The only true thought experiments are those performed outside of a laboratory setting where the participants are unaware they're participating in one, and as such are illegal in most cases. Well that's not true, unethical is the word. Which is the foundation of how most today operate. Dating, for example.

"Would you rather [undesirable choice A. vs. undesirable choice B.]..." seems to be the casual go-to.



But as far as contemporary philosophy goes, the trolley problem comes to mind. It's fairly basic yet touches on the main issues of life and society. Life, death, responsibility, action and inaction, blame, guilt, cause and effect, etc..

Any question that requires you to put yourself in another person's situation and decide what you would you do in their place. This is a game we sometimes play with movies: If you were the protagonist... If you were the perpetrator... If you were the wronged wife... If you were the best friend... how would you handle this?

Tie between Violinist Analogy and Trolley Car

Mine is variations on the Branch Line Case from Parfit,

It’s just so juicy

What if a demon crept after you into your loneliest loneliness some day or night, and said to you: "This life, as you live it at present, and have lived it, you must live it once more, and also innumerable times; and there will be nothing new in it, but every pain and every joy... — Vaskane

I think there's a pretty good chance that's just reality. Without the creepy demon.

I think The Ones Who Walk Away from Omelas can be applied to many moral questions. "The city's constant state of serenity and splendor requires that a single unfortunate child be kept in perpetual filth, darkness, and misery. Once citizens are old enough to know the truth, most, though initially shocked and disgusted, ultimately acquiesce to this one injustice that secures the happiness of the rest of the city. However, some citizens, young and old, walk away from the city after seeing the child".

Is the life of suffering experienced by factory farmed animals permissible for the pleasure it brings us?

In reference to the last question I’d say no because I think animal exploitation is wrong and we can still have pleasure, convenience and entertainment without them.

What are your favorite thought experiments and why? — Captain Homicide

The emperor's new clothes. Innocence and frankness is a lost quality in the way we think.

Time doesn't exist for a freely moving photon. But when they are slowed down to a snail's pace time catches up.

Is that anything like a hangover?

In reference to the last question I’d say no because I think animal exploitation is wrong and we can still have pleasure, convenience and entertainment without them. — Captain Homicide

Do you still contribute to the animal farming industry though, or have you walked away from Omelas?

Once citizens are old enough to know the truth, most, though initially shocked and disgusted, ultimately acquiesce to this one injustice that secures the happiness of the rest of the city. However, some citizens, young and old, walk away from the city after seeing the child — Down The Rabbit Hole

After a human dies, it 'disassembles.' My fav thought is to 'tag' every sub-atomic sized particulate that departs from a human after death, and track each one, to see where it ends up. I wonder how much of a living humans atoms (or quarks and electrons), were, in all of human history, part of previous humans that have lived.
How much of 'us' is 'naturally recycled' after we die?
How much are we physically, part of all that has lived and died before us?

Time doesn't exist for a freely moving photon. But when they are slowed down to a snail's pace time catches up. — jgill

Do you think that if a human travelled at light speed ( I know that human 'mass' currently makes that impossible) then the human would not age?
I think we would age at exactly the same rate that we do now, but within a different temporal reference frame.

Do you think that if a human travelled at light speed ( I know that human 'mass' currently makes that impossible) then the human would not age? — universeness

Now, that's a nice thought experiment. There would be no concept of time, and aging requires the existence of time it seems to me. This takes one back to a previous thread on change and time: does a physical change require a passage of time? For our little scamp, the photon, one has to ask if it changes other than position?

Attention physicists. Chime in if you are in the house. :cool:

Do you still contribute to the animal farming industry though, or have you walked away from Omelas? — Down The Rabbit Hole

I still eat meat though this is out of practicality regarding my individual circumstance rather than me approving of animal exploitation. If I had the means to live a vegan lifestyle I would.

I think that is the basis of the thought that is supposed to have started Einstein on his quest for answers, when he tried to imagine himself. 'hitching a ride on a photon.'
But if QFT is correct then there is no such an object as a free particle, there are only field excitations/disturbances. Which for me, suggests that we must be constructions of field excitations, yes? We sure need those physicists. Where are you @Jaded Scholar?

I think that is the basis of the thought that is supposed to have started Einstein on his quest for answers, when he tried to imagine himself. 'hitching a ride on a photon.' — universeness

From memory, I think you're exactly right about that.

But if QFT is correct then there is no such an object as a free particle, there are only field excitations/disturbances. Which for me, suggests that we must be constructions of field excitations, yes? — universeness

This is true, but I think in this context, the existence of "you" requires the sustained existence of those excitations, which are generally constricted to follow the rules of special relativity (sorry, but I have avoided talking about the Reeh–Schlieder theorem because I do not entirely understand how well it acts as an analogue for quantum entanglement), unlike the field itself which has much more wiggle room in terms of relativistic causality.

So I'm not 100% certain, but even within QFT, I think the question does reduce to the implication raised above: that if you could be accelerated to the speed of light, time would cease to pass for you at all.

Do you think that if a human travelled at light speed ( I know that human 'mass' currently makes that impossible) then the human would not age? — universeness

According to Special Relativity, this is exactly what would happen, and you are right in noting that massive objects cannot reach the speed of light, but I think it's worth mentioning that it's only "impossible" because it would require an infinite amount of energy to do so - so it's more that the theory implies that it can't happen, but if it somehow could, SR is pretty clear that your local time would pass more and more slowly as you accelerated and would stop entirely at v=c. At that velocity, everything within your timeframe would effectively stop - the entire lifespan of the universe (even if it's infinite) would zoom past you. You're not wrong in saying that you would continue aging, just in a different temporal reference frame, but "continue" is maybe an ambiguous term in a reference frame where time has reached the limit of not passing at all.

However, makes a very interesting observation, noting that not everything that affects you is from within your own timeframe:

There would be no concept of time, and aging requires the existence of time it seems to me. This takes one back to a previous thread on change and time: does a physical change require a passage of time? For our little scamp, the photon, one has to ask if it changes other than position? — jgill

Of course, we do interrupt photons all of the time to take them out of their timeframe and merge them with matter. And I need to get into the weeds to mention that a human travelling at the speed of light would still be human-sized in the direction of travel (if infinitessimally thin when viewed from the side), so if you started your lightspeed journey in a non-empty universe, it's a safe bet that you would lose a few pieces of yourself before the end of time (probably all of them). Which I agree could conceivably qualify as an alternate definition of aging.

I haven't done the maths myself, but I actually read about some practical estimates on this exact thing in Bill Bryson's "A Short History of (Nearly) Everything" (my favourite book): I'm not sure what portion of a body generally gets dispersed to become part of another human or any other organism, but for anything short of a hermetically-sealed chamber, the amount is always nonzero. Whether you are buried, cremated, etc., it only takes a few centuries before a substantial portion of the atoms that comprised you have gotten into the atmosphere and circulated through various physical processes, ultimately distributing very far and wide, including into the atomic makeup of every other human that currently lives. At least a few dozen of the atoms in your body were once part of Isaac Newton, a few dozen were part of Socrates, Cleopatra, Ghenghis Khan, and even the long-forgotten hominid who first artifically kindled fire. But, to continue (roughly) plagiarising Bill Bryson, the process does require a few centuries - you are not yet one with, say, Elvis Presley.

This is pretty vanilla, but one of the thought experiments I appreciate most is Galileo's thought experiment demonstrating that the nature of gravity cannot involve heavier objects falling faster than lighter objects - the prevailing view at the time (late 16th century).

Imagine a heavy ball falling at a rate V_h. Then imagine two smaller balls, which, because they are lighter, fall at a slower rate, V_l. If you connect them with a long rope, do they still fall at the rate V_l? When you shorten that rope, do they still fall at V_l? What if you make that rope shorter and shorter, up to the point where they are touching each other, but still separate objects - do they fall at V_h or V_l? What if they are pressed together, as two halves of the heavy ball? Do they fall slower just by the very act of imagining them to be separate? Clearly, this is ridiculous. The source of some objects falling slower than others cannot be a difference in how gravity affects heavy and light objects, but must be due to some other factor (air resistance). Without this external factor, even a hammer and a feather would fall at the same rate.

And it was beautiful to learn that the astronauts who went to the moon on the Apollo 15 mission actually brought a hammer and a feather with them, to televise them falling at the same rate, vindicating Galileo's hypothetical claim, 300 years later. :')

Wow! ('Very Valuable Scholar,' a.k.a, 'Jaded Scholar,') those were very interesting posts indeed.
Firstly, thank you for your various conformations regarding my own, small 'related to' physics, knowledge base.

Next:

This is true, but I think in this context, the existence of "you" requires the sustained existence of those excitations, which are generally constricted to follow the rules of special relativity (sorry, but I have avoided talking about the Reeh–Schlieder theorem because I do not entirely understand how well it acts as an analogue for quantum entanglement), unlike the field itself which has much more wiggle room in terms of relativistic causality. — Jaded Scholar

I have no knowledge of the Reeh-Schlieder theorem, but, after I have finished this post, I will start to learn about it, until my current physics grasp gets overwhelmed again, but I am sure my efforts will expand my understanding a little, so thanks for directing me to the theorem.

SR is pretty clear that your local time would pass more and more slowly as you accelerated and would stop entirely at v=c. At that velocity, everything within your timeframe would effectively stop - the entire lifespan of the universe (even if it's infinite) would zoom past you. You're not wrong in saying that you would continue aging, just in a different temporal reference frame, but "continue" is maybe an ambiguous term in a reference frame where time has reached the limit of not passing at all. — Jaded Scholar

But these points are all based on the relative reference frame of an observer, yes?
To an observer, I would not seem to age, if I was travelling at light speed, but in my own temporal reference frame, I would.
Is there any physics that indicates that I would not live my normal human lifespan, relative to any other object that exists with me, in that same 'light speed,' temporal reference frame?

Is this just an intuitive prediction based on:
The Earth rotates at approx 1,000 mph. Earth orbits the Sun at approx 67,000 mph. Our solar system orbits the centre of the Milky Way at approx 514,500 mph, the Milky Way is moving at approx 1.5 million mph and we also have the expansion rate:
"More recently, using Type Ia supernovae, the expansion rate was measured to be H0 = 73.24 ± 1.74 (km/s)/Mpc. This means that for every million parsecs of distance from the observer, objects at that distance are receding at about 73 kilometres per second (160,000 mph)."
Regardless of all these relative speeds, I still age as I do, in my current temporal reference frame, so I 'intuit' that regardless of my speed 'relative' to any other existent in the universe. I will always age at the rate I do, due to my own personal 'entropy,' is that not true?

So, photons do age, in their own temporal reference frame, from the stand point that they had an instant of becoming and they exist until such as, a moment of absorption?
Is this flawed thinking from a physics perspective, or more specifically a quantum physics perspective? Perhaps a better question to ask is are photons immune to entropy?

does a physical change require a passage of time? For our little scamp, the photon, one has to ask if it changes other than position? — jgill

As jgill indicates above, if a photon changes position and can be absorbed and emitted, then it must experience duration, or is this again, just an incorrect 'intuitive' thought based on 'classical' notions of physical reality.

A further point, might be the suggestion that an observer would never see a spaceship fall into a black hole, it would seem to be frozen in time, at the event horizon, BUT, the spaceship would actually fall into the black hole (and get spaghettified,) yes?

I haven't done the maths myself, but I actually read about some practical estimates on this exact thing in Bill Bryson's "A Short History of (Nearly) Everything" (my favourite book): I'm not sure what portion of a body generally gets dispersed to become part of another human or any other organism, but for anything short of a hermetically-sealed chamber, the amount is always nonzero. Whether you are buried, cremated, etc., it only takes a few centuries before a substantial portion of the atoms that comprised you have gotten into the atmosphere and circulated through various physical processes, ultimately distributing very far and wide, including into the atomic makeup of every other human that currently lives. At least a few dozen of the atoms in your body were once part of Isaac Newton, a few dozen were part of Socrates, Cleopatra, Ghenghis Khan, and even the long-forgotten hominid who first artifically kindled fire. But, to continue (roughly) plagiarising Bill Bryson, the process does require a few centuries - you are not yet one with, say, Elvis Presley. — Jaded Scholar

This is fascinating. I have heard this book in audio on youtube, but I have always fallen asleep to it in the past, perhaps I should buy a paper copy and read it properly :blush:
You would think such scientific findings, would help to alleviate the human fear of death, in that we are all, and in the main, always have been, partly, varieties of all who have lived before.
If human consciousness is ever proven, to be also quantisable, then perhaps each new human consciousness is also partly, built on spare parts of disassembled consciousnesses that have existed in the past. I find that 'religion,' more plausible than any other I know of, but it's not panpsychism or any kind of woo woo theosophism, imo. For me, the word religion is very soiled however. I am with Hitchens in his insistence that 'all religion is pernicious.'

And it was beautiful to learn that the astronauts who went to the moon on the Apollo 15 mission actually brought a hammer and a feather with them, to televise them falling at the same rate, vindicating Galileo's hypothetical claim, 300 years later. :') — Jaded Scholar

Yes, especially when it's so 'intuitive' (I realise this is a problem when it comes to my own thinking,) to assume that heavier (or more dense) objects would fall faster, especially when it is true that heavier/more dense object do create 'more' gravity.
Is gravity a push, a pull, or not a force at all, but a consequence of geometric spacetime warping.
I think this wee 15min vid is a good one, for making the main points involved (it also mentions your Galileo contribution).

I have no knowledge of the Reeh-Schlieder theorem, but, after I have finished this post, I will start to learn about it, until my current physics grasp gets overwhelmed again, but I am sure my efforts will expand my understanding a little, so thanks for directing me to the theorem. — universeness

:lol: I think I would need both @Jaded Scholar and @jgill to 'baby step me,' over all the hurdles presented to me by the Reeh-Schlieder theorem. Either that or become a mature student at uni again and gain a maths and then a physics PHD.

I just kept trying to drill deeper and deeper, using provided links, starting with a wiki entry.
From even this first sentence, I soon became overwhelmed:
The Reeh–Schlieder theorem is a result in relativistic local quantum field theory published by Helmut Reeh and Siegfried Schlieder (1918-2003) in 1961.
I clicked on the 'local quantum field theory' link, which took me to:
Algebraic quantum field theory (AQFT) is an application to local quantum physics of C*-algebra theory. Also referred to as the Haag–Kastler axiomatic framework for quantum field theory, because it was introduced by Rudolf Haag and Daniel Kastler (1964). The axioms are stated in terms of an algebra given for every open set in Minkowski space, and mappings between those.
So, I then had to click on the 'C*-algebra ' link and the 'Minkowski space' link, after I tried to follow the Haag–Kastler axioms, with limited success. :rofl:

I think I will stick to what I can garnish from youtube vids by the likes of Sabine Hossenfelder, Sean Carroll, Carlos Rovelli, Brian Cox, Jim Al Khalili, and other such 'science presenters/popularisers,' that put out their attempts to explain the basics for folks like me.

Well, I'm still stuck with Hume's "Skepticism with Regard to the Senses."

The thought experiment consists in looking at objects to attempt to get the idea of a continued existence of objects as well as trying to find the reasons for why we believe objects to exist in a manner distinct from our perceptions of them.

We can't. Yet we do assume both, quite strongly, yet we don't have good reasons for doing so. It's really hard. But fascinating notwithstanding the futility of such an exercise, it's an obsession.

Yet we do assume both, quite strongly, yet we don't have good reasons for doing so. — Manuel

Using this argument we can never have a reason to believe in the world becuase we can’t ever escape our senses short of omnipotence and even then you wouldn’t know if it wasn’t just another simulation.

It's not doubting that there is an external world, Hume never doubts this, what he is pointing out as problematic is in having an idea of external existence which is different from our specific perceptions of them.

But fascinating notwithstanding the futility of such an exercise, it's an obsession. — Manuel

Where do you get off the train? (meaning, at what point do you hit the 'its now a futile endeavour' line in your enquiry?)

Where do you get off the train? (meaning, at what point do you hit the 'its now a futile endeavour' line in your enquiry?) — AmadeusD

I don't think it's of much difference to other issues like freedom of the will, or matter thinking, personal identity and so on.

You get off whenever you get tired of it or bored with it or find a unique approach that may be somewhat satisfactory.

I actually find BIV (brain in a vat) a boring thought experiment. It is because you are given a scenario already pre-arranged so that everything is as it is now, except you are actually hooked up in a machine simulation. And then the scenario asks you to argue whether your knowledge or belief is a true belief. To me it is a dumb thought experiment.

Had some thoughts about Doppelgangers inspired by Karl Pilkington and then a film I saw recently called Infinity Pool:

Imagine there is a world where doppelgangers can be created identical to other people in terms of biological structure, genes, memories, abilities, absolutely everything.

Some questions:

1. If a doppelganger was created of you, how do you know you are not the doppelganger? Could you convincingly win an argument with your doppelganger about who was the real doppelganger?

2. What if you were met with this same doppelganger scenario but from another family member or friends. You could only pick one to bring back to your life with you and you would never see the other again.

how do you know you are not the doppelgan — Apustimelogist

This depends on whether the 'identical' memories include the moment at which the DG was created. Typically, you'd have that memory (i.e, you could remember before and after the creation because you knew it happened) where the DG could not.
I think this is why the Teletransporter TE is so good - it stipulates that this isn't the case and that both versions had the 'exact' same memories. I suppose another version is to stipulate that you don't know the DG was created. Same issue

Yes, this is a very good point. I think it would have to be something like you go under a medical procedure and wake up afterwards having gained a doppelganger. Then I imagine your memories would be lined up.