7 ms·

Einstein’s Thought Experiments

drewcoo 6y ago
The thought experiment did not originate with Einstein. The name gedankenexperiment predates him and Maxwell's use of the concept. So the article also misreports the origination with Maxwell. Maybe they should have skipped the couching in history if they didn't know the history or even want to look it up. And now that I'm reading the article's comments, other readers have also made those points. This article is useful as a tackle dummy for skeptics but not much else.
- holidayacct 6y ago
  Thank you, I read the title and was trying to figure out what this person was talking about. There are references to thought experiments going back to the Ancient Greece and Rome.
- Jyaif 6y ago
  It's pretty obvious that thought experiments have existed for a long time ("If I kill him, I can mate with the females"). I think what the blog post is saying is that thought experiments applied to physics became popular with Einstein.
  - guerrilla 6y ago
    This is also wrong. Everyone from Aristotle to Newton and onward to Einstein were doing thought experiments in physics the entire time.
- typon 6y ago
  Ibn Sina proposed the famous "Floating man" thought experiment a thousand years ago
  - throwaway_pdp09 6y ago
    You couldn't have... you know...? https://en.wikipedia.org/wiki/Floating_man https://en.wikipedia.org/wiki/Floating_man
- mellosouls 6y ago
  Thought experiments probably go back as far as thinking. Plato's Cave and Zeno's paradoxes are famous ancient ones; the article is rather misleading in its association of them with recent times.
  - pravus 6y ago
    This was my thought as well. I have no idea why a special term is ascribed to physicists for just thinking logically.
reeboo 6y ago
"You see, Einstein had a problem with it because it seems to conflict with the speed of light limit in Special Relativity. We know today that this is not the case, quantum mechanics does not conflict with Special Relativity because no useful information can be sent between entangled particles." -- So how does quantum communication work? I thought it leveraged entanglement to convey information such that it became untamperable.
- roywiggins 6y ago
  Quantum entanglement can't be used to send information without also sending some photons or other signal between two locations. That's one problem Einstein had with entanglement- at the time, it looked like entanglement might let you send information "at a distance" without transmitting anything. It turns out that entanglement is real but it conspires to prevent any entangled correlations from actually conveying classical information on their own.[0] The idea behind quantum cryptography is to send photons from A to B that are specially prepared so that any attempt to read those photons in flight would be detected. You use these photons to pick a shared key, and then communicate between A and B using that key via a classical channel. If you detect someone snooping on the initial key exchange, you can toss that key and try again. [0] https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem
- btouellette 6y ago
  Quantum communication isn't communication in the sense that you can decide what to send. You have a shared quantum state due to entanglement and you can guarantee that both sides see the same information when they observe the state but it's more like putting two identical messages into sealed envelopes and sending them off to be opened later (with the caveat that because the message hasn't been determined until it is observed you can prevent anyone from knowing what it is ahead of time). Much more detailed explanation here: https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-reasons-quantum-entanglement-doesnt-allow-faster-than-light-communication/#1882b3403a1e https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-r...
  - attilakun 6y ago
soul4krsna 6y ago
Einstein read, studied and ate the Bhagavad-gita everyday. That's why his work is sound. Because the knowledge was revealed.
sidcool 6y ago
I did not get the point: "No useful information can be sent in quantum entanglement". Has it been found how entanglement actually works?
- attilakun 6y ago
  If you are familiar with probability theory, think of it like this: whatever you do with an entangled particle, it will never change other entangled particles' marginal probability, only the joint.
  - da39a3ee 6y ago
    That's very helpful thanks, I do understand what that means but I didn't know I should/could think of entanglement like that.
- thereisnospork 6y ago
  An attempt at lay terms: imagine particles are tiny hands, and they can switch between being left hands and right hands. So to 'entangle' two particles is to make them shake. This means we now know that one particle is a lefty and the other a righty (two lefts can't shake each other) but because they are so small we don't know which is which. Now (gently) separate the two particles and place each in a box. It is presently unknown which is lefty, and which is righty so at this point each particle is considered to be in a superposition of both lefty and righty. A la Schrodingers cat each particle '''hasn't decided''' if it is a left or right. All QE states is that when we look in one box and see a right hand we know the other box contains a left hand - regardless of the distance between them. There is no provision or mechanism for shaking one particle and having a change occur with the other (information transfer).
  - sidcool 6y ago
    That's a good explanation. However, since the particles are in superposition, the act of observation must be conveyed to the other particle, right?
segfaultbuserr 6y ago
> Well, the demon needs to have information about the motion of the atoms, otherwise it does not know when to open the door. The interesting thing about Maxwell’s demon is that it tells us entropy is somehow the opposite of information, you can use information to decrease entropy. It's the first connection between the laws of physics and the process of computing, although it's a modern reinterpretation (the original interpretation only argued measurements by the demon requires energy). An interesting implication is: all computers in this universe must generate heat because information is lost in the logic circuit. However, if we can construct the logic circuit in such a way that all information is preserved at the output (i.e. reversible) [0], this computer only needs an infinitesimal amount of energy to operate. Also a fun fact: Do you know that the term "daemon" for background processes was originally named after Maxwell's demon? [1] [0] https://en.wikipedia.org/wiki/Reversible_computing https://en.wikipedia.org/wiki/Reversible_computing [1] https://en.wikipedia.org/wiki/Daemon_(computing)#Terminology https://en.wikipedia.org/wiki/Daemon_(computing)#Terminology
bawana 6y ago
Sabine has made a name for herself being a contrarian. https://www.youtube.com/watch?v=sZI8-9i0SOo https://www.youtube.com/watch?v=sZI8-9i0SOo https://blogs.scientificamerican.com/cross-check/physicist-sabine-hossenfelder-fears-theorists-lacking-data-may-succumb-to-wishful-thinking/ https://blogs.scientificamerican.com/cross-check/physicist-s... She'll even take your money to answer your questions if you dont like physics forums https://www.aps.org/publications/apsnews/201611/hossenfelder.cfm https://www.aps.org/publications/apsnews/201611/hossenfelder... I dont mean to sound critical, but her statements remind me of Lord Kelvin's statement "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" Personally, I think theoretical physics should never be discussed in the absence of the specific data it is trying to address. So much confusion happens when the details are not understood first before the grand theory is proposed. Theories too often are presented as gifts from the heavens and without the corpus to which they speak.
- platz 6y ago
  - your initial comments are only ad-hominem - i don't think kelvin's statement represents her views - Being against a new collider does not mean one takes the position of Kelvin, or is anti-science. She doesn't argue against investment in novel science. Her argument is that a larger collider is the wrong kind of investment to make, based on what we've already observed at the LHC
- dnautics 6y ago
  > "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" It's not being critical, it's just a mischaracterization. I think that Sabine very much thinks there are new things to be discovered in physics, and she is taking an opinionated stance about what is the right way to get to them. > I think theoretical physics should never be discussed in the absence of the specific data it is trying to address. That's exactly what Sabine says.

The thought experiment did not originate with Einstein. The name gedankenexperiment predates him and Maxwell's use of the concept. So the article also misreports the origination with Maxwell. Maybe they should have skipped the couching in history if they didn't know the history or even want to look it up. And now that I'm reading the article's comments, other readers have also made those points. This article is useful as a tackle dummy for skeptics but not much else.

holidayacct 6y ago
Thank you, I read the title and was trying to figure out what this person was talking about. There are references to thought experiments going back to the Ancient Greece and Rome.
Jyaif 6y ago
It's pretty obvious that thought experiments have existed for a long time ("If I kill him, I can mate with the females"). I think what the blog post is saying is that thought experiments applied to physics became popular with Einstein.
- guerrilla 6y ago
  This is also wrong. Everyone from Aristotle to Newton and onward to Einstein were doing thought experiments in physics the entire time.
typon 6y ago
Ibn Sina proposed the famous "Floating man" thought experiment a thousand years ago
- throwaway_pdp09 6y ago
  You couldn't have... you know...? https://en.wikipedia.org/wiki/Floating_man https://en.wikipedia.org/wiki/Floating_man
mellosouls 6y ago
Thought experiments probably go back as far as thinking. Plato's Cave and Zeno's paradoxes are famous ancient ones; the article is rather misleading in its association of them with recent times.
- pravus 6y ago
  This was my thought as well. I have no idea why a special term is ascribed to physicists for just thinking logically.

reeboo 6y ago

"You see, Einstein had a problem with it because it seems to conflict with the speed of light limit in Special Relativity. We know today that this is not the case, quantum mechanics does not conflict with Special Relativity because no useful information can be sent between entangled particles." -- So how does quantum communication work? I thought it leveraged entanglement to convey information such that it became untamperable.

roywiggins 6y ago
Quantum entanglement can't be used to send information without also sending some photons or other signal between two locations. That's one problem Einstein had with entanglement- at the time, it looked like entanglement might let you send information "at a distance" without transmitting anything. It turns out that entanglement is real but it conspires to prevent any entangled correlations from actually conveying classical information on their own.[0] The idea behind quantum cryptography is to send photons from A to B that are specially prepared so that any attempt to read those photons in flight would be detected. You use these photons to pick a shared key, and then communicate between A and B using that key via a classical channel. If you detect someone snooping on the initial key exchange, you can toss that key and try again. [0] https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem
btouellette 6y ago
Quantum communication isn't communication in the sense that you can decide what to send. You have a shared quantum state due to entanglement and you can guarantee that both sides see the same information when they observe the state but it's more like putting two identical messages into sealed envelopes and sending them off to be opened later (with the caveat that because the message hasn't been determined until it is observed you can prevent anyone from knowing what it is ahead of time). Much more detailed explanation here: https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-reasons-quantum-entanglement-doesnt-allow-faster-than-light-communication/#1882b3403a1e https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-r...
- attilakun 6y ago

soul4krsna 6y ago

Einstein read, studied and ate the Bhagavad-gita everyday. That's why his work is sound. Because the knowledge was revealed.

sidcool 6y ago

I did not get the point: "No useful information can be sent in quantum entanglement". Has it been found how entanglement actually works?

attilakun 6y ago
If you are familiar with probability theory, think of it like this: whatever you do with an entangled particle, it will never change other entangled particles' marginal probability, only the joint.
- da39a3ee 6y ago
  That's very helpful thanks, I do understand what that means but I didn't know I should/could think of entanglement like that.
thereisnospork 6y ago
An attempt at lay terms: imagine particles are tiny hands, and they can switch between being left hands and right hands. So to 'entangle' two particles is to make them shake. This means we now know that one particle is a lefty and the other a righty (two lefts can't shake each other) but because they are so small we don't know which is which. Now (gently) separate the two particles and place each in a box. It is presently unknown which is lefty, and which is righty so at this point each particle is considered to be in a superposition of both lefty and righty. A la Schrodingers cat each particle '''hasn't decided''' if it is a left or right. All QE states is that when we look in one box and see a right hand we know the other box contains a left hand - regardless of the distance between them. There is no provision or mechanism for shaking one particle and having a change occur with the other (information transfer).
- sidcool 6y ago
  That's a good explanation. However, since the particles are in superposition, the act of observation must be conveyed to the other particle, right?

segfaultbuserr 6y ago

> Well, the demon needs to have information about the motion of the atoms, otherwise it does not know when to open the door. The interesting thing about Maxwell’s demon is that it tells us entropy is somehow the opposite of information, you can use information to decrease entropy. It's the first connection between the laws of physics and the process of computing, although it's a modern reinterpretation (the original interpretation only argued measurements by the demon requires energy). An interesting implication is: all computers in this universe must generate heat because information is lost in the logic circuit. However, if we can construct the logic circuit in such a way that all information is preserved at the output (i.e. reversible) [0], this computer only needs an infinitesimal amount of energy to operate. Also a fun fact: Do you know that the term "daemon" for background processes was originally named after Maxwell's demon? [1] [0] https://en.wikipedia.org/wiki/Reversible_computing https://en.wikipedia.org/wiki/Reversible_computing [1] https://en.wikipedia.org/wiki/Daemon_(computing)#Terminology https://en.wikipedia.org/wiki/Daemon_(computing)#Terminology

bawana 6y ago

Sabine has made a name for herself being a contrarian. https://www.youtube.com/watch?v=sZI8-9i0SOo https://www.youtube.com/watch?v=sZI8-9i0SOo https://blogs.scientificamerican.com/cross-check/physicist-sabine-hossenfelder-fears-theorists-lacking-data-may-succumb-to-wishful-thinking/ https://blogs.scientificamerican.com/cross-check/physicist-s... She'll even take your money to answer your questions if you dont like physics forums https://www.aps.org/publications/apsnews/201611/hossenfelder.cfm https://www.aps.org/publications/apsnews/201611/hossenfelder... I dont mean to sound critical, but her statements remind me of Lord Kelvin's statement "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" Personally, I think theoretical physics should never be discussed in the absence of the specific data it is trying to address. So much confusion happens when the details are not understood first before the grand theory is proposed. Theories too often are presented as gifts from the heavens and without the corpus to which they speak.

platz 6y ago
- your initial comments are only ad-hominem - i don't think kelvin's statement represents her views - Being against a new collider does not mean one takes the position of Kelvin, or is anti-science. She doesn't argue against investment in novel science. Her argument is that a larger collider is the wrong kind of investment to make, based on what we've already observed at the LHC
dnautics 6y ago
> "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" It's not being critical, it's just a mischaracterization. I think that Sabine very much thinks there are new things to be discovered in physics, and she is taking an opinionated stance about what is the right way to get to them. > I think theoretical physics should never be discussed in the absence of the specific data it is trying to address. That's exactly what Sabine says.