Pure speculation, isn't the most interesting time period in the signal the transition from signal to no-signal (and back again)? How high is the resolution of the sensors? Is it possible that some frequencies are blocked fractionally earlier than others? At a fine enough temporal resolution, there might be more clues regarding the source.
Good question. For many FRBs there is access to the original antenna time streams (which are essentially voltages samples at 800 MHz), so superficially that might give you 1.25ns resolution. However, the intrinsic width of the pulses seem to be more like ~1ms. That tells you something about the emission source, giving you a rough upper bound on it's size of c * 1ms ~ 300km.
However, lots of interesting plasma physics effect occur between us and the FRB. The dominant thing that happens is that low frequencies arrive later than high frequencies (as they travel slow in a plasma). This causes the FRB to be smeared over many seconds rather than a millisecond. There's also multi path interference effects and an whole bunch of other stuff that happens. So actual the temporal structure of the burst tells you much more about the intervening medium than it does about the source.
A broader question that puzzles me, not specific to this phenomenon. Pulse length is often used to bound the size of a source in space (it cannot be smaller than light takes to traverse the object). But it’s possible that two phenomena can be correlated without being close, if there is a delayed action (akin to setting two alarm clocks and separating them in space). How can we confidently use this as evidence of size?
I guess the assumption is that the phenomenon starts at a point, spreads across the object sized l at c, and lasts for only a period of time t at any location. Therefore the pulse ends after l/c + t = T. By measuring T you can put an upper bound on l.
Example of this inference, from the Wikipedia on Fast Radio Bursts (but I have seen in many contexts):
> The sources are thought to be a few hundred kilometers or less in size, as the bursts last for only a few milliseconds
I think of multipath being about signals bouncing off other objects (reflection) and bending through media (refraction) before reaching the receiver. At the cosmic scale, I'm guessing multipath also involves gravitational lensing. Correct?
There is some possibility of gravitational lensing of FRBs and people are definitely searching for it. However, in this case it is refraction caused by variation in the density of the ionised gas between us and the source (within our galaxy, the host galaxy, and at lower densities in the intervening medium).
You just made me realize that it would be cheaper for an advanced civilization to send a message light years away by altering the medium through which the signal passes than to control the source directly, e.g. a neutron star.
This is a good question. FRBs pose a lot of challenges for follow up because most of them are not observed to repeat (this doesn't mean they don't repeat, just that they haven't been seen to). So you see them for a few seconds and then they're gone. To follow up, you need to know where exactly to look, and most of the instruments like CHIME used to discover FRBs don't have the resolution to see exactly where on the sky it was. You can maybe pin point it to within 1/4 degree, but need more like 1000th degree resolution to meaningfully follow up in other wavebands.
The most useful follow up has been for repeating FRBs. What happens there is that the discovery telescope tells you were it is roughly, and you know it repeats, so you can point a high resolution radio telescope (something like https://www.evlbi.org) to get a more precise location and then you can follow up with other telescopes.
One thing telescopes like CHIME are trying to do in the near future is to build their own long baseline station to give much higher resolution, such that they can get localisation on bursts which don't repeat, and do better follow up.
Thank you. I had been slightly familiar with fast follow up for SNs (that were detected optically), but their follow up times are much more forgiving than FRBs. The localization issue is also interesting.
I think astronomers often make it worse. I mean, we like thinking about why things are actually aliens as much as anyone else (LGM1 was already mentioned), and while we mostly try to restrain ourselves, every now and again a famous astronomer breaks and lets out a paper about it.
That's great to hear!
If some credible evidence of aliens did appear, where do you think it would come from? Tabby's Star like data? atmospheric spectra? FRB's? other?
Would absolutely love to hear your thoughts :)
That already happened. Living cells are nanotechnology. Something loaded with them impacted billions of years ago, and we're currently working on AI and rockets.
Make yourself intra-universally interesting enough that the alien construction management AI might instantiate a simulation of you from the cached info at some point. It's a strange sort of Darwinism, but it's all we've got.
I think there was a HN thread not that long ago about speculation that (at least some) viruses come to earth from space, so perhaps it is happening all the time.
This seems such a "flat earth" type of hypothesis. I mean viruses depend on their hosts 100% so them coming from somewhere with no hosts and successfully slotting in with new hosts just seems immeasurably unlikely.
Imagine you're arbitrarily close to the physical limits of technology. You do or could understand how living things work, down to the molecular level, for example, and know how to engineer self-replicating machinery analogous to DNA. At the very least, you could build a 'spaceship' that can grow something at least as efficient as people, who can replicate however and disassemble earth for raw materials. Presumably, you can do much better, and you end up with something like a self-packaged deployable technological superintelligent ecosystem.
I haven't seen the original paper (maybe that should've been linked instead?), but the MIT press release is dripping with "Not it's saying aliens..." innuendo.
It's kind of hypocritical to use nod-wink-aliens-clickbait to drum up media attention, then ridicule the first rube who asks if aliens could possibly be involved.
That's a fair comment. I mostly think the MIT press release is pretty good and doesn't go down that route, except for the title, which is definitely hinting at it.
Also agree that it would make sense to replace the link with the actual paper, or an article about it. University press releases are mostly there to play up their own contribution.
I'm not super involved on the FRB side of CHIME, so I'm not 100% clear what is public and what isn't. But you can an idea from public info around the internet. I think the last total number made public was over 700 in March this year, and the previous one 30 in October 2018 (https://aasnova.org/2020/03/13/chime-detects-even-more-repea...).
Yeah, that's definitely one of the main hypotheses. There aren't any other repeating FRBs known to do this yet, so how general a mechanism this is, is not known.
In order to maximize impact. Press doesn't want to talk about this unless there is an embargo, otherwise they might be 'late' in which case they would rather not mention it at all (and not have to spend costly journalist time)
The more powerful technology provides the more powerful chips and telescopes and microscopes. On the basis of new data obtained with the help of new devices, new theories are created that help in creating even more microscopic components, which will help in creating even more powerful devices recursively. The singularity in the action of CHIME and AI made it possible to determine the signal; a major breakthrough is coming in all areas. Interestingly, somewhere there is a miscalculation when we can look into the space using a smartphone in real time? Any related theorems?
Assuming that it is aliens, for a moment, we can not know if these aliens are friendly or hostile, right? So, given that there is a 50/50 chance of them being hostile, and given their awesome show of strength, the precautionary principal dictates that we not advertise our presence too loudly.
They wouldn't know about us for 500 million years, assuming we could emit a strong enough signal for them to detect that far away. Any aliens that could actually pose a threat would probably be close enough to pick up our emissions anyway.