# If you're moving at a speed exponentially faster than the speed of light, can you still see each other? [closed]

My story is set in the future, where organisms have long since evolved to speeds beyond the speed of light. The only problem is that I can't quite work out how can they can see each other since light is out of the question. I have already abandoned hearing as a sensible sense and I am thinking of abandoning sight altogether.

p.s.: They're not humans, so forget about human anatomy.

## closed as unclear what you're asking by Mołot, L.Dutch♦, Hohmannfan, Youstay Igo, AzuaronMar 22 '17 at 13:03

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• FTL is not real, so combining it with reality check tag seems strange. – Mołot Mar 21 '17 at 18:53
• Since FTL is impossible, by definition everything is impossible at FTL. – sphennings Mar 21 '17 at 19:00
• @khaloodxp reality-check would work IF you told us more about how your physics works when going FTL. Reality-check asks us to check your model, but we need the whole model. – SRM Mar 21 '17 at 19:08
• Can you clarify what you mean by "exponentially faster"? – HDE 226868 Mar 22 '17 at 0:04
• What @HDE226868 said; I don't think "exponentially" means what you think it means, or at least what you used it for. If you want a fancy term, "superluminal" can substitute for "faster than light", or you could use something like "several times the speed of light" if you want to emphasize the magnitude. – a CVn Mar 22 '17 at 9:49

Is this the Newtonian light world? Ether is back? If so, I expect that a critter moving faster than the speed of light would be analogous to a plane moving faster than the speed of sound. If the plane is coming right at you, you do not hear it coming. But when it is next to you then you definitely hear it when the sonic boom hits you. Just as a plane accumulates sound in front if it your critters would accumulate light that was pushed along in advance. Here is how it works with sound.

So when one of these passed by, it would be very bright when the "shock wave" hit you. From the rear you would be able to see something - not the tail end because light would not catch up with it to hit and bounce back. But scattered light coming from the side / below etc would bounce off tangentially.

Probably the polite thing to do would be to slow down if you wanted to interact.

• Is it the same? The sound energy the plane is accumulating is due to it being generated by it flying through the air and I suppose its engines (?), whereas presumably the creature moving faster than light isn't actually creating any light itself, so I don't think there would be a bright flash or "luminal boom"... – colmde Mar 22 '17 at 9:26
• @colmde isn't it because you are flying faster than the sound you are constantly emitting, so the sound at first goes to the direction your flying in (and every other) but as you are faster than that sound it actually follows you not the other way around and mixes with the new sound you are making backwards. – DonQuiKong Mar 22 '17 at 10:00
• colmde - you do not emit light but unless we are together in a darkened room I see you because of the light you reflect. Similar? I think DonQui has got it. I feel some license to MSU because we have given light a medium for purposes of this question. I am very much digging the term "luminal boom" and that needs to stay regardless. – Willk Mar 22 '17 at 15:43

Short answer, they can't, even gravity only moves at light speed.

They have to slow down to know where anything is.

correction they can see things they are moving directly toward as they literally run into the light, it would be black and white only however as frequency is all the same.

• They can run into the light, but can their brains record it? Everything breaks down at the FTL border. – SRM Mar 21 '17 at 19:06

I don't think the "reality-check" tag is appropriate here because of course there's nothing realistic about moving faster than light anyway.

So the answer must ignore all the relativistic stuff that happens as they approach the speed of light, and just regard light as an energy transfer with a limited speed (like sound)

First of all, they could not see anything behind them, because they're outrunning its light. So what happens if they look backwards? Complete darkness.

Secondly, there would be severe doppler-effect type issues for seeing anything in front of them, so depending on how fast they're going, visible light might well be increased to a frequency that is outside the visible spectrum, and infra-red is now in the visible spectrum.

But the key here is that all this is happening through evolution. Evolution is a gradual process, so as they evolve the ability to move at higher speeds, they must also evolve the vision sense to see light frequencies higher than we can, as well as process information at the higher speeds - otherwise the high speed ability would be useless, cause them to kill themselves by crashing into things and therefore they would be removed from the gene pool, and the faster than light evolution would have never taken hold.

That being the case, they are most likely evolving the ability to see each other while moving at FTL speed, even though the light itself would form nothing like their shape as we think of it, their brains would have evolved to reprocess the information into the correct shape so what they would "see" would a correct image. (Similar to how our brains process the two separate images from our two eyes into a single 3-D image)

Of course they will only ever be able to see within a limited field of vision in front of them. The light from outside that field simply isn't reaching them.

We don't know of any senses that could work faster then the speed of light. You could do telepathy, or something even more exotic. But yes sight is out of the question.

There is just no measurable information transfer that beats the speed of light. So you need something we can't measure. So telepathy fits that bill. Or even aura sensing. Anything unscientific/magic really.

• thanks, it seems like I'll have to create a whole new set of senses altogether – Khaloodxp Mar 21 '17 at 18:46
• More importantly, find a way to transfer the data faster then the speed of light. Magnetic fields, electric fields, vibrations etc are all still to slow. – Mormacil Mar 21 '17 at 18:48
• I already handled data transfer it's a pseudo-scientific system , and I already have aura sensing and telepathy (to a minor extent where you can choose which info in your mind to send to others and which to keep private) but I can't seem to think of other possible senses – Khaloodxp Mar 21 '17 at 18:51

Matter cannot reach the speed of light and certainty cannot exceed it. This isn't a guideline. It's a fundamental fact of the universe. It may be possible to get from A to B in less time than it should take to traverse that distance, but only by finding some cheat where you didn't actually travel the full distance: A jaunt outside the normal universe might serve, a protected pocket universe, a severe warping of space. (Imagine your ship is a marble rolling on a sheet, grab the marble from the underside of the sheet, yank the marble to the other side, poke a hole through both layers and the marble pops out in a new place without crossing the sheet, be sure to stitch up afterwards or your friends will fall out of space and end up on the floor of the gods) All of these scenarios would allow for sight. And since none of them exist yet, sight can behave any way you like.

Objects in mirror are closer than they appear.

Disclaimer: This post consists predominantly of statements that sound cool, but have only the thinnest relationship with reality. This will not work in real life.

Gravitational lensing is a phenomonon by which a huge mass bends light, thereby distorting the apparent location of an object. Astronomers in real life have used this effect as a space magnifying glass to see distant galaxies. If your aliens could create micro black holes, or maybe they actually ARE micro black holes, they could theoretically use this light bending trick as a side view mirror. By bending light towards themselves, and calculating the amount of distortion in the image, they could plausibly have some degree of vision. Note there would still be some lag time - They could see where an object WAS and then make an educated guess as where it IS, but I don't think you could pull off real-time sight with this trick. You would have to accelerate/bend the light to go faster than the speed of light, which would be tough. Although...this post is describing FTL aliens using portable dark matter as a sensor array. So if you want to make the effect real-time, I don't think that's much more of a stretch.

They also wouldn't be able to see directly behind themselves. Their blind spot cone would widen in relation to how much beyone lightspeed they were traveling. At least, that sounds right to me...I am not a scientist.

Bibliography:

I used the Gravity's Lens article from One Minute Astronomer as research for this post.

http://oneminuteastronomer.com/9237/gravitational-lens/

I also used a lifetime of listening to quasi-scientific Star Trek tech explanations to make it sound good.