wouldn't it just stretch space time out the opposite direction. Also matters with a positive mass is attracted to space time that has been warped in that direction tachyons stretch it in the other way so wouldn't it be repelled matters way of stretching it.

The underlying material with gravity is complicated. I don't understand it well at all (my understanding of GR isn't very good). But I can be sure that the gravitational issues with tachyons are not going to be easily noodlable without a lot more math. This is a waste of time.

And now to deal with Jack...

It means objects with mass cannot accelerate past (or, in layman terms, travel past) the speed of light. Make sense now?

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Ok, if that's what you meant then it is confused. This is only true for objects with positive real mass.

Expansion of space is a completely separate issue which has nothing at all to do with tachyons.

We're not arguing about that. Please be consistent with the discussion.

Well excuse me for replying to what you quoted from Wikipedia. You seem to be missing the point. That's about travel within space (roughly speaking, the details are more complicated).

You can't accelerate an object with mass faster than the speed of light, under SR. Period.

You can't accelerate an object with positive real rest mass faster than the speed of light under SR. That's not the same. Tachyons don't have a positive real rest mass.

It is a function of the rest mass and the current velocity. But strictly speaking, there are no restrictions on the rest mass of a tachyon within special relativity beyond that it needs to be a non-zero imaginary number. But like all particles you have E= (mc^2)/(1- v^2/c^2)^(1/2) where m is the rest mass and E is the total energy (you get Einstein's well known equation from setting v=0 in the above).

So, what is the value of this imaginary mass of a tachyon just so it doesn't violate SR?

Some number of the form ki for k a non-zero real number.

Please take a physics course.

Good, so you have nothing to add to your argument. Gotcha.

There's no need for a new argument. If you don't understand the relevant equations that's not my fault. If you don't have time to take a physics course then crack open a book on special relativity.

Ok. Last attempt to explain this. Trying another tact. Let's think what goes wrong when we try to accelerate an object to the speed of light. Quick change of notation. I'm going to use capital M as the rest mass and little m as the relativistic mass. SR says in part that for normal particles relative mass is increases as we increase velocity. In fact, it says a bit more, namely that for any particle we have m(1- v^2/c^2)^(1/2)= M or if you prefer m= M/(1- v^2/c^2)^(1/2). Now, if M and m are non-zero then we get a problem if v=c because in that case we would have 1-v^2/c^2=0 and so we would get M*0=0=m which would be bad. Now, if m=M=0 this isn't a problem. That's why particles with mass zero can go the speed of light (for other reasons they have to go the speed of light). We similarly get a problem if we let v exceed c because we get an imaginary number if we have v>c. But, that's ok if we allow M or m to be imaginary numbers. The equations are consistent. If you look at the other relevant equations of SR you'll find that they are also consistent but you get strange acting particles. In particular, these particles still have the same problem if you try to set v=c so you can't ever get these particles to the speed of light. There are some other weird issues here and I'm a number theorist not a physicist so I don't feel comfortable going into that much more detail without picking up a textbook but that's the basic idea.