English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Einstein's relativity theory appears to be very accurate, but at timesequally puzzling. On the one hand, electromagnetic radiation must have zerorest mass in order to propagate at the speed of light, but on the other hand,since it definitely carries momentum and energy, it has non-zero inertial mass.Hence, by the principle of equivalence, it must have non-zero gravitationalmass, and so, light must be heavy. In this paper, no new results will bederived, but a possibly surprising perspective on the above paradox is given.

Light is Heavy