---
title: 'Physicists Say It''s Possible to Send Messages to the Past'
source: 'https://youtube.com/watch?v=RZrHrw1ubqs'
video_id: 'RZrHrw1ubqs'
date: 2026-08-04
duration_sec: 381
---

# Physicists Say It's Possible to Send Messages to the Past

> Source: [Physicists Say It's Possible to Send Messages to the Past](https://youtube.com/watch?v=RZrHrw1ubqs)

## Summary

This video discusses a theoretical physics paper published in PRL that suggests a new method for sending messages into the past using quantum mechanics. The presenter explains the concept, its limitations, and why it might not be as revolutionary as headlines suggest.

### Key Points

- **Headlines Claim Time Messaging** [00:00] — Headlines claim physicists have figured out a new way to send messages into the past, based on a paper in PRL.
- **Theoretical Study, Not Practical** [00:29] — The study is theoretical and does not involve DeLoreans or black holes; it requires quantum physics.
- **Quantum Physics and Causality** [00:42] — Quantum physics has an uneasy relation with causality because particles can do multiple things at once, and there's no objective way to tell what happens at the same time, making causality uncertain.
- **The Scenario** [01:14] — The paper from MIT involves a receiver device built at some time, a special quantum state prepared, and a sender who measures the state to inject information into the past.
- **Noise is Less Problematic** [02:01] — The new paper shows that noise in the communication channel is less of a problem for sending messages into the past than into the future.
- **Postselection** [02:32] — They use postselection, meaning after measuring the quantum state, they only look at specific outcomes, postulating a universe with only one outcome.
- **Prediction vs. Time Message** [03:00] — The key point is that you can't tell apart a message from the future from a prediction; both are indistinguishable.
- **Practical Impossibility** [03:43] — In reality, we can't predict quantum outcomes, and postselection isn't enforceable, so the device works like posting many predictions and deleting all but the correct one.
- **Bullshit Meter Rating** [04:32] — The presenter rates the paper 8 out of 10 on the bullshit meter, noting the maths works but the interpretation is questionable.
- **Real Story: Rethinking Temporal Relations** [04:45] — The real story is that physicists are rethinking temporal relations, which are more complicated than simple cause-effect.

### Conclusion

The video concludes that while the paper is mathematically sound, its interpretation is questionable, and the real significance lies in physicists rethinking causality and temporal relations.

## Transcript

Sending messages into the past just got easier.  Or, as the headlines put it “We have figured out   a new way to send messages into the past”  and “Physicists Say It’s Possible to Send  
Messages Backward in Time”. Even more  amazing, these headlines are based on   a paper published in PRL, the top journal  in the field. As you’ve guessed correctly,   no one’s yet figured out how to actually send  messages into the past, this is a theoretical  
study. But it’s quite interesting indeed, and no  it does not involve a DeLorean, a time fairy, or a   black hole behind a bookshelf. It just requires a  little bit of quantum physics. Let’s have a look.
Quantum physics has an uneasy relation  with causality. This is because once   you accept that particles can do  multiple things at the same time,   and factor in that Einstein tells us there  is no objective way to tell what happens at  
the same time, then quantum mechanics also  tells you that generally you can’t tell what   happened in which order. Causality becomes  as uncertain as the rest of quantum physics.  And of course the first question you might have  is: can I make money with it? Who wouldn’t want  
to tell their younger self to buy Nvidia stocks  without having to grow a wormhole in the basement! The new paper is a continuation of an earlier  work. It comes from an MIT group and the scenario  
they look at is loosely speaking this. You  have a receiver device that you have built at   some time and that is ready to receive messages  from the future. Before you build the device,   you can’t get any messages. Then you have  a special quantum state that you prepare  
and you let it do its quantum thing. And  once the quantum state has done its thing,   there is a sender who measures the quantum  state and that, so the idea injects   information in the message receiver in the past. In the new paper they show that this still works  
if there is noise in this communication channel.  Amazingly enough, if you want to send messages   into the past, the noise is less of a problem  than if you want to send it into the future.
referring to a future work from 1985  co-authored by E L Brown and M McFly. Ok, but leaving aside the noise, just what do they  say we must do to send messages into the past?  
They are using what is called “postselection”.  This basically means that after you have done   the measurement of the quantum state,  you only look at specific outcomes. You see, in quantum physics we cannot  normally predict the outcome of the  
experiment. But they postulate that we  basically live in a universe with only   one outcome. And then the message that you get  in the past is… the outcome which will happen.
Ok, but wait, how is this not just making a  prediction? Well, to me this is the key point   of the paper: in general you can’t tell these  two things apart. Forget the quantum stuff for  
a moment, imagine that you just sit there with  your device that can receive messages from the   future… or so you think. It has a screen and  noise flickers on the screen most of the time,   then suddenly it says “BUY NVIDIA”. You go  buy Nvidia and a year later you’re rich.  
But did you get a message from the  future or is your machine just good   at predicting the stock market? There is  no way to tell these two things apart. I don’t know about you, but if I had such  a device I wouldn’t care. Physicists could  
discuss until the end of time whether  it really does receive messages from the   future or whether it’s just crazy good at making  predictions. I'll be sitting at the pool, cheers.  That said, in today’s reality we  can’t predict the outcome of quantum  
measurements and post-selection isn’t  something you can magically enforce on   our universe. This means that for practical  purposes their device works more like this: Suppose I set up an X-twitter account and post  a hundred thousand messages predicting the next  
major LA earthquake for any possible day until  2100. Then, once it happens, I delete all messages   but one, celebrate the correct prediction  and claim that it was given to me by a time  
traveller. Works on X, doesn’t work in reality. So I have to give this paper a 8 out of 10 on   the bullshit meter. The maths works out, but their  interpretation is highly questionable. That said,  
the real story here isn’t that physicists have  invented a working telephone to yesterday.   The story is that physicists are slowly  rethinking temporal relations which I  
think are much more complicated than the  simple cause-effect idea that we’re used to. I promise I’ll have a word with my past  self about questionable hairstyle choices.
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