[diverjohn (OP)]

While pondering the existence and consequence of faster than light particles, I wondered if tachyons are real and useful then we can travel the galaxy in years rather than in millennia. Then, given the large number of planets capable of supporting life, another civilization would have harnessed the ability to travel interstellar distances easily. However, as Enrico Fermi pointed out in his famous lunch time paradox, we have seen zero proof of alien contact. So, either advanced extraterrestrials don't exist or exceeding light speed in space travel is impossible. Any thoughts on this?

[Halc]

While pondering the existence and consequence of faster than light particles, I wondered if tachyons are real and useful then we can travel the galaxy in years rather than in millennia.

How would the reality of tachyons help you (or another civilization) get anywhere fast if you're not made of them?

However, as Enrico Fermi pointed out in his famous lunch time paradox, we have seen zero proof of alien contact. So, either advanced extraterrestrials don't exist or exceeding light speed in space travel is impossible. Any thoughts on this?

You suggest the only solution for the Fermi paradox is the light speed limitation.  Here we are such an advanced civilization and the fastest speed we've been able to achieve is under 0.0001c.  OK, I think we got a ship to go faster than that, but only by dropping off a cliff, not actually having the ship do it under its own power.  The speed of light hasn't exactly been a barrier to us yet.
Contact with aliens doesn't necessarily entail travel.  If they were out there on every 1000th planet, we'd notice.

[Hayseed]

I would think that aliens don't exist. At least within 13 billion years. The reason being that we can detect EM spectra from that time....and nothing is there.  Spectra should long precede any contact.

[evan_au]

On my recent vacation, I read the ebook version of Stephen Webb's book "If the Universe is Teeming with Aliens...Where is Everybody?".

This book lists 75 possible solutions to the Fermi Paradox that have been suggested by various academics and science-fiction writers (some of them are both...).

The difficulty of interstellar travel is certainly one of the reasons cited (another is knowing what frequencies or technologies aliens may wish to use for interstellar communication).

Various people have analysed the difficulties, and suggest that if self-replicating robots could be created, they should be able to search every star system in the galaxy in a few million years.

Anyway, Webb describes the options better than I can...

[yor_on]

Well, as a first guess tachyons exist outside our envelope. We're limited to 'c'. Considering the immense distances between suns, as well as the idea of space as a infinity, it seems reasonable to assume that it is very seldom some place gets 'contacted' by another 'space faring civilization'. And as we are at the fringe of our galaxy as I understands it even less probable. But there might be other ways to 'travel' this universe than moving mass. I'm not thinking of tachyons though.

[Janus]

I would think that aliens don't exist. At least within 13 billion years. The reason being that we can detect EM spectra from that time....and nothing is there.  Spectra should long precede any contact.

The ability to just detect EM at long distances doesn't mean that we would be able to discern signals created by an extraterrestrial civilization from the general background noise. It has been estimated that our Civilization's EM output would not be distinguishable from the background at any distance greater than 100 ly.   Beyond that, someone at our technological level would have to be deliberately beaming signals at us for them to be noticeable. That doesn't mean that extraterrestrial  civilizations aren't rare, or possibly non-existent, just that the lack of detecting signals from them is not proof of this.
Besides that, even if we were capable of detecting civilizations at much greater distances, the further away, the further back in time we are looking,  Looking at a star 5,000 ly away, we are looking at it as it was 5,000 yrs ago.  If it had a civilization equivalent to ours right now, we would be seeing it as it was 5000 yrs before it reached that level.  Conversely, if they were looking at us, they would see the world of 2981 BC. So even if the two civilizations were capable of detecting the present output of the other. Right now, they would not detect anything.  Expand that to billions of light years, and entire star systems could have formed and evolved life while the EMR crossed the distance.

[Bill S]

Looking at a star 5,000 ly away, we are looking at it as it was 5,000 yrs ago.  If it had a civilization equivalent to ours right now, we would be seeing it as it was 5000 yrs before it reached that level.  Conversely, if they were looking at us, they would see the world of 2981 BC

A corollary of that might be that if we received a signal sent 5000 yrs ago, the civilisation who sent it (if anything like ours) would probably have destroyed themselves long ago.

[diverjohn (OP)]

Good answers from all. Tachyons, if they exist, may be used to communicate at faster than light speeds. I agree that moving our spacecraft at speeds above C is fraught with currently insurmountable problems. Perhaps aliens are NOT using electromagnetic spectrum for their radio and television and that could be one explanation.

[evan_au]

The ability to just detect EM at long distances doesn't mean that we would be able to discern signals created by an extraterrestrial civilization from the general background noise.

In fact, there is a principle in information theory that if you want to encode information most efficiently for transmission, it will be indistinguishable from random noise - unless you know the encoding method.
- And since aliens haven't given us a manual on how to decode their signals, we probably won't be able to
- Unless they send a clearly non-natural, non-noise signal as a beacon to attract our attention
- The starshot Listen programme is looking for just such beacons.

For those old enough to remember dial-up modems connecting to the internet:
- Really old modems (300 bits per second (bps) = 0.0003 Mega bps (Mbps)) sounded like steady tones when not transmitting anything, and like warbling tones when transmitting
- Not so old modems (1200 bps = 0.0012 Mbps) sounded like random noise once they got going
- Newer, but still totally obsolete modems (56000 bps = 0.0056 Mbps) were also random noise
- The same noise characteristic also goes for newer broadband technologies like VDSL2, DOCSIS 3, satellite transmission, 5G mobile, etc, just over a wider frequency band.

See: https://en.wikipedia.org/wiki/Breakthrough_Listen

[Hayseed]

Any theory or any reasoning of alien life, has to be made with many assumptions.  The assumption of non-existence has one assumption.

Plus the lack of evidence, for any reason, gives that assumption preponderance.

So, until some evidence is detected, the reasonable assumption is negative.

Also, if life came from nature or a natural process, basic life forms would be common everywhere.

Life is the only singularity ever detected.

[Hayseed]

I have read some think that 'c" is broken regularly. Not with EM, but thru charge fields under the right configurations and conditions.  Some even think it is common in current and lightning. And possibly an anti-matter connection with the lightening.

I guess it would depend on what one thinks a field is.

I think that a wave, is an inverted field.  A field that has been turned inside-out.

Then there is the apparent FLT with moon reflections.  But, being no info can be transferred, they say it doesn't count.

[yor_on]

You are correct in assuming that 'c' not only becomes a limit of propagation. It's also a limit of useful information. That's why entanglements that seems 'instantaneous' are presumed to be unable to carry information. But it's also a question of how we define a universe as I suspect. Nevertheless, we're limited to 'c' here.