How does a team operate in a situation of one-way communication?

Question

So I had a lot of fun reading the short story "Into Darkness" written by Greg Egan (Axiomatic 2010). I want to play with a few of the concepts of that story. In particular, the general theme of a rescue crew going in to assist in the face of some event where the precise nature of what is going on is poorly understood.

In "Into Darkness" there are randomly occurring events that take place, which I am going to refer to as Anistropic events. From the outside it looks like a giant completely black hemi-sphere suddenly appears. It projects around from a point, with a radius covering up to a couple of city blocks, though the limits on the size are poorly understood. The event appears black from the outside because light does not pass through it, or reflect off it's boundary.

Inside the event, time becomes bound to the spatial dimension projecting from the center around the radius. That is time only moves forward as you move closer to the center. To an observer inside the event, they can see rays of light from outside (the past) but none projecting back from inside. They can move along an arc, or in a line towards the center. But they cannot move away from the center. In Egan's story, surviving an event like this requires one to travel to it's epi-center. After a period of unknown time the event passes, and all matter outside the epi-centre is homogenized. So "runners" volunteer to run in and guide any unlucky folk to the epi-centre.

Naturally this impacts the communications available to the rescue team. If I recall correctly, the ones entering the event don't bother with radios. They don't get much utility, seeing as they can't send signals out, and very limited ability to only send signals to members already "deeper" in than themselves. In principle though, they can receive messages from a command site that was broadcasting from outside the event horizon. Provided they were not standing on the opposite side of the epi-centre to the broadcaster.

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In the real world of natural disasters, communications are critical to coordinating an emergency response. Responses over large areas and multiple crews usually use a combination of short-wave radio (which can be blocked by mountains and valleys) and cell networks (which require a bunch of potentially fragile infrastructure).

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That was just to give you an idea of the sort of thing I'd like to consider. I want to work on a setting where a team are trying to respond to some situation, but are somehow limited to one-way communication only.

In terms of real world scenarios I can think of at least two.

The first is a air-to-ground operation where the ground team have no radios, and are limited to low tech signalling, (ie rock formations, large logs, smoke). In this setting the air team could be tracking the location and intended movements of the ground team, but have no good way of signalling their own intentions (although they may hover in place / circle a location of interest).

The second is more historical. I'm thinking of the sort of voyages from the age of discovery, from the 13th century, until I guess around invention of the telegram. Any long distance mission really had a general set of orders, from a monarch, or Pope, but had no way of communicating operationally relevant details in any useful time frame. If the voyage encountered pirates, or a new land mass, it was really at the discretion of the ships captain as to how to proceed; be it fight, flight, or lay claim.

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I guess time is the biggest obstacle to two way communications. The time it takes for a message to get to the recipient, for them to process it, and for a reply to return to the sender. In my historical case, the time limit on a message is the same as the time it takes to move a person from one location to another (pigeons only work over limited distances). In "Anisotropy" messaging with radio would be instantaneous, but for a runner trying to communicate with onsite command, they are trying to send a message to the past.

Physical obstacles are also part of the problem. The ground team, in my other example, cannot practically get to the air team to listen to any message, and then safely back down. Like wise a large object, or metal barrier, can block radio waves from getting from one site to another.

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Returning to the Anisotropic event. I would like to think seriously about how a real world team would go about responding to an event like this. In particular what communications strategies they might develop, knowing that the field-operatives won't be able to talk-back.

Part of my response would be to setup a series of 3-4 transmit stations around the event, at some distance to get a reasonable view into it. These stations would be relaying messages from a central-command, broadcasting general instructions to anyone inside the event (ie "Walk towards the darkness", "Move slowly and calmly", "Avoid climbing or descending").

As for the runners themselves, I would imagine that part of their kit would include flouro-paint-pens and glow sticks. They could leave a trail of breadcrumbs to anyone who enters after them to show the path they had taken. This is more for the benefit of other runners, though. Anyone seeing the trail has no way of knowing if it leads to saftey or a literal dead end. However, a second runner can see the marks and may decide to diverge, to increase coverage of the rescue crew.

This feels to me about the best I can come up with.

Are there other strategies, or solutions that would help in this situation?

Answer 1

I have big troubles suspending my disbelief enough to accept a thing such as the described Anisotropy, one in which humans may still be able to live.

So follow me in a journey to the center of this Anisotropy

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Terminology:

• "in the future direction" - towards the center of the Anisotropy
• "in the past direction" - opposite to the "future direction", away from the center of the Anisotropy

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Start with the idea of a person that needs to be rescued. Most trivial case, the person is trapped in a concavity that doesn't allow her to advance towards the center. A rescuer can't see her until he is trapped in the same place.

Now, suppose the rescuer takes the absolutely blind risk of advancing in a concavity, just in case someone needs rescued there. So, he reaches the deadend too - what can he do?

Demolition charges? Yes, the rescuer may be able to throw one in the "towards center" direction and he will be safe from the shrapnel fragments (which cannot travel in the past). But doing so will kill whoever happens to be near or in "the near future" of the point the demolition charge explodes.

He can't even properly swing an axe - the back swing will "hit the past" - so that there's no "back half of the swing"; then the axe cannot be retracted after it hit something in "the future" direction, better hope one (half of a) blow is enough to clear the way.

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Now that I think of it, anything with a functioning heart and lungs will be drawn towards the center.

The walls of the heart going "into the future" during the diastole can't contract back "into the past" during the systole. The only way for the heart to contract back is to drag the side in past towards the future direction. 2-3 heartbeats and the one living creature will need to... ummm, how to put it... follows one's heart into the future or else stop it from beating?
Pretty much the same with the lungs.

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But, hang on, there's the Brownian motion too. Air molecules can't go into the direction of the past, right? Because if they do, one could communicate outside through sound and that's verboten.

Now, if my memory serves, the median speed of air molecules in their Brownian motion at normal temperature is between 300 m/s and 400 m/s. And the molecules can't go in the "past" direction.
Which means a wind of at least 200 m/s (averaging over half of the hemispheric solid angle oriented towards "the future"). So something like a wind of at least 720km/h, right?

But wait, that's not all. Recall now that the atoms/molecules of solid objects experience Brownian motion too. They themselves will be pushed "in the future" (or else sound communication will be possible by dragging a long steel cable inside and hitting it with a Morse hammer); granted, they'll progress towards the center at a lower speed than the air, but as inevitable as the "no time travel in the past".

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Heh, one on top of the other, not only the Anisotropy is hostile to anything alive, but imagine what happens in the center of the Anisotropy with all that mass that is irresistible pulled towards a single point.

To my mind, a blackhole happens. Now, I don't know what to hope for

1. Should I wish the Anisotropy is never lifted until the blackhole mass gets past the "very energetic Hawking radiation" stage? May take a significant mass, something like the entire Everest range, and then it's only a few centuries until the BH goes boom

2. Should I wish the Anisotropy is never lifted? Well, that's a "Good-bye Earth", all one can hope the rate of Anisotropy substance accumulation is lower than the accretion speed of the BH at its center (and thanks God the BH is "in the future" and cannot affect the-past me directly)

3. should I wish for the Anisotropy is lifted ASAP and everything around be done and dusted under and explosion of Hawking radiation?

Answer 2

The larger limiting factor that you seem to have mentioned then ignored is that apart from pre-event records there is no data about what lies beyond the event horizon. The best course of action available to a would-be rescue force in this scenario is to signal those within the event in every way possible to move inward then deploy S&R teams to comb inward along carefully planned routes based on the pre-event layout of the area within the event horizon to cover all possible routes to salvation. They've no way to know how successful those teams are, or their ultimate fate so they're going to have to send several waves along different full coverage routes to maximise their chances of success.

BUT

Realistically unless those outside know there is a way to survive past the barrier, and they have no data to indicate that there is, they're likely to assume everyone within is dead and unlikely to "throw good money after bad". Abandonment of those within by anyone not directly emotionally invested in their safety seems likely. Those who go in will have loved ones behind the barrier and going in after them will be seen as an elaborate form of suicide.