• Member Since 28th Oct, 2012
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Particle Physics and Pony Fiction Experimentalist

More Blog Posts417

  • 3 weeks
    Constitutional monarchies

    Yesterday, I had an extra day’s holiday, thanks to the King choosing this weekend to get crowned. This has caused all sorts of admin problems, as he decided to do so in the middle of a busy university term, but it meant I had a bit of time to write a short blog post. Apologies for not writing anything for the last two months. I have been busy doing various complicated, and mostly boring, particle

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    9 comments · 188 views
  • 15 weeks
    Lepton Flavour Universality

    It must be time for me to write another particle physics blog post, telling a story from the quest to find new scientific phenomena and resolve the mysteries of the universe. With pictures of ponies. So here we go. Prepare to learn all about Lepton Flavour Universality. To enhance your blog reading experience, first go and get a smoothie.

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    19 comments · 227 views
  • 17 weeks
    Hearts and Hooves and Carnivorous Plants

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    3 comments · 200 views
  • 21 weeks
    Pinkie’s Antimatter Adventure; Rainbow Magic – Writing pony science stories with Chat GPT

    Yesterday I decided to investigate this Chat GPT thing that I now hear so much about. And wow—this technology has really moved on since I last looked at it. We now have an AI engine which, given a simple prompt, will write a story for you in seconds.

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    22 comments · 364 views
  • 23 weeks
    Wishing Star Scouting

    At this time of year, there is a tradition of planetarium shows about possible astronomical explanations for the story of the Star of Bethlehem, which guided the Magi to the baby Jesus. Scholars have been pondering this for centuries. It’s a fun question to ponder as it mixes biblical scripture, history, astrophysics, and lets us talk about comets, novae, supernovae, planetary conjunctions, along

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    5 comments · 187 views

Time travel in Equestria and other universes · 12:19am Jan 19th, 2015

Following last week's post about the lesson on special relativity which we received in It's About Time, I started to think about what this episode tells us about time travel in Equestria?

What do we know about time travel in our own universe?

Not a great deal. Travelling forwards in time is straightforward—we do it all the time—and we know from special relativity, that if we could travel close to the speed of light, we could, in effect, journey into the future.

But travelling backwards in time is a whole different kettle of fish. This has the potential to make so many problems that it seems rather likely that it is impossible. But no one has been able to produce a robust proof that this is so, as there may be ways to get around the inherent paradoxes. There are some speculative designs for time machines. Unfortunately all of them seem to have flaws, they would only allow travel back to times after the machine was created, and in any case, would require some somewhat unrealistic engineering—creating wormholes and such like.

First we have the potential for causality violation—or the grandfather paradox. Given a time machine, you could, in theory, go back in time and kill your grandfather before you were born. But then you would never have been born—so you couldn't go back in time, and grandad is safe—except that would mean you would be born... It's not scientifically possible!

This doesn't necessarily mean travelling back in time is impossible, as there might be something else which prevents such a logical inconsistency. This is what happens in It's About Time. For all Twilight's efforts to alter events, she just ends up creating the very thing which set her off on the adventure. This approach has produced some of the best time travel fiction, as it ties up the plot nicely. No violation of causality. It does require a rather restricted type of time travel (hence the spell could only be used once.)

But It's About Time is not paradox-free as it does appear to violate the conservation of information. Twilight learns from her future self that the time spells are in the Starswirl the Bearded wing of the Canterlot Archive. And then goes back in time to pass on the information to herself. So where did this knowledge come from?

Or consider this scenario: if I could create a tiny wormhole in my lab, just big enough to pass a radio signal, I could connect my laptop to the future wifi network, go to fimfiction and download all the stories which I will have submitted by that point in the future. Then I wouldn't have to go to the trouble of writing them as I could just log onto the past fimfiction and upload them. But if I didn't write them? Who did?

A way around this, and also the causality problem, might be possible through the idea of parallel universes. This way, if you travel back in time and mess things up, it will change the future in a parallel future, not the one you came from. And while a story must be written from scratch in one universe, it could then be to sent back in time in a different one, and recycled as much as you like.

If this is true in Equestria, then it would suggest that there must be a story to explain how the loop which Twilight created in It's About Time got started.

Comments ( 10 )

Was trying to remember the mind breaking experiment I saw a while back.

Looking back in time.

So far, 8 nanoseconds. Im wondering if anyone has tried adding kilometers of fibre optic cable, then manipulating the various detectors to see if information can be transmitted.

Thing is, if you consider quantum mechanics as a whole, it is very non tme like, fully symetrical etc. That is, all information exists at all points in space and time in superposition, you just extract a statistical peak on averaging. But, you never perfectly remove other effects. If you manage to make a quantum selection to a plank length, it will ony be for a plank time, then the next length will bi a different time.

Why cant positive feedback closed time loops be valid? Two examples Ive seen proposed, are that of matter,antimatter virtual particle pairs, and the other, being the universe.

If this is true in Equestria, then it would suggest that there must be a story to explain how the loop which Twilight created in It's About Time got started.

There sure is. That's just one possibility, though, and a little rough around the edges. (Would Twilight notice very small differences between the trip she saw as Past Twilight and the one she saw as Future Twilight? Such things could compound through the repetitions of the loop.)

The Man Who Murdered Mohammed by Alfred Bester is a great look at what happens when you go back in time and try to alter the past.

Ooh, and it's by Eakin, who made a point of pretending I didn't exist at BronyCon! (not that I blame him)
<commences to read>

I've always favored the parallel timelines approach. After all, you change the past just by going there, because in your native timeline, you weren't there then. Unless, of course, you were, in which case it might be possible to cause a paradox through inaction. :unsuresweetie:

¡Eakin already wrote a story explaining the inception of the timeloop in “It’s About Time”!:


Information paradoxes are bad.
If "information" is replaced with "physical object", the object ages to infinity in a matter of moments.


There is a limit to hw fast smethng can age, lose infomation.

Hawking Radiation. Rate of information loss from a black hole. But this should be a limt, there should also be a lesser bidirectional energy flow from lesser gravity fields, maybe thats what another description for foam is, or even time?

My point on the aging thing is if an object is sent back in time, and then given to your past self, the object has no beginning or end. You can't know (unless an outsider tells you) which time loop number you're on. Therefore, either the object can't age, or it has already turned to dust, or it implodes.


There is something related to this. Time crystals. A currently theoretical construct where the quantum mechanics solution is stable in the temporal axis. Also, you are thinking that information is being created from nothing. If we take the rule that information cannot be created or destroyed, which was teh problem Hawking worked on for black holes, then coming accross something in a closed time lopp in the future, doesnt mean the information has been created out of nothing, it implies that the information has always existed, we just havent got to it yet.

this is the paradox between in universe relativistic observation, and out of universe quantum mechanical observation. Attempting to make in universe quantum mechanical observations, makes the observer part of the quantum mechanical interaction. And scientists hate not being god.

Apparently there is an article in the Scientific American magazine, about how to mmake such a delayed choice experiment at home, using polarising filters. My favourite is to use microwave radiation, ebcause its long eough wavelength to be manually altered, and can be easily generated by Bluetooth and Wifi, where I was looking at it first in the 80s, didnt like to try, because microwave ovens are dangerous.

Hmm, Crossing the Michaelson Morely interferometer with delayed choice.Thic could be intresting.

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