Hello world,

Just a noob question, I'm not much into physics, but always marvel at the wonders of it
If you cut or break something (for example a straw) is it possible, theoretically, to attach/repair (rearrange/connect the molecules again as it was before) the two halves together without a trace where it was cut? Maybe something similar happens when you make a cut in your finger, it heals without a scar.
Hope it made some sense what I tried to explain here.

Regards,

C.D.

Charles Dickens,

most repairs of this nature would have to involve heating the molecules up to a uniform state and then cooling them to return to the original configuration. An example is welding. However in practical terms, there is always a scar which as any engineer will tell you is where something will usually tear again, this is due to imperfections in the process, skill of the welder, inclusion of impurities and differential cooling. So I believe that even though the signs of the join may be hidden, the weakness must remain to some extent. Interestingly one of the first symptoms of scurvy (ancient maritimers curse) is that old scars become visible again and begin to bleed. The way the skin works is that it has two components, elastin and collogen. Elastin, is the elastic component of skin that gives it its stretch. Collogen is more rigid and provides the framework within which the elastin can stretch, collogens strength and rigidity will prevent the weaker elastin from overstretching. A scar I believe consists mainly of collogen which gradually fades away but I think that the relic of the scar in that area always remains.

Well, theoretically yes it's possible, because it not impossible. But the probability of such thing to occur is incredibly small. So small that it wouldn't occur not even once in the lifetime of our current Universe.
It would require a drastic decrease of entropy of the object.
To summarize, there is no fundamental law that forbid it to happen, but it will likely never happen.
I suggest you to read Poincaré recurrence theorem - Wikipedia, the free encyclopedia.

__________________
Isaac
If the problem is too hard just let the Universe solve it.

this is really physics speaking about its own limitations.

I agree. Nobody will ever cure his finger with a "special method" that don't keep any scar.
The same apply for objects as YellowPeril said.
I remember physicsquest saying he could access to Maccone's paper ... (Oh I just found it : http://arxiv.org/pdf/0802.0438v3) that might be of interest.
Something that repairs perfectly would not leave any trace of scar and according to Maccone, it seems that physics cannot study the process where entropy decreases, which would be the case here.
I'm not an expert on the matter though.
But what about the fluctuation theorem? (see Fluctuation theorem - Wikipedia, the free encyclopedia).
I'm confused.
Also in Physics, if you observe a strange phenomenon in your lab and you can't reproduce it, it will never matter to the scientific community. In the very, very, very improbable case of a perfect reparation, you can be sure that you'll never be able to reproduce it nor see it happens by itself. There's no technology that will ever be able to perfectly repair a system containing more than 10²³ particles.
I've once talked to one of my professor that told me he has been able to "reverse time" but for a system of few particles if I remember well. I'm sure you can search through his papers if you're interested (He is somewhat famous, I think he did a post doc at MIT). Send me a PM and I tell you his name.
To summarize: I think any physicist will tell you it's impossible to perfectly repair a cut macroscopic object. I'm just an odd student that thinks there's no fundamental law that completely forbid it. But that's just me.

__________________
Isaac
If the problem is too hard just let the Universe solve it.

did he do the experiment with antiparticles? i read in hawkings book that antiparticles travel backward in time.
maybe i can google search about his experiment?

As far as I know he didn't.
About antiparticles... I've read about them that we don't even know if they have a positive mass or a negative one!

__________________
Isaac
If the problem is too hard just let the Universe solve it.