transformers - How do Soundwave, Megatron, etc. change size and mass?

The original G1 Soundwave changed from a cassette deck (don't know what it is? Ask your parents!) to a robot that was the same size as robots that changed into cars. Similarly, Megatron changed into a gun that could be held by humans.

And other robots, all of similar sizes, changed into objects of different sizes: cassettes, cars, trucks and huge jets. (One Autobot triple changer, Broadside, changed from an aircraft to an aircraft carrier!)

Was this impossible feat ever explained? Or was it hand-wavey magic, like the Hulk?

Answer

Although there wasn't even an acknowledgement of changes in size in the animated shows (i.e. that's just how things were), there have been a few explanations within comics. The ones listed and described by the Teletraan I Transformers Wiki are as follows:

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  Parts compression (from Dreamwave comics): The notion that the Transformers in question, such as Astrotrain and Broadside, had many dense layers of armor in robot mode, which then slid out, expanding to create a much larger, but less-strongly-armored vehicle mode. Fans have referred to this as the "origami Transformers" explanation, and it appeared in the More Than Meets The Eye encyclopedia.

  
  


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  Mass conversion (from Dreamwave comics): This method put it that Transformers like Soundwave were intrinsically endowed with the ability to transform not simply their bodies, but their entire molecular structure. This ability, not under their conscious control, only activates when they transform, shifting their atoms according to a pre-determined schematic.

  
  


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  Megatron employs a mass-displacement sequence in IDW's Escalation, physically discarding a portion of his bodily mass to allow himself to shrink to a human-scaled pistol of appropriate weight and density. What with E equalling mc², the loss of this amount of mass (shunted to an undisclosed location in space and time) results in a volatile energy discharge, requiring bystanders to step away lest they be injured by the forces released - not that Megatron would care.

  
  

  Due to the energy shortage (and seeming near-total depletion of Transformers' primary fuel source, Energon) caused by their war, mass displacement hasn't been commonplace for a very long time. Since it requires a huge amount of energy, the technology had practically vanished until the discovery of Ore-13 on Earth.

  
  

One popular fanon explanation is subspace. The idea that Transformers can store equipment or portions of their body in an extradimensional space has been used to explain, among other things, Optimus Prime's magic trailer.