Search FQXi

If you are aware of an interesting new academic paper (that has been published in a peer-reviewed journal or has appeared on the arXiv), a conference talk (at an official professional scientific meeting), an external blog post (by a professional scientist) or a news item (in the mainstream news media), which you think might make an interesting topic for an FQXi blog post, then please contact us at with a link to the original source and a sentence about why you think that the work is worthy of discussion. Please note that we receive many such suggestions and while we endeavour to respond to them, we may not be able to reply to all suggestions.

Please also note that we do not accept unsolicited posts and we cannot review, or open new threads for, unsolicited articles or papers. Requests to review or post such materials will not be answered. If you have your own novel physics theory or model, which you would like to post for further discussion among then FQXi community, then please add them directly to the "Alternative Models of Reality" thread, or to the "Alternative Models of Cosmology" thread. Thank you.

Contests Home

Current Essay Contest

Previous Contests

Wandering Towards a Goal
How can mindless mathematical laws give rise to aims and intention?
December 2, 2016 to March 3, 2017
Contest Partner: The Peter and Patricia Gruber Fund.

Trick or Truth: The Mysterious Connection Between Physics and Mathematics
Contest Partners: Nanotronics Imaging, The Peter and Patricia Gruber Foundation, and The John Templeton Foundation
Media Partner: Scientific American


How Should Humanity Steer the Future?
January 9, 2014 - August 31, 2014
Contest Partners: Jaan Tallinn, The Peter and Patricia Gruber Foundation, The John Templeton Foundation, and Scientific American

It From Bit or Bit From It
March 25 - June 28, 2013
Contest Partners: The Gruber Foundation, J. Templeton Foundation, and Scientific American

Questioning the Foundations
Which of Our Basic Physical Assumptions Are Wrong?
May 24 - August 31, 2012
Contest Partners: The Peter and Patricia Gruber Foundation, SubMeta, and Scientific American

Is Reality Digital or Analog?
November 2010 - February 2011
Contest Partners: The Peter and Patricia Gruber Foundation and Scientific American

What's Ultimately Possible in Physics?
May - October 2009
Contest Partners: Astrid and Bruce McWilliams

The Nature of Time
August - December 2008

Forum Home
Terms of Use

Order posts by:
 chronological order
 most recent first

Posts by the author are highlighted in orange; posts by FQXi Members are highlighted in blue.

By using the FQXi Forum, you acknowledge reading and agree to abide by the Terms of Use

 RSS feed | RSS help


John Merryman: "The problem is that we do experience reality as those discrete flashes of..." in The Quantum...

Thomas Ray: "(reposted in correct thread) Lorraine, Nah. That's nothing like my view...." in 2015 in Review: New...

Lorraine Ford: "Clearly “law-of-nature” relationships and associated numbers represent..." in Physics of the Observer -...

Lee Bloomquist: "Information Channel. An example from Jon Barwise. At the workshop..." in Physics of the Observer -...

Lee Bloomquist: "Please clarify. I just tried to put a simple model of an observer in the..." in Alternative Models of...

Lee Bloomquist: "Footnote...for the above post, the one with the equation existence =..." in Alternative Models of...

Thomas Ray: "In fact, symmetry is the most pervasive physical principle that exists. ..." in “Spookiness”...

Thomas Ray: "It's easy to get wound around the axle with black hole thermodynamics,..." in “Spookiness”...

click titles to read articles

Why Time Might Not Be an Illusion
Einstein’s relativity pushes physicists towards a picture of the universe as a block, in which the past, present, and future all exist on the same footing; but maybe that shift in thinking has gone too far.

The Complexity Conundrum
Resolving the black hole firewall paradox—by calculating what a real astronaut would compute at the black hole's edge.

Quantum Dream Time
Defining a ‘quantum clock’ and a 'quantum ruler' could help those attempting to unify physics—and solve the mystery of vanishing time.

Our Place in the Multiverse
Calculating the odds that intelligent observers arise in parallel universes—and working out what they might see.

Sounding the Drums to Listen for Gravity’s Effect on Quantum Phenomena
A bench-top experiment could test the notion that gravity breaks delicate quantum superpositions.

March 17, 2018

CATEGORY: The Nature of Time Essay Contest (2008) [back]
TOPIC: On the global existence of time by Ettore Minguzzi [refresh]
Bookmark and Share
Login or create account to post reply or comment.

Ettore Minguzzi wrote on Oct. 13, 2008 @ 09:42 GMT
Essay Abstract

The existence of a global time is often taken for granted but should instead be considered as a matter of investigation. By using the tools of global Lorentzian geometry I prove that, under physically reasonable conditions, the impossibility of finding a global time implies the singularity of spacetime.

Author Bio

Ettore Minguzzi is researcher of mathematical physics at the University of Florence, Italy. He has earned his PhD from Milano University in 2002. His main research interests are in general relativity and applied gauge theories. In the last years he has contributed to global Lorentzian geometry and causality theory in particular with the study of the "causal ladder of spacetimes". He is a member of SIGRAV "Società Italiana di Relatività Generale e Fisica della Gravitazione", SEGRE "Spanish Society on Relativity and Gravitation" and ISGRG "International Society on General Relativity and Gravitation".

Download Essay PDF File

Bookmark and Share

Ettore Minguzzi wrote on Dec. 1, 2008 @ 11:45 GMT
I inform the readers that recently, the technical papers on which this essay is based, namely reference [13] "Chronological spacetimes without lightlike lines are stably

causal" and [14] "K-causality coincides with stable causality" have received positive referee reports from Communications in Mathematical Physics (minor changes have been asked).

Bookmark and Share

Cristi Stoica wrote on Dec. 6, 2008 @ 12:03 GMT
Dear Dr. Minguzzi,

I read your essay, which I consider impressive, as it shows that in a Lorentz manifold the existence of singularities can be guaranteed under more relaxed circumstances than usual. I find interesting your main result concerning the existence of singularities in the absence of a global time without closed causal curves.

Best wishes,

Cristi Stoica

“Flowing with a Frozen River”,

Bookmark and Share

Ettore wrote on Dec. 6, 2008 @ 15:45 GMT
Thank you for the appreciation Cristi, it is nice to receive some feedback. Ettore

Bookmark and Share

Ettore Minguzzi wrote on Dec. 23, 2008 @ 13:43 GMT
References [13] and [14] have now been accepted for publication in CMP.

Bookmark and Share

Dimi Chakalov wrote on Dec. 26, 2008 @ 02:31 GMT
Dear Dr. Minguzzi,

Reading your Essay is a joy. You have this utterly professional skills to elaborate on the most intricate issues in GR -- the obvious, and deeply puzzling, fact that we observe mass with one "charge" only.

May I ask a question. You wrote: "Instead, only massless particles make sense, and thus the concept of non-singularity must be expressed from the ‘point of view’ of massless particles."

I wonder how you would explain the absence of Closed Timelike Curves (CTCs) from the ‘point of view’ of massless particles. CTCs are exactly what we should expect from GR (cf. W.B. Bonnor, Closed timelike curves in general relativity, Int. J. Mod. Phys. D12 (2003) 1705-1708; gr-qc/0211051 v1). It seems to me that CTCs (and timelike naked singularities, cf. R. Goswami et al., gr-qc/0410041v1) are just like the ultraviolet catastrophe from 1905, which too has never happened.

Thank you for your (global) time.

Dimi Chakalov

Bookmark and Share

Ettore Minguzzi wrote on Dec. 28, 2008 @ 13:59 GMT
Dear Dr. Chakalov,

thank you for the appreciation and feedback.

My opinion is that spacetimes with chronology violating regions (CTC) are worth studying and should not be dismissed a priori. Nevertheless, in this work I assume that the absence of CTC could be physically justified at least in some limit. In reference [13] I considered the case in which the spacetime admits CTC. Thanks to a result due to Kriele, the main conclusion of my work does not change if the chronology violating region is of limited size (i.e. does not extend to infinity). It is sometimes speculated that future civilizations could perhaps produce chronology violating regions but in this case these regions would probably be limited (time machines). Thus in this case the consequences of the main theorem (i.e. the existence of a time function under null geodesic completeness) would still hold.

As for the presence of timelike naked singularity, their possible presence does not change the main result of this work since the cosmic censorship conjecture is not assumed. Indeed, assuming it for instance in the strong form would be equivalent to the assumption of global hyperbolicity which implies stable causality and hence the existence of a time function. Clearly, in this case it would be trivial to deduce the existence of a time function.

Best wishes,

E. Minguzzi

Bookmark and Share

Dimi Chakalov wrote on Dec. 28, 2008 @ 20:50 GMT
Regarding CTCs: I believe it was proven that any locally reflecting spacetime with a CTC is 'totally vicious', i.e. one with a CTC through every point (Jong-Chul Kim and Jin-Hwan Kim, Totally vicious space-times, J Math Phys 34 (1993) 2435-2439). A CTC is worse than the Ebola virus, as it is interwoven in the possible models of spacetimes permitted in GR. Yet there is no trace from any CTCs in the Cosmic Microwave Background Radiation. No trace from any timelike naked singularity either. Ergo, we might be facing the kind of "ultraviolet catastrophe" I mentioned before, and need some really huge breakthrough to explain why all these nasty things have never happened.

I wish you best of luck with your work.

Dimi Chakalov

Bookmark and Share

Jane Smith wrote on Jul. 12, 2017 @ 08:00 GMT
Nice looking sites and great work. Pretty nice information. It has a better understanding. Thanks for spending time on it. survival games

Bookmark and Share
report post as inappropriate

yify tv tv wrote on Mar. 7, 2018 @ 09:48 GMT
Thanks for sharing.I hope you continue to have such quality articles to share with everyone! I believe there will be many people who share my views when they read this article from you!

- yify

Bookmark and Share
report post as inappropriate

Login or create account to post reply or comment.

Please enter your e-mail address:
Note: Joining the FQXi mailing list does not give you a login account or constitute membership in the organization.