tag:blogger.com,1999:blog-22973357.post7284773887472388123..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Dear Dr. B: What do physicists mean when they say time doesn’t exist?Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger34125tag:blogger.com,1999:blog-22973357.post-68921293462564737802016-12-16T00:53:18.095-05:002016-12-16T00:53:18.095-05:00Time is a coordinate of a differentiable space-tim...Time is a coordinate of a differentiable space-time manifold with Lorentzian signature. It's the one with the odd signature out, depending on convention that's either plus or minus. That's the definition. You can't define time as the thing that a clock reads because for that you'd first have to define what a clock is. Once you introduce matter, you can define a clock and you&#Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20235777484156542022016-12-15T22:55:09.478-05:002016-12-15T22:55:09.478-05:00Sabine: You say that "time is real in a well-...Sabine: You say that "time is real in a well-defined way" -- So, what is that definition of time that you mention? All I can find is, <b><i>"Time in physics is defined by its measurement: time is what a clock reads."</i></b> (en.wikipedia.org/wiki/Time_in_physics) Can you help me out, please?Henry Normanhttps://www.blogger.com/profile/07818971016888907427noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18001503317478688972016-12-07T12:24:14.392-05:002016-12-07T12:24:14.392-05:00Slight tangent to your post. Well, I guess it'...Slight tangent to your post. Well, I guess it's coming at the nature of time from a different direction.<br /><br />Specifically, I'm thinking of Aharonov's and Tollaksen's Time Symmetric Quantum Mechanics (TSQM). I've been following this theory for a little over 10 years now. At first, it didn't seem very popular. But, it seems like lately it's gaining some groundAnonymoushttps://www.blogger.com/profile/02260017465845457855noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-40867214142050307622015-11-15T11:12:04.545-05:002015-11-15T11:12:04.545-05:00@George
Well I haven't read your book so I...@George<br /><br />Well I haven't read your book so I've no idea what your argument is but it's implausible to me that one exists that would support your claim. Copenhagists and QBists don't only argue for their interpretations by poking holes in other interpretations. Once you've interpreted QT as, fundamentally, the application of (non-commutative, 'subjective') Paul Hayeshttps://www.blogger.com/profile/04309125585593320043noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81259200022242648742015-11-15T02:25:51.240-05:002015-11-15T02:25:51.240-05:00George,
I have always made it clear that it's...George,<br /><br />I have always made it clear that it's perfectly fine by me to say that free will is emergent - a forest made of trees. The problem is that people want it to be a forest that isn't made of trees, and last time I looked you were one of these "people". I somehow lost track of this, sorry. I will come back to it eventually... Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-50532058073733893012015-11-12T14:09:13.583-05:002015-11-12T14:09:13.583-05:00Ok Sabine, i've read your expose, it is very i...Ok Sabine, i've read your expose, it is very informative and didactic, thank you.<br />The following is rather a long paragraph, but i hope you will take the time to look into it.<br />I'm trying to get a grasp of this 'time' by hypothetically putting myself at a spot outside of the universe, to get an understanding as a non-participant so to speak. Taking the phylosophical Koenraad Van Spaendonckhttps://www.blogger.com/profile/15090279727324831109noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22121222969221973522015-11-12T13:13:45.017-05:002015-11-12T13:13:45.017-05:00Ok, thank you.Ok, thank you.Koenraad Van Spaendonckhttps://www.blogger.com/profile/15090279727324831109noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83817216301101414802015-11-12T12:57:24.024-05:002015-11-12T12:57:24.024-05:00@Mike The past 45 years of non-classical gravitat...@Mike The past 45 years of non-classical gravitation summed are non-empirical - assuming the Equivalence Principle (Einstein's elevators). Given Newton's assumptions, where is GR, QM, and stat mech? Derivation cannot detect weak postulates. Crackpot Bolyai said a triangle's three interior angles can sum to other than Euclidean 180 degrees, like 300+ degrees,<br /><br />71.295556 Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89894601046004186992015-11-12T12:56:27.619-05:002015-11-12T12:56:27.619-05:00"buy-the-book"
A real rarity: too many ...<i>"buy-the-book"</i><br /><br />A real rarity: too many hyphens!<br />Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33767281132000266882015-11-12T12:37:41.311-05:002015-11-12T12:37:41.311-05:00Some thoughts on time;
We experience reality as f...Some thoughts on time;<br /> We experience reality as flashes of cognition and so think of time as the point of the present moving from past to future events. Physics essentially codifies this by treating it as measures of duration, from one event to the next.<br /> The basic reality though, is that it is a changing configuration creating and dissolving these events, such that they go future to John Merrymanhttps://www.blogger.com/profile/15106596586767479118noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-40421015336345776812015-11-12T12:21:45.035-05:002015-11-12T12:21:45.035-05:00Hi Noa,
I explained this several years ago here. ...Hi Noa,<br /><br /><a href="http://backreaction.blogspot.com/2008/05/block-universe.html" rel="nofollow">I explained this several years ago here</a>. Looking at this now, I'm not sure how comprehensible it is, but give it a try. If that doesn't help, I'll give it another go ;) Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86839574106770462482015-11-12T12:14:48.407-05:002015-11-12T12:14:48.407-05:00Hello Sabine,
In your explanations above you say ...Hello Sabine,<br /><br />In your explanations above you say : "In this view, every moment in time exists in some way."<br />Can you explain how this conclusion is reached, starting from the GR definition of time, where time is what clocks measure. We could indeed observe many clocks, each at for instance a different radius from the earth, and notice that they each will indicate a Koenraad Van Spaendonckhttps://www.blogger.com/profile/15090279727324831109noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-21727614024162655962015-11-12T10:16:36.679-05:002015-11-12T10:16:36.679-05:00Mike,
I have honestly no clue what you are talkin...Mike,<br /><br />I have honestly no clue what you are talking about. All that I am trying to say is: If you want to understand what Lee says, you should read his book, and not listen to me. If you found it "easy to understand," then I am curious to hear what you think he means with "time being real." If you think he means the same as I mean, then I think you misunderstood Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39845728833092071302015-11-12T09:25:46.412-05:002015-11-12T09:25:46.412-05:00Dear Sabine,
After thinking it over, I do wish to...Dear Sabine, <br />After thinking it over, I do wish to say I don't believe your attitude befits someone who very clearly wishes to be taken seriously. I am hoping sincerely that you might come around to agree with me.<br /><br />I came to your blog last night from Motl's. He had used your name in an offhanded way to characterize something as easy to understand while also making a Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39071812640315548782015-11-12T07:25:34.273-05:002015-11-12T07:25:34.273-05:00From what I can see of George Musser's book co...From what I can see of George Musser's book courtesy of Amazon.com it looks like it's mostly (or even all) psiontology. He says, "in the case of nonlocality, even the most die-hard skeptic accepts that something very weird is going on, something that forces us to go beyond our deepest-held notions of space and time." Really? So where does that leave the <a href="http://Paul Hayeshttps://www.blogger.com/profile/04309125585593320043noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-8904585387948471112015-11-12T02:35:26.042-05:002015-11-12T02:35:26.042-05:00Thanks SabineThanks SabineWaterbergshttps://www.blogger.com/profile/17079354080799783939noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-36925829710376508842015-11-12T02:00:58.549-05:002015-11-12T02:00:58.549-05:00Sean Carroll's lecture notes are a good start....<a href="http://preposterousuniverse.com/grnotes/" rel="nofollow">Sean Carroll's lecture notes</a> are a good start. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-84550137633536524602015-11-12T01:44:29.035-05:002015-11-12T01:44:29.035-05:00Thanks Sabine. Can you recommend a online resource...Thanks Sabine. Can you recommend a online resource that provides a good introduction to General Relativity for someone with a science background who isn't afraid of maths?Waterbergshttps://www.blogger.com/profile/17079354080799783939noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18309908561174277162015-11-12T00:16:02.779-05:002015-11-12T00:16:02.779-05:00Waterberg,
It's an extract from his book (whi...Waterberg,<br /><br />It's an extract from his book (which I mentioned above). I took the sentence you quote to mean that in the Newtonian limit it's only the tt-component of the metric that enters, so in that interpretation it's correct. Roughly speaking, the reason is that every contribution from a space-coordinate is suppressed by v/c which, for objects we deal with, is always <Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-87759629651989284282015-11-11T12:33:03.983-05:002015-11-11T12:33:03.983-05:00Slightly off topic, but George Musser has an artic...Slightly off topic, but George Musser has an article in SciAm on nonlocality (I presume to promote his book that you reviewed):<br /><br />http://www.scientificamerican.com/article/how-einstein-revealed-the-universe-s-strange-nonlocality/<br /><br />He claims that objects fall "because Earth's mass warps time. The warping of space plays only a minor role in these cases"<br /><br />Waterbergshttps://www.blogger.com/profile/17079354080799783939noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9580682009232057212015-11-11T11:48:12.842-05:002015-11-11T11:48:12.842-05:00Michael,
An excellent question! Speaking of an &q...Michael,<br /><br />An excellent question! Speaking of an "instantaneous correlation" doesn't make sense. The particles are correlated, period. It is correct that it "looks like" a contradiction to SR. But it isn't. There isn't anything observable in this description that contradicts SR. Yes, some people don't like the "instantaneous" collapse, but itSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71613308243643023202015-11-11T11:33:17.402-05:002015-11-11T11:33:17.402-05:00Can you explain more about the concept of time as ...Can you explain more about the concept of time as it relates to quantum entanglement? If one particle of an entangled pair is distant, accelerating away, and in the neighborhood of a gravity well, isn't it hard to synchronize time between the two particles so that an "instantaneous" correlation between the particles makes any sense as a concept.<br /><br />To my layman's Michael Mussonhttps://www.blogger.com/profile/17360143418083381579noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11184091067442724472015-11-11T06:50:24.992-05:002015-11-11T06:50:24.992-05:00Giotis,
I was thinking that would be too technica...Giotis,<br /><br />I was thinking that would be too technical. In my perspective this "problem of time" merely means, as in classical GR, that one has to pick a time coordinate by hand, or use one that is defined from the flow of some matter field. I don't really understand why this is a problem. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75486038648528899722015-11-11T02:17:06.440-05:002015-11-11T02:17:06.440-05:00What about the Wheeler-DeWitt equation and the fac...What about the Wheeler-DeWitt equation and the fact that time evolution is a Hamiltionian constraint(HΨ=0)? People often begin discussion regarding the "problem of time" by referring to this.Giotishttps://www.blogger.com/profile/01538762241438887298noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-26332298439633052632015-11-10T12:39:44.210-05:002015-11-10T12:39:44.210-05:00Here's my take on it : There are (at least) 2 ...Here's my take on it : There are (at least) 2 interpretations of time. We can't remember the future because it hasn't happened yet. We can remember the past because is has happened. That's how we experience time in an absolute way. Then there's time in Relativity. The most general description of time here is : Time is what clocks measure. Mixing those 2 notions of time leads Koenraad Van Spaendonckhttps://www.blogger.com/profile/15090279727324831109noreply@blogger.com