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We will not attend US conferences until our colleagues can.

Scientific thought is the common heritage of mankind
Abdus Salam, Nobel Prize in Physics 1979

Science is a global endeavour, which thrives on openness, fairness and collaboration. It is stifled and undermined by division and discrimination.

The United States has greatly benefited from free and open international collaboration, and has been one of its strongest promoters. Many of us work together with scientists in the US and have enjoyed the hospitality of its institutions or benefited from its facilities and grants. Many of us have studied, taught or worked in the US and formed close and lasting collaborations and friendships.

The US government has now issued an indiscriminate ban against people from seven countries entering the United States, based solely on their citizenship. This includes people with dual citizenship. Even though most of us are not personally affected, this undermines the foundations of our work, and our identity as scientists. While previous travel restrictions have already hurt scientific collaboration, the ban takes this to a new level.

In solidarity with our colleagues, we pledge not to take part in scientific conferences in the United States that cannot be attended by all, regardless of their nationality or religion. We urge the President of the United States to lift the ban on our colleagues and remove this barrier to science and international collaboration.

We welcome the statements against the travel ban issued by professional organisations such as the International Astronomical Union, and we urge others to speak out. We also welcome the support by many of our American colleagues. As international scientists, we refuse to be divided. We cannot, in good conscience, continue to enjoy privileges from which our colleagues, students and teachers are arbitrarily excluded.