No, but we predict it to be essentially impossible to observe a graviton. 
<a href="http:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;gr-qc&#x2F;0601043" rel="nofollow">http:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;gr-qc&#x2F;0601043</a>