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Is it true that human in outer space can't differ right side and left side, with no other objects for reference?

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*around human no another solid –  Aspirin Jan 5 '12 at 23:19
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One way or another, this questions needs some serious work. If you would indicated that I have or have not gone in the right direction I'm sure someone would be willing to help. –  dmckee Jan 5 '12 at 23:52
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Related: physics.stackexchange.com/q/18729/2451 –  Qmechanic Jan 6 '12 at 7:41
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4 Answers 4

Presumably you are asking about the communication ambiguity in physics: can we unambiguously specify what we mean by "a right handed coordinate system" to a correspondent far away without a pre-arrnage communications channel (i.e. using SETI)?

For a long time the answer seemed to be "no", but the discovery of parity violation in 1957 changed the answer to "yes, as long as we're sure they are made of matter and not anti-matter".

The discovery of CP violation in 1964 changed the answer again to allow us to unambiguously specify both the distinction between right and left and the distinction between matter and anti-matter at the same time (though the specification is pretty complicated...).

So, long story short: The concept of "right-handedness" is unambiguous and can be communicated to any sufficiently technological correspondent.

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This is interesting information, but I think the OP has heard that one cannot define a unique "upwards" direction in space, and has extended this confusion to the left/right distinction as well. –  Colin K Jan 6 '12 at 2:46
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No, it's not true.

Suppose I'm floating in outer space (presumably in a space suit or something else to keep me alive). I'm still me, and I still know that, for example, my left hand is the one on the left, and my right hand is the one I can write with.

Even on Earth, we don't need environmental clues to distinguish left from right; it's more a matter of body awareness.

I'm curious: why would you think a human in outer space couldn't distinguish left from right?

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Left and Right can be used in different contexts. In most cases they work equally well in space but not quite always. Often when people talk about left or right they mean something relative to a person, e.g my left hand or my right eye or the book to my right. This works equally well in space because it is defined relative to the position of a person, not relative to gravity. Another use of left and right is to define a left hand screw or a right hand screw, again the distinction works equally well in space because it does not depend on the direction of gravity.

Finally we talk about something turning left or right, such as a car on a road or someone walking. In space this will only make sense if there is a convention for up or down. This might be determined by the object itself if it has a natural axis for up and down. However there could be cases where there is no reference to up and down, for example if a sphere shaped object changes direction without anything else to reference it to, you could not say that it turned to the left or right. On the ground you could say whether it turned to the left or right, unless it turned in a vertical plane. This is the only sense in which you can say that the distinction between left and right disappears in space, and it is rather contrived. Most uses of left and right that you would encounter in practice work equally well in space.

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As an ideal physical observer, you can only distinguish left and right by parity violation as said above. Or bring an asymmetric device marked left and right from Earth into space.

However, biologically you can distinguish left and right at any place, because your own brain and hands are asymmetric, so you have an inner sense of left and right. This cannot, however, be communicated to an alien.

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