ARM by Larry Niven

could show that no killer could possibly have left the scene of the crime without Janice Sinclair's help, and therefore ... But what about that glowing thing, that time machine built by the dead man? Could it have freed a killer from an effectively locked room? How could a judge know its power?
    Well, could it?
    Bera might know.
    The machine was running. I caught the faint violet glow as I stepped into the laboratory and a flickering next to it ... and then it was off, and Jackson Bera stood suddenly beside it, grinning, silent, waiting.
    I wasn't about to spoil his fun. I said, “Well? Is it an interstellar drive?”
    “Yes!”
    A warm glow spread through me. I said, “Okay.”
    “It's a low-inertia field,” said Bera. “Things inside lose most of their inertia ... not their mass, just the resistance to movement. Ratio of about five hundred to one. The interface is sharp as a razor. We think there are quantum levels involved.”
    “Uh huh. The field doesn't affect time directly?”
    “No, it ... I shouldn't say that. Who the hell knows what time really is? It affects chemical and nuclear reactions, energy release of all kinds ... but it doesn't affect the speed of light. You know, it's kind of kicky to be measuring the speed of light at 370 miles per second with honest instruments.”
    Dammit. I'd been half hoping it was an FTL drive. I said, “Did you ever find out what was causing that blue glow?”
    Bera laughed at me. “Watch.” He'd rigged a remote switch to turn the machine on. He used it, then struck a match and flipped it toward the blue glow. As it crossed an invisible barrier, the match flared violet-white for something less than an eye blink. I blinked. It had been like a flashbulb going off.
    I said, “Oh, sure . The machinery's warm.”
    “Right. The blue glow is just infrared radiation being boosted to violet when it enters normal time.”
    Bera shouldn't have had to tell me that. Embarrassed, I changed the subject. “But you said it was an interstellar drive.”
    “Yah. It's got drawbacks,” Bera said. “We can't just put a field around a whole starship. The crew would think they'd lowered the speed of light, but so what? A slowboat doesn't get that close to lightspeed anyway. They'd save a little trip time, but they'd have to live through it five hundred times as fast.”
    “How about if you just put the field around your fuel tanks?”
    Bera nodded. “That's what they'll probably do. Leave the motor and the life support system outside. You could carry a god-awful amount of fuel that way ... Well, it's not our department. Someone else'll be designing the starships,” he said a bit wistfully.
    “Have you thought of this thing in relation to robbing banks? Or espionage?”
    “If a gang could afford to build one of these jobs, they wouldn't need to rob banks.” He ruminated. “I hate making anything this big a UN secret. But I guess you're right. The average government could afford a whole stable of the things.”
    “Thus combining James Bond and the Flash.”
    He rapped on the plastic frame. “Want to try it?”
    “Sure,” I said.
    Heart to brain: THUD! What're you doing? You'll get us all killed! I knew we should never have put you in charge of things ... I stepped up to the generator, waited for Bera to scamper beyond range, then pulled the switch.
    Everything turned deep red. Bera became a statue.
    Well, here I was. The second hand on the wall clock had stopped moving. I took two steps forward and rapped with my knuckles. Rapped, hell: it was like rapping on contact cement. The invisible wall was tacky.
    I tried leaning on it for a minute or so. That worked fine until I tried to pull away, and then I knew I'd done something stupid. I was embedded in the interface. It took me another minute to pull loose, and then I went sprawling backward; I'd picked up too much inward velocity, and it all came into the field with me.
    At that, I'd been lucky. If I'd leaned there a little longer,