully measured.

It is interesting though that you are offering something which measures a different value for the speed off light (close though it may be) and asserting that this different value demonstrates that the one way speed of light is constant.

Quote from: Halc on 14/06/2019 15:22:46 You and I have quite a different definition of what a prediction is. I have an empirical definition, not a metaphysical one.A statement about the configuration of the physical system can be derived from the Einsteinian interpretation. This represents a prediction.

It is a statement upon which one of its core conclusions rests entirely. It is a statement whose accuracy must be assumed; therefore one of its core conclusions must be assumed.

A more accurate analogy:If 5 pieces of fruit are apples in one frame, then they are oranges in a relatively moving frame. The observer in the stationary frame cannot see the pieces of fruit – under the foundational assumptions of the interpretation (a glass box with a non-transparent lid, where they can only look down on the box. All relatively moving observers make empirical observations (seeing into the box from the side) that the pieces of fruit in the box are oranges. The observer assumes that the 5 pieces of fruit are apples, therefore fruit is frame dependent.

We’re checking to see if the reading d/c on C0 coincides with events B1 and B2 i.e. testing to see if B1 and B2 are acctually synchronised in the stationary system

Quote from: Halc You said you accepted the interpretation as valid. Now you say otherwise.My apologies, I probably intended to say that it was self-consistent.

It’s validity is dependent on whether an interpretation that assumes its conclusions is more valid than one that doesn’t.

Quote from: HalcPlease don't make statements like this without referencing at least one piece of evidence that contradicts what the interpretation says should be observed.The empirical evidence is that which can be deduced from the thought experiment – which represents a plausible real world experimental set-up, from which we can draw inferences and conclusions – the empirical observations of all other observers.While it doesn’t contradict the interpretation, it contradicts the assumption upon which the interpretation hangs.

Please don't make statements like this without referencing at least one piece of evidence that contradicts what the interpretation says should be observed.

The interpretation represents a map. The plausible real world set-up [as represented by the thought experiment] represents the territory. On the map there is a lake called Loch Ness. “In” the lake there is a picture of a partially submerged creature labelled “the Loch Ness Monster”. The key on the side of the map says that the Locch Ness Monsters presence in the lake must be “established by definition” i.e. it must be assumed that Nessy be in them there waters. The territory might look a lot like the map, but the underwater footage of the lake with no sign of Nessy certainly contradicts the assumption.

There is no empirical observation [that can be made] to verify the prediction/statement of the physical system than can be derived from the Einsteinian interpretation.

There is no empirical observation which supports the contention that the clocks on Alice’s spaceship are synchronised, all empirical evidence shows the clocks on the spaceship are not synchronised.

The contention that the clocks on board the spaceship are synchronised (from anyone’s perspective) is not supported by empirical observation so it can only be assumed.

The signals returning simultaneously to the detector verify that C1 and C2 are in sync in that frame. No they don’t! They verify that the signals return simultaneously to the detector. As has been pointed out, the signals would return simultaneously if the time to C1 and C2 were not the same, as this would be evened out on the return leg.

As you quite rightly state it does not “constitute any sort of verification concerning C0”, as such verification is impossible.

Ask yourself, how then can Alice be sure that her calculations (which rest on her assumption) are actually correct, in her frame?

How does Alice determine that the clocks are synchronised if it isn’t by way of observation that both events happen “at the same time”. How does she determine that the “demands” made by her mathematics are met by the physical system?

It might be worth pointing out now, too, that her conclusion of length contraction also rests on the assumption that her clocks are synchronised.

Given that both clocks remain bolted to their respective spots means that for the purposes of what we are discussing – Alice’s synchronisation procedure in her spaceship – the distinction between points and clocks are immaterial because they remain co-located.

See what I mean about having difficulty with seeing how the thought experiment represents a valid variation on Einstein’s synchronisation procedure. That is why C0 – the name you gave it – was introduced. In Einstein’s convention he has light going from [the clocks at]:A > B > A

In our thought experiment we have light going from the clocks at:A > B1 > AA > B2 > A

Can you now see how it is a valid variation on Einstein’s convention?

Incidentally, I don’t remember Einstein mentioning anything about flying 2 atomic clocks around the world on commercial airliners, but this represents a test of his theory because the prediction can be derived/extracted from the interpretation. Just as the statement/prediction pertaining to the reading on C0 can be derived/extracted.

Quote from: Halc I've said repeatedly that SoR does not assume SoR. It follows from different premises.If there is no empirical observation that the clocks in Alice’s spaceship are synchronised with each other, in her frame of reference

I've said repeatedly that SoR does not assume SoR. It follows from different premises.

Given that the conclusion of RoS hangs by a string on the idea that the clocks are synchronised

Quote from: HalcWhat has Alice ever done that might make you conclude one way or the other?Alice has demonstrated that the idea, that her clocks are synchronised in her frame, is not supported by any empirical evidence so it must therefore be assumed.

What has Alice ever done that might make you conclude one way or the other?

Quote from: Halc If you want to make a determination between the two, start with "I don't know".The alternative doesn’t rely on circular reasoning because it makes no statement about the simultaneity of events in the stationary system.

If you want to make a determination between the two, start with "I don't know".

It simply says that this cannot be determined

If we consider Alice’s assumption:The clocks on Alice’s spaceship are synchronised with each other.

What empirical evidence is there to support that assumption? There is no actual evidence to support it.

Synchronization of separated clocks cannot be observed.

QuoteYou are confusing the idea of deriving something mathematically and deriving something from observation.No I'm not. It's all quite mathematical since we're discussing synchronization, something that only has abstract meaning.

Again, we have to bring things right back to basics before we can proceed any further, and I believe this is the sticking point.Quote from: HalcSynchronization of separated clocks cannot be observed.This is exactly the point! If Alice cannot observe that the clocks in her inertial frame are synchronised

Quote from: HalcQuoteYou are confusing the idea of deriving something mathematically and deriving something from observation.No I'm not. It's all quite mathematical since we're discussing synchronization, something that only has abstract meaning.The synchronisation procedure is a real-world, physical process. It is not simply a mathematical procedure.

Yes, mathematics are abstract and the definition of synchronisation under a mathematical co-ordinate frame is an abstraction

but there's a reason why empirical tests are required to verify mathematical predictions. To check the validity of the abstract mathematics.

The abstract mathematics doesn't necessarily imply that the clocks are synchronised.

The Lorentz-Poincare interpretation also employs the Lorentz transformation between the relatively moving reference frames, but the clocks in those reference frames are not synchronised, under that interpretation.

So, from the abstract, mathematical, stationary, co-ordinate reference frame that Alice chooses to employ

we can derive a prediction about the [real-world, physical, not-mathematical] clock synchrnoisation procedure that Alice carries out onboard her physical, not mathematical spaceship, which constitutes her "stationary system". This mathematical description says that the reading on the [real-world, physical, not-mathematical] clock, which we have labelled as "A", that the reading on this clock that corresponds to the [real-world, physical, not-mathematical] photon making physical - not mathematical - contact with the [real-world, physical, not-mathematical] clocks [which we have labelled] B1 and B2 (because they are nailed to the floor at points B1 and B2, in her "stationary system"/in her reference frame), that the reading on this clock will correspond to a value of d/c and will be the same for both [real-world, physical, not-mathematical] events.

If she cannot observe it then she can only assume it, she can only establish it by definition.

Hey roosh, how was the trip?

I didn't say 'in her inertial frame'.

Given an abstract selection of a coordinate system, the synchronization of two clocks can very much be measured/observed, per Einstein's definition of synchronized clocks. That procedure even works in your interpretation.You send a pulse at time T1a from a clock at one location and measure the time T1b on the clock at the distant location when that pulse is received. Subtracting the two gives duration D1. You do the same in the reverse direction to get D2. Iff D1 and D2 are equal, the clocks at those two locations are in sync in the selected frame by definition.

Since the frame selection is an arbitrary selection of abstract coordinate systems, the statement that two clocks are in sync in that frame is a purely abstract statement. Perhaps your disconnect is along those lines, like Alice is making some sort of metaphysical claim when she runs her verification procedure. She's not.

QuoteYes, mathematics are abstract and the definition of synchronisation under a mathematical co-ordinate frame is an abstractionBut that abstraction is all that Alice is claiming.

Disagree. I can think of no physical procedure that is used to verify a purely mathematical concept. One can verify the preduction that a sync procedure (done from the midpoint say) indeed produces a valid sync by doing the verification by definition (which is not done at the midpoint), but that i8 a test that the physical behavior matches the mathematical model, not a verification of the mathematical definition.

QuoteThe abstract mathematics doesn't necessarily imply that the clocks are synchronised.No frame reference, so I don't disagree with this.QuoteThe Lorentz-Poincare interpretation also employs the Lorentz transformation between the relatively moving reference frames, but the clocks in those reference frames are not synchronised, under that interpretation.By definition, yes. Still not disagreeing.

It isn't stationary. It is an arbitrary frame. The fact that you found one mention of the word 'stationary' as a simple designation in Einstein's work is not an assertion that the frame is a preferred one. I continue to harp on this because you're using the concept to give metaphysical meaning to something that isn't a metaphysical statement.

I didn't get the last bit: "will be the same for both events". What events? I assume the zeroing events of the clocks at B1 and B2, in which case I agree that the reading of d/c on clock at A would be simultaneous with those two zeroing events in the frame where all the clocks involved remain at their respective locations.

Establishing it by definition is not assuming it.

She's quite capable of applying the definition and verifying it. She has not done so in the procedure you describe above. The definition doesn't involve a 3rd location.

Quote from: HalcI didn't say 'in her inertial frame'.This is probably a big part of the issue. I am trying to clarify my thinking but I am using terms imprecisely/interchangably, which is probably leading to us talking past each other in some cases. I'm having a similar discussion on another forum with people who I'e debated against before, who are probably used to me doing this, so haven't been pulling me up on it, because they understand the point I am trying to make. So, I haven't learned to be more precise. So apologies if that is the case.

Apologies, can we walk thru this bcos I'm not fully clear on your reasoning here. I'll outline my understanding, sticking as closely to the Einsteinian synchronisation procedure as I can, and you can highlight where I'm going wrong - if that suits?

You have the 2 clocks as you outline there. Let's call the clocks C1 and C2 for convenience. At time T0 on C1, you send the pulse to C2, which zeros C2. How do you measure the duration of the journey from C1 to C2?

or, do you mean:that both clocks are started independently, not synchronously and at the random time T1a [on C1], a pulse is sent from one clock to the other clock [C2] which registers the time of T1b. Subtract the 2 values to get D1. This would give us a random value not necessarily the duration of the journey from C1 to C2 - because we don't know if the clocks were started simultaneously. Lets, for arguments sake, say that the value it gives us is 2 units of time.

Then, at a random time T2b a pulse is sent from C2 to C1. The 2 values are subtracted to give D2. Let's imagine for a second though, that C2 was started 1 unit of time before C1. Subtracting the two values will give us 0 (assuming the same journey time).

This is where the disconnect is, I think. We don't need to assume that she is making a metaphysical claim - even though such a claim has pretty drastic metaphysical implications pertaining the the physical structure of the universe, stemming from that claim.

We need only talk about the physical system in which Alice finds herself, and the physical synchronisation procedure that she carries out. We're talking about empirical verification of Alice's claims. In this sense, her statement that the two clocks are in sync is not a purely abstract statement. It's a statement about the physical configuration of a real-world inertial system.

Quote from: HalcBut that abstraction is all that Alice is claiming.And what we're doing is seeing how well Alice's abstraction maps onto the physical world. We're checking to see if her abstraction can be verified empirically.Given Alice's abstraction we are free to derive/deduce other claims about the configuration of her physical system that follow as a necessity from her abstraction. Alice may not have expreessly stated these from the outset, as she may have been unaware of them, but as with any physicl theory/interpretation, we can see what it logically necessitates and go about testing that, empirically. In doing so, we can see that her abstraction includes a logically necessary statement about the simultaneity of clock synchronisation events and their coincidence with the reading on a clock located midway between them. This is simply a statement about the configuration of the physical system that we can deduce from Alice's abstraction and which gives us further insight into her interpretation.

But that abstraction is all that Alice is claiming.

As we have agreed, this part of Alice's abstraction cannot be verified empirically, that is, we cannot determine, by way of observation, that Alice's abstraction is an accurate representatation of the physical world.

For Alice to maintain her belief in this abstraction she does so, not on the basis of empirical observation, she does so only by way of assumption.

In this sense, Alice's abstraction (co-ordinate reference frame) is the "map" and her physical, inertial frame is the territory.

As has been stated, we can derive a statement from Alice's abstraction about the physical configuration of her inertial frame i.e. her physical, "stationary system".

This claim pertains to the reading on the clock at the midpoint. It is a logically necessary statement about the physical system, derived from her abstraction. As a statement about the configuration of a physical sysyem, it is subject to the rules of empiricism. Empirically speaking it is untestable. So, from a purely empiricial standpoint, it is an assumption.

The Lorentz transformation does not necessitate that simultaneity is relative because there are [at least] 2 difffering interpretations of the evidence which employ the LT.

One interpretation concludes the relativity of simultaneity, the other doesn't, so RoS is not a necessity of the Lorentz Transformation.

Quote from: HalcI didn't get the last bit: "will be the same for both events". What events? I assume the zeroing events of the clocks at B1 and B2, in which case I agree that the reading of d/c on clock at A would be simultaneous with those two zeroing events in the frame where all the clocks involved remain at their respective locations.This is precisely what I meant. This is the statement about the configuration of the physical system that can be derived from Alice's abstraction.

It is this that cannot be observed and which must be assumed. If either of the zeroing events is not simultaneous with this reading, then the two clocks are not synchronised. Alice has no way of verifying, empirically, that the zeroing events are simultaneous with this clock reading . Therefore, from an empirical standdpoint, she can only assume that this is the case.

Maybe not. However, it is the not being able to verify it empirically that makes it an assumption.

OK. The synchronization procedure is not the same as the verification-by-definition procedure... just so you know. The former is how one goes about syncing the clocks in a frame, and the latter is one way to verify that they're indeed in sync in that frame.

The verification procedure (the 'by definition' one) doesn't zero anything. When clock at C1 reads T1, it sends the pulse, which is received at C2 at T2 say. The duration is T2-T1 as measured by those respective clocks. That's the number we're after. It might be negative, but the clocks are not in sync if it is negative.

There is a critical issue with the statement "the duration is T2-T1 as measured by those respective clocks". The issue lies in the fact that we have not established a "common time" for both clocks.

If the clock at C2 started one unit of time before the clock at C1 such that when the clock at C1 reads T=0 the clock at C2 reads T=1

then the value T2-T1 will not accurately reflect the journey time for the pulse. If the pulse takes 1 unit of time to reach the clock at C2 then the reading on the clock at C2 will be T=2. Subtracting the two values will give a journey time of 2 units of time.

Now, if the pulse is reflected from the clock at C2

from the clock at C2 but takes 3 units of time in the opposite direction. but takes 3 units of time in the opposite direction, it will arrive at the clock at C1 when that clock reads T=4. Subtracting the two values will give a journey time of 2 units of time. Concluding that the clocks are synced is clearly erroneous given the starting configuration of the system.

Maybe we shouldn't call it a duration then. T1 is what the one clock at the first location reads when the pulse is sent from there. T2 is what the seconds clock reads when the pulse is received from there. Subtracting them gives a figure, and it seems to offend you to call it a duration, which seems fine since indeed, no common time has been established. So we simply have a number that is the difference between the two readings. The clocks literally can say anything, so this value can be any figure at all, positive or negative. So let's just not call it a duration.

You don't know this. You can't make this assumption about something not yet measured.

No reflection is part of the procedure. The pulse can be sent at any time. Yes, it can be done exactly at the moment the signal was received from location C1, but it doesn't have to be. We just need to know what the clock there said when the pulse is sent.

Both differences are empirically measured to be 2, so by Einstein's definition, the clocks are empirically in sync. Only the empirical readings of the clocks were used to determine this.

I noticed that you needed to posit light speed in one direction (something you've asserted cannot be measured, and thus a metaphysical assumption) being thrice that of light going the other direction. You're free to add this strange complication, but it doesn't change the empirical facts.

In the frame in which they stay at their locations, the clocks are still in sync by definition.

I think you need to respond to post 46 which covers the earliest measurement of the speed of light, and which used a one-way method. It would be a long time before a two-way method could be employed. Your argument here seems to hinge on a metaphysical assumption of direction-dependent light speed.

The "one-way" speed of light, from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector. What can however be experimentally measured is the round-trip speed (or "two-way" speed of light) from the source to the detector and back again.Experiments that attempted to directly probe the one-way speed of light independent of synchronization have been proposed, but none has succeeded in doing so.[3] Those experiments directly establish that synchronization with slow clock-transport is equivalent to Einstein synchronization, which is an important feature of special relativity. Though those experiments don't directly establish the isotropy of the one-way speed of light, because it was shown that slow clock-transport, the laws of motion, and the way inertial reference frames are defined, already involve the assumption of isotropic one-way speeds and thus are conventional as well.[4] In general, it was shown that these experiments are consistent with anisotropic one-way light speed as long as the two-way light speed is isotropic.[1][5]

an assumption that is made by standard formulations of the Special Theory of Relativity, but which has no experimental support, and which may even be untestable in principle—the assumption,namely,that the measured one-way speed of light is a constant in all directions in all inertial frames.The natural place to begin is with Einstein,and his original, 1905 formulation of the Special Theory. There, Einstein explicitly assumed that the one-way speed of light is a constant in all inertial frames. He did not,however, view that postulate as one for which there was experimental evidence. His position was rather that,while there is evidence for the assumption that the round-trip speed of light in a vacuum is a universal constant,the further postulate that the time taken for light to travel between two locations is the same in both directions is instead something which one establishes as true ‘by deﬁnition’.194 On Einstein's own approach,therefore,it is simply a matter of convention that the one-way speed of light in a vacuum is a constant.195. This idea that one can view it as true by deﬁnition that the oneway speed of light is a constant is a rather jarring one, and has given rise to a controversy that is still not yet fully resolved. Thus,on the one hand,a number of philosophers, starting with Hans Reichenbach,have strongly defended the view that the non- conventional content of the Special Theory of Relativity precludes any experiment that could be used to determine whether the oneway speed of light is in fact a constant.196 But,on the other hand, a number of proposals have been advanced, and continue to be advanced,by physicists and others,concerning experiments that could be carried out to determine the one-way speed of light. The experiments proposed so far,however, all seem to be ﬂawed,for, upon close scrutiny,all of the experiments appear to involve some principle or other that is true only if the one-way speed of light is a constant,and, if this is right, then none of the experiments proposed so far can possibly result in a value for the one-way speed of light which differs from that of the average round-trip speed.197

Quote from: HalcQuoteIf the clock at C2 started one unit of time before the clock at C1 such that when the clock at C1 reads T=0 the clock at C2 reads T=1You don't know this. You can't make this assumption about something not yet measured.It's called specifying the intial conditions of the experimental set-up.

QuoteIf the clock at C2 started one unit of time before the clock at C1 such that when the clock at C1 reads T=0 the clock at C2 reads T=1You don't know this. You can't make this assumption about something not yet measured.

The pulse can be sent at any time. Yes, it can be done exactly at the moment the signal was received from location C1, but it doesn't have to be.

Let a ray of light start at the “A time” tA from A towards B, let it at the “B time” tB be reflected at B in the direction of A (Einstein, 1905).

Quote from: HalcBoth differences are empirically measured to be 2, so by Einstein's definition, the clocks are empirically in sync. Only the empirical readings of the clocks were used to determine this.I have outlined a case where both differences are empirically measured to be 2, using only the empirical readings of the clocks to determine this. The initial conditions of the set-up were specified such that the clocks were not in sync but still both differences are empirically measured to be 2.

As Alice cannot distinguish between the two scenarios on the basis of empirical observation, this set of empirical observations does not empirically verify the synchrony of the clocks.

But, here's the kicker: there are other empirical observations of the process, all of which show that the clocks aren't synchronised and that the light does take longer to travel in one direction than the other.

You're correct, we are free to add this complication and it doesn't change the empirical facts. It is precisely that the empirical facts are not changed which allows us to draw the conclusion that Alice cannot distinguish between the two empirically and so, she can only rely on assumption to make the statement that her clocks are synced - in a frame dependent manner or an absolute manner.

Alice simply cannot determine this by way of experiment.

I'll take a look at it again. Did you provide the provide the peer reviewed papers?

From what I read you were trying to assert that attempts to measure the one-way speed of light came oh so, very nearly close to providing an exact measurement for the speed of light.

This can be translated as, they demonstrated a variable speeed of light because it wasn't the defined value c.

Until you provide some sort of reference or link, I'm going to go with wikipedia and its references

Following one of the references led me to a book called Time, Tense, and Causation by Michael Tooley:Quotean assumption that is made by standard formulations of the Special Theory of Relativity, but which has no experimental support, and which may even be untestable in principle—the assumption,namely,that the measured one-way speed of light is a constant in all directions in all inertial frames.

an assumption that is made by standard formulations of the Special Theory of Relativity, but which has no experimental support, and which may even be untestable in principle—the assumption,namely,that the measured one-way speed of light is a constant in all directions in all inertial frames.

Now, you can continue to try and frame the discussion however you like, but you there is no escaping the very simple fact that there is no experiment which can empirically determine that two spatially separated events are simultaneous (in any way, frame dependent or otherwise).

Therefore, any conclusion that states that two [specific] events are simultaneous (in any way, frame dependent or otherwise) assumes that conclusion.

It doesn't change the fact that the clocks are synced in that frame by definition, and the premise about them not being synced is shown to be wrong.I think your problem is that you're running with a different definition of being in sync than what Einstein describes. If you want to show an inconsistency with Einstein's interpretation, you need to use his definitions.

we establish by definition that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A.

Let a ray of light start at the “A time” tA from A towards B, let it at the “B time” tB be reflected at B in the direction of A, and arrive again at A at the “A time” t0 A.In accordance with definition the two clocks synchronize if tB - tA = t' A - tB

You're making an assumption that gets contradicted by the empirical measurement taken. The empirical test (the numbers you provided in your example) trumps the assumption, proving it incorrect. You can't presume the peg to be square and measure it to be round and expect the presumption to still hold.

The guy is in the history books as the first to measure light speed. If his peers found his methods invalid, he would not hold that honor. It gained support by Newton and others and was confirmed 50 years later by different methods.I also mentioned that you're probably looking for review from your peers, not his. Do some thinking for yourself for once and tell me what's wrong with his methods.

[moved up] But I assert that the test can be run today with under 1% error. Why can't a similar experiment be run today with our far more accurate clocks and such?

If we compare the one-way experiments of [48] in Fig. 7 with the two-way experiments in Fig. 6, the results are about 4 to 6 orders of magnitude smaller in the one-way experiments than those of two-way experiments. Also the most recent one-way experiment performed by Krisher et al [79] in 1988 in NASA- Jet Propulsion Laboratory Deep Space Network (DSN) presents 2 orders of magnitude smaller values than that of NASA‟s previous experiment by Vessot et al [77, 78] in 1976. This is contradictory to our expectation based on STR [the Special Theory of Relativity] where we expect lower order of magnitude values with greater improvements.The results of the one-way experiments are increasing in magnitude with time, whereas, the two-way experiments are decreasing in magnitude with greater precision and improvements with time. However, the results from the limits of the one-way experiments of [11] at the GRAAL facility are consistent with STR. But the regularity in the variations of the reported results of the GRAAL measurements reported in [11] in different timeperiods remains unclear and needs further experimental investigations.=================you'll like this part=================We have presented a comparison of experiments in Fig. 8 that shows the one-way speed of light measurement is approximately 2000 times more sensitive than that of round-trip test. Will [48] showed that experiments which test the isotropy in one-way or two-way (round-trip) have observables that depend on test functions but not on the particular synchronization procedure. He noted that “the synchronization of clocks played no role in the interpretation of experiments provided that one is careful to express the results in terms of physically measurable quantities”. Hence the synchronization is largely irrelevant and one-way speed of light is measurable.Results of the experimental tests spanning at least 24 hours periods in different seasons of the year should be recorded. Any hypothetical diurnal variations that might be observed should follow the figures presented in the section 2.2 in Fig. 3 and Fig. 4.

Some authors such as Mansouri and Sexl (1977)[9][10] as well as Will (1992)[11] argued that this problem doesn't affect measurements of the isotropy of the one-way speed of light, for instance, due to direction dependent changes relative to a "preferred" (aether) frame Σ. They based their analysis on a specific interpretation of the RMS test theory in relation to experiments in which light follows a unidirectional path and to slow clock-transport experiments. Will agreed that it is impossible to measure the one-way speed between two clocks using a time-of-flight method without synchronization scheme, though he argued: "...a test of the isotropy of the speed between the same two clocks as the orientation of the propagation path varies relative to Σ should not depend on how they were synchronized...". He added that aether theories can only be made consistent with relativity by introducing ad-hoc hypotheses.[11] In more recent papers (2005, 2006) Will referred to those experiments as measuring the "isotropy of light speed using one-way propagation".[6][12]However, others such as Zhang (1995, 1997)[1][13] and Anderson et al. (1998)[2] showed this interpretation to be incorrect. For instance, Anderson et al. pointed out that the conventionality of simultaneity must already be considered in the preferred frame, so all assumptions concerning the isotropy of the one-way speed of light and other velocities in this frame are conventional as well. Therefore, RMS remains a useful test theory to analyze tests of Lorentz invariance and the two-way speed of light, though not of the one-way speed of light. They concluded :"...one cannot hope even to test the isotropy of the speed of light without, in the course of the same experiment, deriving a one-way numerical value at least in principle, which then would contradict the conventionality of synchrony."[2] Using generalizations of Lorentz transformations with anisotropic one-way speeds, Zhang and Anderson pointed out that all events and experimental results compatible with the Lorentz transformation and the isotropic one-way speed of light must also be compatible with transformations preserving two-way light speed constancy and isotropy, while allowing anisotropic one-way speeds.

You've mistakenly assumed that I am trying to demonstrate an inconsistency or contradiction in the Einsteinian interpretation and it is against this contention that you are arguing. You might be drawing inferences from other threads that I have started and incorrectly applying them in the context of this disucssion.

What I'm not doingLet me state it once again: I am not trying to show an inconsistency with Einstein's interpretation - at least not in this line of discussion.

While the observer in the "stationary" frame is performing this clock synchronisation, they observe a relatively moving observer perform the exact same synchronisation process. They are also located midway between 2 clocks. The light pulses are sent to each clock and reflected; crucially, the "stationary" observer sees the light pulses hit each clock not-simultaneously, get reflected, and arrive at the "moving" observer simultaneously. The "moving" observer concludes that their clocks are synchronised. The "stationary" has observed that the clocks are not synchronised.Here, in the original thought experiment, we are provided with a clear case of why the assumption of synchronisation/simultaneity is unjustified.

What I am doingWhat I am saying, however, is that the conclusions of the Einsteinian interpretation are assumed i.e. the conclusions are arrived at through circular reasoning.

What is requiredIn order to demonstrate this circular logic we need only present an alternative interpretation of the evidence

In order to do this we need only demonstrate that there is no way to distinguish between the two cases by way of empirical observation.

Quotewe establish by definition that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A.This is the part that cannot be determined by way of empirical observation. It is an assumption, plain and simple. This is the expressed assumption.

then bouncing a light signal from A to B and back to A IF" tB - tA = t' A - tB then in accordance with definition the two clocks synchronize.

This is all fine, there is absolutely no problem with any of that. Incidentally, you might not recognise it bcos it isn't expressly stated, but the initial conditions that are implied include synchronised clocks.

We can start with different initial conditions however and say:IF we start with two clocks that aren't syncronised, with one having started 1 unit of time before the other and IF we assume that the time from A to B is 1 unit of time while the time from B to A is 3 units of time

Here we have two different scenarios - one with clocks synchronised, one with clocks not synced - with the exact same empirical evidence. There is therefore, no way to distunguish between the two by way of empirical observation.

Now, it might be tempting to jump to the conclusion that choosing one over the other represents an equal assumption

but you'd be wrong, because the two scenarios - despite the empirical equivalence - are not equal.

Relativity of SimultaneityAs has been mentioned, there are two parts to the relativity of simultaneity:1) Events which are simultaneous in one frame (the "stationary system")2) are not simultaneous in relatively moving inertial frames

It is number 1 above that is in contention because there is no experiment which can be carried out to reliably determine the simultaneity of spatially separated events.

This is a direct consequence of the Galilean Principle of Relativity. When light signals arrive at an observer simultaneously from two equidistant locations (in the physical world), they cannot rule out the possibility that they were advancing towards one light signal, while retreating from the other.

We are free to choose any initial conditions for the experiment that we choose

Quote from: HalcI also mentioned that you're probably looking for review from your peers, not his. Do some thinking for yourself for once and tell me what's wrong with his methods.Well, I wouldn't be so presumptuous to assume that I am a peer of those scientists who peer review papers for inclusion in journals

I also mentioned that you're probably looking for review from your peers, not his. Do some thinking for yourself for once and tell me what's wrong with his methods.

He's in the history books because he demonstrated that the speed of light is finite, when the thinking at the time was that it was infinite/instantaneous. He isn't in the history books bcos his measurement in any way verifies that the one-way speed of light is constant, in all directions, in all inertial frames and is equal to the value represented by c.

His measurement was off by about 25%, as you mentioned. So, if you're holding this up as evidence for Einstein's interpretation of relativity, I'm arfraid you are achieving the opposite. If it were to be taken as a serious experimental test of Einstein's relativity it would invalidate it.

Is that the answer that "[my] peers" give? You seem to know better than me who these "peers" are.

You tell me! It would seem that for all of the experimental verification of Lorentz-Poincare Einsteinian relativity

You state, in this thread, that Alice makes one claim that is contradicted by some alternate claim by Bob. You seem to leverage this assessment of contradiction in order to push whatever alternate position (this atemporal universe as the title calls it) that you hold.It would be a contradiction in the interpretation if they actually made contradictory claims as you state. I've been taking the position that all their claims are entirely consistent.My bold. You misrepresent the claims of the two observers (later to be named Alice and Bob) and also lay claim that assumptions were made (none were other than assumptions of the premises of SR, neither of which mention simultaneity). It is that statement that prompted me to jump into this thread. The entire thread since then seems to have been about this, despite your claim here that it is not what you are doing. If you're not intending to show inconsistency with the interpretation, then don't claim said inconsistency in your OP like that.Say it is fine, but here is some alternate interpretation. I notice that nobody is discussing that since you've taken the hostile route and declared the mainstream interpretation to be wrong.

You need to be far more explicit that this empty statement here. The conclusion you seem to claim to be assume is the simultaneity of a pair of clocks in a given frame, but since a statement concerning simultaneity is not part of either of the premises of the interpretation, this doesn't hold water. Maybe you mean something else. Say it clearly instead of vacuously like that. There are exactly two assumptions made, and neither of them is listed as a conclusion.So if your purpose here is to do that, you need to name the assumption that is the same as the conclusion. Without that, there is no circularity, only A that leads to B without any additional assumptions. B doesn't lead back to A. Show me a circle, or your claims of this circularity are empty.

There are valid alternative interpretations. In what possible way would that be evidence of the circularity of the first interpretation?...Of course there is no way. They wouldn't be interpretations if there was an empirical way to distinguish them. You don't need to demonstrate this since nobody asserts otherwise.But none of this supports a claim that any interpretation assumes its conclusions.

The mainstream alternative interpretation keeps constant light speed but replaces Galilean relativity with one where position become a property instead of a relation. The sync definition outlined by Einstein still works perfectly in this interpretation.You're suggested discarding the constant light speed premise as well. Then the sync definition doesn't work anymore. It is a strange interpretation, but not invalid if that's what you want to go with. Not sure if it is actually valid. Have to think about it.

It directly follows from the 2nd premise of SR. Even an absolute interpretation assumes that premise. Perhaps your interpretation does not. Anyway, it isn't a 3rd premise. It follows from the 2nd. No additional assumptions have been made.

Not an assumption. That is necessary given constant light speed.

They are synchronized. The action doesn't synchronize the clocks if they were not before we did this.

The wording here makes it sound like the latter.

QuoteThis is all fine, there is absolutely no problem with any of that. Incidentally, you might not recognise it bcos it isn't expressly stated, but the initial conditions that are implied include synchronised clocks.Not so. It was a conditional. Iff they are synchronized, the condition tB - tA = t' A - tB will be met, and if they are not, that condition will not be met. Alice need not assume the clocks are in sync in order to run the test.

No you cannot. This violates the 2nd premise. Work out your own sync convention if you want to go with a different set of premises. I stated above that the convention doesn't work if that premise is dropped. Even most absolute interpretations keep that premise, thus making this sync convention valid under them.

That why your alternate interpretation might be valid. It's why they're called interpretations.

Meaningless statement under the relative interpretation. You are using language from a different interpretation. That makes you the one making additional assumptions.

If they're in violation of the premises of a given interpretation, they are initial conditions for a different interpretation, and in no way invalidates the first interpretation.

His experiment can be reproduced today with modern measuring devices.

I am looking to you for a reason why his non-round-trip method is an invalid method to measure light speed. Don't quote other sites which you interpret as asserting that it cannot be done. Tell me why it can't be done.

Suppose light moved at thrice the speed in one direction as the other. Wouldn't Roemer see triple the time if he did the experiment in one direction as the other?

You evade this question because it is an apparent inconsistency in your 'initial condition' that not even the absolutist interpretation will take. Resolve the inconsistency or conisder that interpretation to be falsified.

Are you asserting that modern measurements would still be off by 25%? That would indeed quickly falsify all modern interpretations, including LET, which still presumes direction independent light speed. Here's your chance to be famous. The experiment is pretty trivial. Surely somebody would have noticed by now.

I see you continue to quote wiki pages unrelated to what Roemer was doing.He wasn't testing isotropy. He was measuring light speed using a one-directional method.